doc/configuration.txt

                         ----------------------
                                 HAProxy
                          Configuration Manual
                         ----------------------
                            version 1.3.17
                             willy tarreau
                              2009/03/29


This document covers the configuration language as implemented in the version
specified above. It does not provide any hint, example or advice. For such
documentation, please refer to the Reference Manual or the Architecture Manual.

Note to documentation contributors : this document is formated with 80 columns
per line, with even number of spaces for indentation and without tabs. Please
follow these rules strictly so that it remains easily printable everywhere. If
a line needs to be printed verbatim and does not fit, please end each line with
a backslash ('\') and continue on next line.

HAProxy's configuration process involves 3 major sources of parameters :

  - the arguments from the command-line, which always take precedence
  - the "global" section, which sets process-wide parameters
  - the proxies sections which can take form of "defaults", "listen",
    "frontend" and "backend".

The configuration file syntax consists in lines beginning with a keyword
referenced in this manual, optionally followed by one or several parameters
delimited by spaces. If spaces have to be entered in strings, then they must be
preceeded by a backslash ('\') to be escaped. Backslashes also have to be
escaped by doubling them.

Some parameters involve values representating time, such as timeouts. These
values are generally expressed in milliseconds (unless explicitly stated
otherwise) but may be expressed in any other unit by suffixing the unit to the
numeric value. It is important to consider this because it will not be repeated
for every keyword. Supported units are :

  - us : microseconds. 1 microsecond = 1/1000000 second
  - ms : milliseconds. 1 millisecond = 1/1000 second. This is the default.
  - s  : seconds. 1s = 1000ms
  - m  : minutes. 1m = 60s = 60000ms
  - h  : hours.   1h = 60m = 3600s = 3600000ms
  - d  : days.    1d = 24h = 1440m = 86400s = 86400000ms


1. Global parameters
--------------------

Parameters in the "global" section are process-wide and often OS-specific. They
are generally set once for all and do not need being changed once correct. Some
of them have command-line equivalents.

The following keywords are supported in the "global" section :

 * Process management and security
   - chroot
   - daemon
   - gid
   - group
   - log
   - nbproc
   - pidfile
   - uid
   - ulimit-n
   - user
   - stats
  
 * Performance tuning
   - maxconn
   - maxpipes
   - noepoll
   - nokqueue
   - nopoll
   - nosepoll
   - nosplice
   - spread-checks
   - tune.maxaccept
   - tune.maxpollevents
  
 * Debugging
   - debug
   - quiet


1.1) Process management and security
------------------------------------

chroot <jail dir>
  Changes current directory to <jail dir> and performs a chroot() there before
  dropping privileges. This increases the security level in case an unknown
  vulnerability would be exploited, since it would make it very hard for the
  attacker to exploit the system. This only works when the process is started
  with superuser privileges. It is important to ensure that <jail_dir> is both
  empty and unwritable to anyone.
  
daemon
  Makes the process fork into background. This is the recommended mode of
  operation. It is equivalent to the command line "-D" argument. It can be
  disabled by the command line "-db" argument.

gid <number>
  Changes the process' group ID to <number>. It is recommended that the group
  ID is dedicated to HAProxy or to a small set of similar daemons. HAProxy must
  be started with a user belonging to this group, or with superuser privileges.
  See also "group" and "uid".
  
group <group name>
  Similar to "gid" but uses the GID of group name <group name> from /etc/group.
  See also "gid" and "user".
  
log <address> <facility> [max level]
  Adds a global syslog server. Up to two global servers can be defined. They
  will receive logs for startups and exits, as well as all logs from proxies
  configured with "log global".

  <address> can be one of:

        - An IPv4 address optionally followed by a colon and a UDP port. If
          no port is specified, 514 is used by default (the standard syslog
          port).

        - A filesystem path to a UNIX domain socket, keeping in mind
          considerations for chroot (be sure the path is accessible inside
          the chroot) and uid/gid (be sure the path is appropriately
          writeable).

  <facility> must be one of the 24 standard syslog facilities :

          kern   user   mail   daemon auth   syslog lpr    news
          uucp   cron   auth2  ftp    ntp    audit  alert  cron2
          local0 local1 local2 local3 local4 local5 local6 local7

  An optional level can be specified to filter outgoing messages. By default,
  all messages are sent. If a level is specified, only messages with a severity
  at least as important as this level will be sent. 8 levels are known :

	  emerg  alert  crit   err    warning notice info  debug

nbproc <number>
  Creates <number> processes when going daemon. This requires the "daemon"
  mode. By default, only one process is created, which is the recommended mode
  of operation. For systems limited to small sets of file descriptors per
  process, it may be needed to fork multiple daemons. USING MULTIPLE PROCESSES
  IS HARDER TO DEBUG AND IS REALLY DISCOURAGED. See also "daemon".

pidfile <pidfile>
  Writes pids of all daemons into file <pidfile>. This option is equivalent to
  the "-p" command line argument. The file must be accessible to the user
  starting the process. See also "daemon".

stats socket <path> [{uid | user} <uid>] [{gid | group} <gid>] [mode <mode>]
  Creates a UNIX socket in stream mode at location <path>. Any previously
  existing socket will be backed up then replaced. Connections to this socket
  will get a CSV-formated output of the process statistics in response to the
  "show stat" command followed by a line feed, more general process information
  in response to the "show info" command followed by a line feed, and a
  complete list of all existing sessions in response to the "show sess" command
  followed by a line feed.

  On platforms which support it, it is possible to restrict access to this
  socket by specifying numerical IDs after "uid" and "gid", or valid user and
  group names after the "user" and "group" keywords. It is also possible to
  restrict permissions on the socket by passing an octal value after the "mode"
  keyword (same syntax as chmod). Depending on the platform, the permissions on
  the socket will be inherited from the directory which hosts it, or from the
  user the process is started with.

stats timeout <timeout, in milliseconds>
  The default timeout on the stats socket is set to 10 seconds. It is possible
  to change this value with "stats timeout". The value must be passed in
  milliseconds, or be suffixed by a time unit among { us, ms, s, m, h, d }.

stats maxconn <connections>
  By default, the stats socket is limited to 10 concurrent connections. It is
  possible to change this value with "stats maxconn".

uid <number>
  Changes the process' user ID to <number>. It is recommended that the user ID
  is dedicated to HAProxy or to a small set of similar daemons. HAProxy must
  be started with superuser privileges in order to be able to switch to another
  one. See also "gid" and "user".

ulimit-n <number>
  Sets the maximum number of per-process file-descriptors to <number>. By
  default, it is automatically computed, so it is recommended not to use this
  option.

user <user name>
  Similar to "uid" but uses the UID of user name <user name> from /etc/passwd.
  See also "uid" and "group".


1.2) Performance tuning
-----------------------

maxconn <number>
  Sets the maximum per-process number of concurrent connections to <number>. It
  is equivalent to the command-line argument "-n". Proxies will stop accepting
  connections when this limit is reached. The "ulimit-n" parameter is
  automatically adjusted according to this value. See also "ulimit-n".

maxpipes <number>
  Sets the maximum per-process number of pipes to <number>. Currently, pipes
  are only used by kernel-based tcp splicing. Since a pipe contains two file
  descriptors, the "ulimit-n" value will be increased accordingly. The default
  value is maxconn/4, which seems to be more than enough for most heavy usages.
  The splice code dynamically allocates and releases pipes, and can fall back
  to standard copy, so setting this value too low may only impact performance.

noepoll
  Disables the use of the "epoll" event polling system on Linux. It is
  equivalent to the command-line argument "-de". The next polling system
  used will generally be "poll". See also "nosepoll", and "nopoll".

nokqueue
  Disables the use of the "kqueue" event polling system on BSD. It is
  equivalent to the command-line argument "-dk". The next polling system
  used will generally be "poll". See also "nopoll".

nopoll
  Disables the use of the "poll" event polling system. It is equivalent to the
  command-line argument "-dp". The next polling system used will be "select".
  It should never be needed to disable "poll" since it's available on all
  platforms supported by HAProxy. See also "nosepoll", and "nopoll" and
  "nokqueue".

nosepoll
  Disables the use of the "speculative epoll" event polling system on Linux. It
  is equivalent to the command-line argument "-ds". The next polling system
  used will generally be "epoll". See also "nosepoll", and "nopoll".

nosplice
  Disables the use of kernel tcp splicing between sockets on Linux. It is
  equivalent to the command line argument "-dS".  Data will then be copied
  using conventional and more portable recv/send calls. Kernel tcp splicing is
  limited to some very recent instances of kernel 2.6. Most verstions between
  2.6.25 and 2.6.28 are buggy and will forward corrupted data, so they must not
  be used. This option makes it easier to globally disable kernel splicing in
  case of doubt. See also "option splice-auto", "option splice-request" and
  "option splice-response".

spread-checks <0..50, in percent>
  Sometimes it is desirable to avoid sending health checks to servers at exact
  intervals, for instance when many logical servers are located on the same
  physical server. With the help of this parameter, it becomes possible to add
  some randomness in the check interval between 0 and +/- 50%. A value between
  2 and 5 seems to show good results. The default value remains at 0.

tune.maxaccept <number>
  Sets the maximum number of consecutive accepts that a process may perform on
  a single wake up. High values give higher priority to high connection rates,
  while lower values give higher priority to already established connections.
  This value is limited to 100 by default in single process mode. However, in
  multi-process mode (nbproc > 1), it defaults to 8 so that when one process
  wakes up, it does not take all incoming connections for itself and leaves a
  part of them to other processes. Setting this value to -1 completely disables
  the limitation. It should normally not be needed to tweak this value.

tune.maxpollevents <number>
  Sets the maximum amount of events that can be processed at once in a call to
  the polling system. The default value is adapted to the operating system. It
  has been noticed that reducing it below 200 tends to slightly decrease
  latency at the expense of network bandwidth, and increasing it above 200
  tends to trade latency for slightly increased bandwidth.


1.3) Debugging
---------------

debug
  Enables debug mode which dumps to stdout all exchanges, and disables forking
  into background. It is the equivalent of the command-line argument "-d". It
  should never be used in a production configuration since it may prevent full
  system startup.

quiet
  Do not display any message during startup. It is equivalent to the command-
  line argument "-q".


2) Proxies
----------

Proxy configuration can be located in a set of sections :
 - defaults <name>
 - frontend <name>
 - backend  <name>
 - listen   <name>

A "defaults" section sets default parameters for all other sections following
its declaration. Those default parameters are reset by the next "defaults"
section. See below for the list of parameters which can be set in a "defaults"
section. The name is optional but its use is encouraged for better readability.

A "frontend" section describes a set of listening sockets accepting client
connections.

A "backend" section describes a set of servers to which the proxy will connect
to forward incoming connections.

A "listen" section defines a complete proxy with its frontend and backend
parts combined in one section. It is generally useful for TCP-only traffic.

All proxy names must be formed from upper and lower case letters, digits,
'-' (dash), '_' (underscore) , '.' (dot) and ':' (colon). ACL names are
case-sensitive, which means that "www" and "WWW" are two different proxies.

Historically, all proxy names could overlap, it just caused troubles in the
logs. Since the introduction of content switching, it is mandatory that two
proxies with overlapping capabilities (frontend/backend) have different names.
However, it is still permitted that a frontend and a backend share the same
name, as this configuration seems to be commonly encountered.

Right now, two major proxy modes are supported : "tcp", also known as layer 4,
and "http", also known as layer 7. In layer 4 mode, HAProxy simply forwards
bidirectionnal traffic between two sides. In layer 7 mode, HAProxy analyzes the
protocol, and can interact with it by allowing, blocking, switching, adding,
modifying, or removing arbitrary contents in requests or responses, based on
arbitrary criteria.


2.1) Quick reminder about HTTP
------------------------------

When a proxy is running in HTTP mode, both the request and the response are
fully analyzed and indexed, thus it becomes possible to build matching criteria
on almost anything found in the contents.

However, it is important to understand how HTTP requests and responses are
formed, and how HAProxy decomposes them. It will then become easier to write
correct rules and to debug existing configurations.


2.1.1) The HTTP transaction model
---------------------------------

The HTTP protocol is transaction-driven. This means that each request will lead
to one and only one response. Traditionnally, a TCP connection is established
from the client to the server, a request is sent by the client on the
connection, the server responds and the connection is closed. A new request
will involve a new connection :

  [CON1] [REQ1] ... [RESP1] [CLO1] [CON2] [REQ2] ... [RESP2] [CLO2] ...

In this mode, called the "HTTP close" mode, there are as many connection
establishments as there are HTTP transactions. Since the connection is closed
by the server after the response, the client does not need to know the content
length.

Due to the transactional nature of the protocol, it was possible to improve it
to avoid closing a connection between two subsequent transactions. In this mode
however, it is mandatory that the server indicates the content length for each
response so that the client does not wait indefinitely. For this, a special
header is used: "Content-length". This mode is called the "keep-alive" mode :

  [CON] [REQ1] ... [RESP1] [REQ2] ... [RESP2] [CLO] ...

Its advantages are a reduced latency between transactions, and less processing
power required on the server side. It is generally better than the close mode,
but not always because the clients often limit their concurrent connections to
a smaller value. HAProxy currently does not support the HTTP keep-alive mode,
but knows how to transform it to the close mode.

A last improvement in the communications is the pipelining mode. It still uses
keep-alive, but the client does not wait for the first response to send the
second request. This is useful for fetching large number of images composing a
page :

  [CON] [REQ1] [REQ2] ... [RESP1] [RESP2] [CLO] ...

This can obviously have a tremendous benefit on performance because the network
latency is eliminated between subsequent requests. Many HTTP agents do not
correctly support pipelining since there is no way to associate a response with
the corresponding request in HTTP. For this reason, it is mandatory for the
server to reply in the exact same order as the requests were received.

Right now, HAProxy only supports the first mode (HTTP close) if it needs to
process the request. This means that for each request, there will be one TCP
connection. If keep-alive or pipelining are required, HAProxy will still
support them, but will only see the first request and the first response of
each transaction. While this is generally problematic with regards to logs,
content switching or filtering, it most often causes no problem for persistence
with cookie insertion.


2.1.2) HTTP request
-------------------

First, let's consider this HTTP request :

  Line     Contents
  number 
     1     GET /serv/login.php?lang=en&profile=2 HTTP/1.1
     2     Host: www.mydomain.com
     3     User-agent: my small browser
     4     Accept: image/jpeg, image/gif
     5     Accept: image/png


2.1.2.1) The Request line
-------------------------

Line 1 is the "request line". It is always composed of 3 fields :

  - a METHOD      : GET
  - a URI         : /serv/login.php?lang=en&profile=2
  - a version tag : HTTP/1.1

All of them are delimited by what the standard calls LWS (linear white spaces),
which are commonly spaces, but can also be tabs or line feeds/carriage returns
followed by spaces/tabs. The method itself cannot contain any colon (':') and
is limited to alphabetic letters. All those various combinations make it
desirable that HAProxy performs the splitting itself rather than leaving it to
the user to write a complex or inaccurate regular expression.

The URI itself can have several forms :

  - A "relative URI" :

      /serv/login.php?lang=en&profile=2

    It is a complete URL without the host part. This is generally what is
    received by servers, reverse proxies and transparent proxies.

  - An "absolute URI", also called a "URL" :

      http://192.168.0.12:8080/serv/login.php?lang=en&profile=2

    It is composed of a "scheme" (the protocol name followed by '://'), a host
    name or address, optionally a colon (':') followed by a port number, then
    a relative URI beginning at the first slash ('/') after the address part.
    This is generally what proxies receive, but a server supporting HTTP/1.1
    must accept this form too.

  - a star ('*') : this form is only accepted in association with the OPTIONS
    method and is not relayable. It is used to inquiry a next hop's
    capabilities.
        
  - an address:port combination : 192.168.0.12:80
    This is used with the CONNECT method, which is used to establish TCP
    tunnels through HTTP proxies, generally for HTTPS, but sometimes for
    other protocols too.

In a relative URI, two sub-parts are identified. The part before the question
mark is called the "path". It is typically the relative path to static objects
on the server. The part after the question mark is called the "query string".
It is mostly used with GET requests sent to dynamic scripts and is very
specific to the language, framework or application in use.


2.1.2.2) The request headers
----------------------------

The headers start at the second line. They are composed of a name at the
beginning of the line, immediately followed by a colon (':'). Traditionally,
an LWS is added after the colon but that's not required. Then come the values.
Multiple identical headers may be folded into one single line, delimiting the
values with commas, provided that their order is respected. This is commonly
encountered in the "Cookie:" field. A header may span over multiple lines if
the subsequent lines begin with an LWS. In the example in 2.1.2, lines 4 and 5
define a total of 3 values for the "Accept:" header.

Contrary to a common mis-conception, header names are not case-sensitive, and
their values are not either if they refer to other header names (such as the
"Connection:" header).

The end of the headers is indicated by the first empty line. People often say
that it's a double line feed, which is not exact, even if a double line feed
is one valid form of empty line.

Fortunately, HAProxy takes care of all these complex combinations when indexing
headers, checking values and counting them, so there is no reason to worry
about the way they could be written, but it is important not to accuse an
application of being buggy if it does unusual, valid things.

Important note:
   As suggested by RFC2616, HAProxy normalizes headers by replacing line breaks
   in the middle of headers by LWS in order to join multi-line headers. This
   is necessary for proper analysis and helps less capable HTTP parsers to work
   correctly and not to be fooled by such complex constructs.


2.1.3) HTTP response
--------------------

An HTTP response looks very much like an HTTP request. Both are called HTTP
messages. Let's consider this HTTP response :

  Line     Contents
  number 
     1     HTTP/1.1 200 OK
     2     Content-length: 350
     3     Content-Type: text/html


2.1.3.1) The Response line
--------------------------

Line 1 is the "response line". It is always composed of 3 fields :

  - a version tag : HTTP/1.1
  - a status code : 200
  - a reason      : OK

The status code is always 3-digit. The first digit indicates a general status :
 - 2xx = OK, content is following   (eg: 200, 206)
 - 3xx = OK, no content following   (eg: 302, 304)
 - 4xx = error caused by the client (eg: 401, 403, 404)
 - 5xx = error caused by the server (eg: 500, 502, 503)

Please refer to RFC2616 for the detailed meaning of all such codes. The
"reason" field is just a hint, but is not parsed by clients. Anything can be 
found there, but it's a common practice to respect the well-established
messages. It can be composed of one or multiple words, such as "OK", "Found",
or "Authentication Required".

Haproxy may emit the following status codes by itself :

  Code  When / reason
   200  access to stats page, and when replying to monitoring requests
   301  when performing a redirection, depending on the configured code
   302  when performing a redirection, depending on the configured code
   303  when performing a redirection, depending on the configured code
   400  for an invalid or too large request
   401  when an authentication is required to perform the action (when
        accessing the stats page)
   403  when a request is forbidden by a "block" ACL or "reqdeny" filter
   408  when the request timeout strikes before the request is complete
   500  when haproxy encounters an unrecoverable internal error, such as a
        memory allocation failure, which should never happen
   502  when the server returns an empty, invalid or incomplete response, or
        when an "rspdeny" filter blocks the response.
   503  when no server was available to handle the request, or in response to
        monitoring requests which match the "monitor fail" condition
   504  when the response timeout strikes before the server responds

The error 4xx and 5xx codes above may be customized (see "errorloc" in section
2.2).


2.1.3.2) The response headers
-----------------------------

Response headers work exactly like request headers, and as such, HAProxy uses
the same parsing function for both. Please refer to paragraph 2.1.2.2 for more
details.


2.2) Proxy keywords matrix
--------------------------

The following list of keywords is supported. Most of them may only be used in a
limited set of section types. Some of them are marked as "deprecated" because
they are inherited from an old syntax which may be confusing or functionally
limited, and there are new recommended keywords to replace them. Keywords
listed with [no] can be optionally inverted using the "no" prefix, ex. "no
option contstats". This makes sense when the option has been enabled by default
and must be disabled for a specific instance.


keyword                 defaults   frontend   listen    backend
----------------------+----------+----------+---------+---------
acl                         -          X         X         X   
appsession                  -          -         X         X   
backlog                     X          X         X         -
balance                     X          -         X         X   
bind                        -          X         X         -   
bind-process                X          X         X         X   
block                       -          X         X         X
capture cookie              -          X         X         -
capture request header      -          X         X         -
capture response header     -          X         X         -
clitimeout                  X          X         X         -  (deprecated)
contimeout                  X          -         X         X  (deprecated)
cookie                      X          -         X         X
default_backend             -          X         X         -
disabled                    X          X         X         X
dispatch                    -          -         X         X
enabled                     X          X         X         X
errorfile                   X          X         X         X
errorloc                    X          X         X         X
errorloc302                 X          X         X         X
errorloc303                 X          X         X         X
fullconn                    X          -         X         X
grace                       -          X         X         X
http-check disable-on-404   X          -         X         X
log                         X          X         X         X
maxconn                     X          X         X         -
mode                        X          X         X         X
monitor fail                -          X         X         -
monitor-net                 X          X         X         -
monitor-uri                 X          X         X         -
[no] option abortonclose    X          -         X         X
[no] option accept-invalid-
            http-request    X          X         X         -
[no] option accept-invalid-
            http-response   X          -         X         X
[no] option allbackups      X          -         X         X
[no] option checkcache      X          -         X         X
[no] option clitcpka        X          X         X         -
[no] option contstats       X          X         X         -
[no] option dontlognull     X          X         X         -
[no] option forceclose      X          -         X         X
option forwardfor           X          X         X         X
option originalto           X          X         X         X
[no] option http_proxy      X          X         X         X
option httpchk              X          -         X         X
[no] option httpclose       X          X         X         X
option httplog              X          X         X         X
[no] option logasap         X          X         X         -
[no] option nolinger        X          X         X         X
[no] option persist         X          -         X         X
[no] option redispatch      X          -         X         X
option smtpchk              X          -         X         X
[no] option splice-auto     X          X         X         X
[no] option splice-request  X          X         X         X
[no] option splice-response X          X         X         X
[no] option srvtcpka        X          -         X         X
option ssl-hello-chk        X          -         X         X
option tcpka                X          X         X         X
option tcplog               X          X         X         X
[no] option tcpsplice       X          X         X         X
[no] option transparent     X          -         X         X
rate-limit sessions         X          X         X         -
redirect                    -          X         X         X
redisp                      X          -         X         X  (deprecated)
redispatch                  X          -         X         X  (deprecated)
reqadd                      -          X         X         X
reqallow                    -          X         X         X
reqdel                      -          X         X         X
reqdeny                     -          X         X         X
reqiallow                   -          X         X         X
reqidel                     -          X         X         X
reqideny                    -          X         X         X
reqipass                    -          X         X         X
reqirep                     -          X         X         X
reqisetbe                   -          X         X         X
reqitarpit                  -          X         X         X
reqpass                     -          X         X         X
reqrep                      -          X         X         X
reqsetbe                    -          X         X         X
reqtarpit                   -          X         X         X
retries                     X          -         X         X
rspadd                      -          X         X         X
rspdel                      -          X         X         X
rspdeny                     -          X         X         X
rspidel                     -          X         X         X
rspideny                    -          X         X         X
rspirep                     -          X         X         X
rsprep                      -          X         X         X
server                      -          -         X         X
source                      X          -         X         X
srvtimeout                  X          -         X         X  (deprecated)
stats auth                  X          -         X         X
stats enable                X          -         X         X
stats realm                 X          -         X         X
stats refresh               X          -         X         X
stats scope                 X          -         X         X
stats uri                   X          -         X         X
stats hide-version          X          -         X         X
tcp-request content accept  -          X         X         -
tcp-request content reject  -          X         X         -
tcp-request inspect-delay   -          X         X         -
timeout check               X          -         X         X
timeout client              X          X         X         -
timeout clitimeout          X          X         X         -  (deprecated)
timeout connect             X          -         X         X
timeout contimeout          X          -         X         X  (deprecated)
timeout http-request        X          X         X         -
timeout queue               X          -         X         X
timeout server              X          -         X         X
timeout srvtimeout          X          -         X         X  (deprecated)
timeout tarpit              X          X         X         X
transparent                 X          -         X         X  (deprecated)
use_backend                 -          X         X         -
----------------------+----------+----------+---------+---------
keyword                 defaults   frontend   listen    backend


2.2.1) Alphabetically sorted keywords reference
-----------------------------------------------

This section provides a description of each keyword and its usage.


acl <aclname> <criterion> [flags] [operator] <value> ...
  Declare or complete an access list.
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    yes   |   yes  |   yes
  Example:
        acl invalid_src  src          0.0.0.0/7 224.0.0.0/3
        acl invalid_src  src_port     0:1023
        acl local_dst    hdr(host) -i localhost

  See section 2.3 about ACL usage.


appsession <cookie> len <length> timeout <holdtime>
  Define session stickiness on an existing application cookie.
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    no    |   yes  |   yes
  Arguments :
    <cookie>   this is the name of the cookie used by the application and which
               HAProxy will have to learn for each new session.

    <length>   this is the number of characters that will be memorized and
               checked in each cookie value.

    <holdtime> this is the time after which the cookie will be removed from
               memory if unused. If no unit is specified, this time is in
               milliseconds.

  When an application cookie is defined in a backend, HAProxy will check when
  the server sets such a cookie, and will store its value in a table, and
  associate it with the server's identifier. Up to <length> characters from
  the value will be retained. On each connection, haproxy will look for this
  cookie both in the "Cookie:" headers, and as a URL parameter in the query
  string. If a known value is found, the client will be directed to the server
  associated with this value. Otherwise, the load balancing algorithm is
  applied. Cookies are automatically removed from memory when they have been
  unused for a duration longer than <holdtime>.

  The definition of an application cookie is limited to one per backend.

  Example :
        appsession JSESSIONID len 52 timeout 3h

  See also : "cookie", "capture cookie" and "balance".


backlog <conns>
  Give hints to the system about the approximate listen backlog desired size
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   no
  Arguments :
    <conns>   is the number of pending connections. Depending on the operating
              system, it may represent the number of already acknowledged
	      connections, of non-acknowledged ones, or both.

  In order to protect against SYN flood attacks, one solution is to increase
  the system's SYN backlog size. Depending on the system, sometimes it is just
  tunable via a system parameter, sometimes it is not adjustable at all, and
  sometimes the system relies on hints given by the application at the time of
  the listen() syscall. By default, HAProxy passes the frontend's maxconn value
  to the listen() syscall. On systems which can make use of this value, it can
  sometimes be useful to be able to specify a different value, hence this
  backlog parameter.

  On Linux 2.4, the parameter is ignored by the system. On Linux 2.6, it is
  used as a hint and the system accepts up to the smallest greater power of
  two, and never more than some limits (usually 32768).

  See also : "maxconn" and the target operating system's tuning guide.


balance <algorithm> [ <arguments> ]
balance url_param <param> [check_post [<max_wait>]]
  Define the load balancing algorithm to be used in a backend.
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments :
    <algorithm> is the algorithm used to select a server when doing load
                balancing. This only applies when no persistence information
                is available, or when a connection is redispatched to another
                server. <algorithm> may be one of the following :

      roundrobin  Each server is used in turns, according to their weights.
                  This is the smoothest and fairest algorithm when the server's
                  processing time remains equally distributed. This algorithm
                  is dynamic, which means that server weights may be adjusted
                  on the fly for slow starts for instance.

      leastconn   The server with the lowest number of connections receives the
                  connection. Round-robin is performed within groups of servers
                  of the same load to ensure that all servers will be used. Use
                  of this algorithm is recommended where very long sessions are
                  expected, such as LDAP, SQL, TSE, etc... but is not very well
                  suited for protocols using short sessions such as HTTP. This
                  algorithm is dynamic, which means that server weights may be
                  adjusted on the fly for slow starts for instance.

      source      The source IP address is hashed and divided by the total
                  weight of the running servers to designate which server will
                  receive the request. This ensures that the same client IP
                  address will always reach the same server as long as no
                  server goes down or up. If the hash result changes due to the
                  number of running servers changing, many clients will be
                  directed to a different server. This algorithm is generally
                  used in TCP mode where no cookie may be inserted. It may also
                  be used on the Internet to provide a best-effort stickyness
                  to clients which refuse session cookies. This algorithm is
                  static, which means that changing a server's weight on the
                  fly will have no effect.

      uri         The left part of the URI (before the question mark) is hashed
                  and divided by the total weight of the running servers. The
                  result designates which server will receive the request. This
                  ensures that a same URI will always be directed to the same
                  server as long as no server goes up or down. This is used
                  with proxy caches and anti-virus proxies in order to maximize
                  the cache hit rate. Note that this algorithm may only be used
                  in an HTTP backend. This algorithm is static, which means
                  that changing a server's weight on the fly will have no
                  effect.

                  This algorithm support two optional parameters "len" and
                  "depth", both followed by a positive integer number. These
                  options may be helpful when it is needed to balance servers
                  based on the beginning of the URI only. The "len" parameter
                  indicates that the algorithm should only consider that many
                  characters at the beginning of the URI to compute the hash.
                  Note that having "len" set to 1 rarely makes sense since most
                  URIs start with a leading "/".

                  The "depth" parameter indicates the maximum directory depth
                  to be used to compute the hash. One level is counted for each
                  slash in the request. If both parameters are specified, the
                  evaluation stops when either is reached.

      url_param   The URL parameter specified in argument will be looked up in
                  the query string of each HTTP GET request.

                  If the modifier "check_post" is used, then an HTTP POST
		  request entity will be searched for the parameter argument,
		  when the question mark indicating a query string ('?') is not
		  present in the URL. Optionally, specify a number of octets to
		  wait for before attempting to search the message body. If the
		  entity can not be searched, then round robin is used for each
		  request. For instance, if your clients always send the LB
		  parameter in the first 128 bytes, then specify that. The
		  default is 48. The entity data will not be scanned until the
		  required number of octets have arrived at the gateway, this
		  is the minimum of: (default/max_wait, Content-Length or first
		  chunk length). If Content-Length is missing or zero, it does
		  not need to wait for more data than the client promised to
		  send. When Content-Length is present and larger than
		  <max_wait>, then waiting is limited to <max_wait> and it is
		  assumed that this will be enough data to search for the
		  presence of the parameter. In the unlikely event that
		  Transfer-Encoding: chunked is used, only the first chunk is
		  scanned. Parameter values separated by a chunk boundary, may
		  be randomly balanced if at all.

                  If the parameter is found followed by an equal sign ('=') and
                  a value, then the value is hashed and divided by the total
                  weight of the running servers. The result designates which
                  server will receive the request.

                  This is used to track user identifiers in requests and ensure
                  that a same user ID will always be sent to the same server as
                  long as no server goes up or down. If no value is found or if
                  the parameter is not found, then a round robin algorithm is
                  applied. Note that this algorithm may only be used in an HTTP
                  backend. This algorithm is static, which means that changing a
                  server's weight on the fly will have no effect.

    <arguments> is an optional list of arguments which may be needed by some
                algorithms. Right now, only "url_param" and "uri" support an
                optional argument.

                balance uri [len <len>] [depth <depth>]
                balance url_param <param> [check_post [<max_wait>]]

  The load balancing algorithm of a backend is set to roundrobin when no other
  algorithm, mode nor option have been set. The algorithm may only be set once
  for each backend.

  Examples :
        balance roundrobin
        balance url_param userid
        balance url_param session_id check_post 64

  Note: the following caveats and limitations on using the "check_post"
  extension with "url_param" must be considered :

    - all POST requests are eligable for consideration, because there is no way
      to determine if the parameters will be found in the body or entity which
      may contain binary data. Therefore another method may be required to
      restrict consideration of POST requests that have no URL parameters in
      the body. (see acl reqideny http_end)

    - using a <max_wait> value larger than the request buffer size does not
      make sense and is useless. The buffer size is set at build time, and
      defaults to 16 kB.

    - Content-Encoding is not supported, the parameter search will probably
      fail; and load balancing will fall back to Round Robin.

    - Expect: 100-continue is not supported, load balancing will fall back to
      Round Robin.

    - Transfer-Encoding (RFC2616 3.6.1) is only supported in the first chunk.
      If the entire parameter value is not present in the first chunk, the
      selection of server is undefined (actually, defined by how little
      actually appeared in the first chunk).

    - This feature does not support generation of a 100, 411 or 501 response.

    - In some cases, requesting "check_post" MAY attempt to scan the entire
      contents of a message body. Scaning normally terminates when linear
      white space or control characters are found, indicating the end of what
      might be a URL parameter list. This is probably not a concern with SGML
      type message bodies.

  See also : "dispatch", "cookie", "appsession", "transparent" and "http_proxy".


bind [<address>]:<port> [, ...]
bind [<address>]:<port> [, ...] interface <interface>
bind [<address>]:<port> [, ...] transparent
  Define one or several listening addresses and/or ports in a frontend.
  May be used in sections :   defaults | frontend | listen | backend
                                  no   |    yes   |   yes  |   no
  Arguments :
    <address>     is optional and can be a host name, an IPv4 address, an IPv6
                  address, or '*'. It designates the address the frontend will
                  listen on. If unset, all IPv4 addresses of the system will be
                  listened on. The same will apply for '*' or the system's
                  special address "0.0.0.0".

    <port>        is the TCP port number the proxy will listen on. The port is
                  mandatory. Note that in the case of an IPv6 address, the port
                  is always the number after the last colon (':').

    <interface>   is an optional physical interface name. This is currently
                  only supported on Linux. The interface must be a physical
                  interface, not an aliased interface. When specified, all
                  addresses on the same line will only be accepted if the
                  incoming packet physically come through the designated
                  interface. It is also possible to bind multiple frontends to
                  the same address if they are bound to different interfaces.
                  Note that binding to a physical interface requires root
                  privileges.

    transparent   is an optional keyword which is supported only on certain
                  Linux kernels. It indicates that the addresses will be bound
                  even if they do not belong to the local machine. Any packet
                  targetting any of these addresses will be caught just as if
                  the address was locally configured. This normally requires
                  that IP forwarding is enabled. Caution! do not use this with
                  the default address '*', as it would redirect any traffic for
                  the specified port. This keyword is available only when
                  HAProxy is built with USE_LINUX_TPROXY=1.

  It is possible to specify a list of address:port combinations delimited by
  commas. The frontend will then listen on all of these addresses. There is no
  fixed limit to the number of addresses and ports which can be listened on in
  a frontend, as well as there is no limit to the number of "bind" statements
  in a frontend.

  Example :
        listen http_proxy
            bind :80,:443
            bind 10.0.0.1:10080,10.0.0.1:10443

  See also : "source".


bind-process [ all | odd | even | <number 1-32> ] ...
  Limit visibility of an instance to a certain set of processes numbers.
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments :
    all           All process will see this instance. This is the default. It
                  may be used to override a default value.

    odd           This instance will be enabled on processes 1,3,5,...31. This
                  option may be combined with other numbers.

    even          This instance will be enabled on processes 2,4,6,...32. This
                  option may be combined with other numbers. Do not use it
                  with less than 2 processes otherwise some instances might be
                  missing from all processes.

    number        The instance will be enabled on this process number, between
                  1 and 32. You must be careful not to reference a process
                  number greater than the configured global.nbproc, otherwise
                  some instances might be missing from all processes.

  This keyword limits binding of certain instances to certain processes. This
  is useful in order not to have too many processes listening to the same
  ports. For instance, on a dual-core machine, it might make sense to set
  'nbproc 2' in the global section, then distributes the listeners among 'odd'
  and 'even' instances.

  At the moment, it is not possible to reference more than 32 processes using
  this keyword, but this should be more than enough for most setups. Please
  note that 'all' really means all processes and is not limited to the first
  32.

  If some backends are referenced by frontends bound to other processes, the
  backend automatically inherits the frontend's processes.

  Example :
        listen app_ip1
            bind 10.0.0.1:80
            bind_process odd

        listen app_ip2
            bind 10.0.0.2:80
            bind_process even

        listen management
            bind 10.0.0.3:80
            bind_process 1 2 3 4

  See also : "nbproc" in global section.


block { if | unless } <condition>
  Block a layer 7 request if/unless a condition is matched
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    yes   |   yes  |   yes

  The HTTP request will be blocked very early in the layer 7 processing
  if/unless <condition> is matched. A 403 error will be returned if the request
  is blocked. The condition has to reference ACLs (see section 2.3). This is
  typically used to deny access to certain sensible resources if some
  conditions are met or not met. There is no fixed limit to the number of
  "block" statements per instance.

  Example:
        acl invalid_src  src          0.0.0.0/7 224.0.0.0/3
        acl invalid_src  src_port     0:1023
        acl local_dst    hdr(host) -i localhost
        block if invalid_src || local_dst

  See section 2.3 about ACL usage.


capture cookie <name> len <length>
  Capture and log a cookie in the request and in the response.
  May be used in sections :   defaults | frontend | listen | backend
                                  no   |    yes   |   yes  |   no
  Arguments :
    <name>    is the beginning of the name of the cookie to capture. In order
              to match the exact name, simply suffix the name with an equal
              sign ('='). The full name will appear in the logs, which is
              useful with application servers which adjust both the cookie name
              and value (eg: ASPSESSIONXXXXX).

    <length>  is the maximum number of characters to report in the logs, which
              include the cookie name, the equal sign and the value, all in the
              standard "name=value" form. The string will be truncated on the
              right if it exceeds <length>.

  Only the first cookie is captured. Both the "cookie" request headers and the
  "set-cookie" response headers are monitored. This is particularly useful to
  check for application bugs causing session crossing or stealing between
  users, because generally the user's cookies can only change on a login page.

  When the cookie was not presented by the client, the associated log column
  will report "-". When a request does not cause a cookie to be assigned by the
  server, a "-" is reported in the response column.

  The capture is performed in the frontend only because it is necessary that
  the log format does not change for a given frontend depending on the
  backends. This may change in the future. Note that there can be only one
  "capture cookie" statement in a frontend. The maximum capture length is
  configured in the souces by default to 64 characters. It is not possible to
  specify a capture in a "defaults" section.

  Example:
        capture cookie ASPSESSION len 32

  See also : "capture request header", "capture response header" as well as
            section 2.6 about logging.


capture request header <name> len <length>
  Capture and log the first occurrence of the specified request header.
  May be used in sections :   defaults | frontend | listen | backend
                                  no   |    yes   |   yes  |   no
  Arguments :
    <name>    is the name of the header to capture. The header names are not
              case-sensitive, but it is a common practice to write them as they
              appear in the requests, with the first letter of each word in
              upper case. The header name will not appear in the logs, only the
              value is reported, but the position in the logs is respected.

    <length>  is the maximum number of characters to extract from the value and
              report in the logs. The string will be truncated on the right if
              it exceeds <length>.

  Only the first value of the last occurrence of the header is captured. The
  value will be added to the logs between braces ('{}'). If multiple headers
  are captured, they will be delimited by a vertical bar ('|') and will appear
  in the same order they were declared in the configuration. Non-existent
  headers will be logged just as an empty string. Common uses for request
  header captures include the "Host" field in virtual hosting environments, the
  "Content-length" when uploads are supported, "User-agent" to quickly
  differenciate between real users and robots, and "X-Forwarded-For" in proxied
  environments to find where the request came from.

  Note that when capturing headers such as "User-agent", some spaces may be
  logged, making the log analysis more difficult. Thus be careful about what
  you log if you know your log parser is not smart enough to rely on the
  braces.

  There is no limit to the number of captured request headers, but each capture
  is limited to 64 characters. In order to keep log format consistent for a
  same frontend, header captures can only be declared in a frontend. It is not
  possible to specify a capture in a "defaults" section.

  Example:
        capture request header Host len 15
        capture request header X-Forwarded-For len 15
        capture request header Referrer len 15

  See also : "capture cookie", "capture response header" as well as section 2.6
             about logging.


capture response header <name> len <length>
  Capture and log the first occurrence of the specified response header.
  May be used in sections :   defaults | frontend | listen | backend
                                  no   |    yes   |   yes  |   no
  Arguments :
    <name>    is the name of the header to capture. The header names are not
              case-sensitive, but it is a common practice to write them as they
              appear in the response, with the first letter of each word in
              upper case. The header name will not appear in the logs, only the
              value is reported, but the position in the logs is respected.

    <length>  is the maximum number of characters to extract from the value and
              report in the logs. The string will be truncated on the right if
              it exceeds <length>.

  Only the first value of the last occurrence of the header is captured. The
  result will be added to the logs between braces ('{}') after the captured
  request headers. If multiple headers are captured, they will be delimited by
  a vertical bar ('|') and will appear in the same order they were declared in
  the configuration. Non-existent headers will be logged just as an empty
  string. Common uses for response header captures include the "Content-length"
  header which indicates how many bytes are expected to be returned, the
  "Location" header to track redirections.

  There is no limit to the number of captured response headers, but each
  capture is limited to 64 characters. In order to keep log format consistent
  for a same frontend, header captures can only be declared in a frontend. It
  is not possible to specify a capture in a "defaults" section.

  Example:
        capture response header Content-length len 9
        capture response header Location len 15

  See also : "capture cookie", "capture request header" as well as section 2.6
             about logging.


clitimeout <timeout>
  Set the maximum inactivity time on the client side.
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   no
  Arguments :
    <timeout> is the timeout value is specified in milliseconds by default, but
              can be in any other unit if the number is suffixed by the unit,
              as explained at the top of this document.

  The inactivity timeout applies when the client is expected to acknowledge or
  send data. In HTTP mode, this timeout is particularly important to consider
  during the first phase, when the client sends the request, and during the
  response while it is reading data sent by the server. The value is specified
  in milliseconds by default, but can be in any other unit if the number is
  suffixed by the unit, as specified at the top of this document. In TCP mode
  (and to a lesser extent, in HTTP mode), it is highly recommended that the
  client timeout remains equal to the server timeout in order to avoid complex
  situations to debug. It is a good practice to cover one or several TCP packet
  losses by specifying timeouts that are slightly above multiples of 3 seconds
  (eg: 4 or 5 seconds).

  This parameter is specific to frontends, but can be specified once for all in
  "defaults" sections. This is in fact one of the easiest solutions not to
  forget about it. An unspecified timeout results in an infinite timeout, which
  is not recommended. Such a usage is accepted and works but reports a warning
  during startup because it may results in accumulation of expired sessions in
  the system if the system's timeouts are not configured either.

  This parameter is provided for compatibility but is currently deprecated.
  Please use "timeout client" instead.

  See also : "timeout client", "timeout http-request", "timeout server", and
             "srvtimeout".


contimeout <timeout>
  Set the maximum time to wait for a connection attempt to a server to succeed.
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments :
    <timeout> is the timeout value is specified in milliseconds by default, but
              can be in any other unit if the number is suffixed by the unit,
              as explained at the top of this document.

  If the server is located on the same LAN as haproxy, the connection should be
  immediate (less than a few milliseconds). Anyway, it is a good practice to
  cover one or several TCP packet losses by specifying timeouts that are 
  slightly above multiples of 3 seconds (eg: 4 or 5 seconds). By default, the
  connect timeout also presets the queue timeout to the same value if this one
  has not been specified. Historically, the contimeout was also used to set the
  tarpit timeout in a listen section, which is not possible in a pure frontend.

  This parameter is specific to backends, but can be specified once for all in
  "defaults" sections. This is in fact one of the easiest solutions not to
  forget about it. An unspecified timeout results in an infinite timeout, which
  is not recommended. Such a usage is accepted and works but reports a warning
  during startup because it may results in accumulation of failed sessions in
  the system if the system's timeouts are not configured either.

  This parameter is provided for backwards compatibility but is currently
  deprecated. Please use "timeout connect", "timeout queue" or "timeout tarpit"
  instead.

  See also : "timeout connect", "timeout queue", "timeout tarpit",
             "timeout server", "contimeout".


cookie <name> [ rewrite|insert|prefix ] [ indirect ] [ nocache ] [ postonly ] [domain <domain>]
  Enable cookie-based persistence in a backend.
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments :
    <name>    is the name of the cookie which will be monitored, modified or
              inserted in order to bring persistence. This cookie is sent to
              the client via a "Set-Cookie" header in the response, and is
              brought back by the client in a "Cookie" header in all requests.
              Special care should be taken to choose a name which does not
              conflict with any likely application cookie. Also, if the same
              backends are subject to be used by the same clients (eg:
              HTTP/HTTPS), care should be taken to use different cookie names
              between all backends if persistence between them is not desired.

    rewrite   This keyword indicates that the cookie will be provided by the
              server and that haproxy will have to modify its value to set the
              server's identifier in it. This mode is handy when the management
              of complex combinations of "Set-cookie" and "Cache-control"
              headers is left to the application. The application can then
              decide whether or not it is appropriate to emit a persistence
              cookie. Since all responses should be monitored, this mode only
              works in HTTP close mode. Unless the application behaviour is
              very complex and/or broken, it is advised not to start with this
              mode for new deployments. This keyword is incompatible with
              "insert" and "prefix".

    insert    This keyword indicates that the persistence cookie will have to
              be inserted by haproxy in the responses. If the server emits a
              cookie with the same name, it will be replaced anyway. For this
              reason, this mode can be used to upgrade existing configurations
              running in the "rewrite" mode. The cookie will only be a session
              cookie and will not be stored on the client's disk. Due to
              caching effects, it is generally wise to add the "indirect" and
              "nocache" or "postonly" keywords (see below). The "insert"
              keyword is not compatible with "rewrite" and "prefix".

    prefix    This keyword indicates that instead of relying on a dedicated
              cookie for the persistence, an existing one will be completed.
              This may be needed in some specific environments where the client
              does not support more than one single cookie and the application
              already needs it. In this case, whenever the server sets a cookie
              named <name>, it will be prefixed with the server's identifier
              and a delimiter. The prefix will be removed from all client
              requests so that the server still finds the cookie it emitted.
              Since all requests and responses are subject to being modified,
              this mode requires the HTTP close mode. The "prefix" keyword is
              not compatible with "rewrite" and "insert".

    indirect  When this option is specified in insert mode, cookies will only
              be added when the server was not reached after a direct access,
              which means that only when a server is elected after applying a
              load-balancing algorithm, or after a redispatch, then the cookie
              will be inserted. If the client has all the required information
              to connect to the same server next time, no further cookie will
              be inserted. In all cases, when the "indirect" option is used in
              insert mode, the cookie is always removed from the requests
              transmitted to the server. The persistence mechanism then becomes
              totally transparent from the application point of view.

    nocache   This option is recommended in conjunction with the insert mode
              when there is a cache between the client and HAProxy, as it
              ensures that a cacheable response will be tagged non-cacheable if
              a cookie needs to be inserted. This is important because if all
              persistence cookies are added on a cacheable home page for
              instance, then all customers will then fetch the page from an
              outer cache and will all share the same persistence cookie,
              leading to one server receiving much more traffic than others.
              See also the "insert" and "postonly" options.

    postonly  This option ensures that cookie insertion will only be performed
              on responses to POST requests. It is an alternative to the
              "nocache" option, because POST responses are not cacheable, so
              this ensures that the persistence cookie will never get cached.
              Since most sites do not need any sort of persistence before the
              first POST which generally is a login request, this is a very
              efficient method to optimize caching without risking to find a
              persistence cookie in the cache.
              See also the "insert" and "nocache" options.

    domain    This option allows to specify the domain at which a cookie is
              inserted. It requires exactly one paramater: a valid domain
              name.

  There can be only one persistence cookie per HTTP backend, and it can be
  declared in a defaults section. The value of the cookie will be the value
  indicated after the "cookie" keyword in a "server" statement. If no cookie
  is declared for a given server, the cookie is not set.

  Examples :
        cookie JSESSIONID prefix
        cookie SRV insert indirect nocache
        cookie SRV insert postonly indirect

  See also : "appsession", "balance source", "capture cookie", "server".


default_backend <backend>
  Specify the backend to use when no "use_backend" rule has been matched.
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   no
  Arguments :
    <backend> is the name of the backend to use.

  When doing content-switching between frontend and backends using the
  "use_backend" keyword, it is often useful to indicate which backend will be
  used when no rule has matched. It generally is the dynamic backend which
  will catch all undetermined requests.

  The "default_backend" keyword is also supported in TCP mode frontends to
  facilitate the ordering of configurations in frontends and backends,
  eventhough it does not make much more sense in case of TCP due to the fact
  that use_backend currently does not work in TCP mode.

  Example :

        use_backend     dynamic  if  url_dyn
        use_backend     static   if  url_css url_img extension_img
        default_backend dynamic

  See also : "use_backend", "reqsetbe", "reqisetbe"


disabled
  Disable a proxy, frontend or backend.
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments : none

  The "disabled" keyword is used to disable an instance, mainly in order to
  liberate a listening port or to temporarily disable a service. The instance
  will still be created and its configuration will be checked, but it will be
  created in the "stopped" state and will appear as such in the statistics. It
  will not receive any traffic nor will it send any health-checks or logs. It
  is possible to disable many instances at once by adding the "disabled"
  keyword in a "defaults" section.

  See also : "enabled"


enabled
  Enable a proxy, frontend or backend.
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments : none

  The "enabled" keyword is used to explicitly enable an instance, when the
  defaults has been set to "disabled". This is very rarely used.

  See also : "disabled"


errorfile <code> <file>
  Return a file contents instead of errors generated by HAProxy
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments :
    <code>    is the HTTP status code. Currently, HAProxy is capable of
              generating codes 400, 403, 408, 500, 502, 503, and 504.

    <file>    designates a file containing the full HTTP response. It is
              recommended to follow the common practice of appending ".http" to
              the filename so that people do not confuse the response with HTML
              error pages, and to use absolute paths, since files are read
              before any chroot is performed.

  It is important to understand that this keyword is not meant to rewrite
  errors returned by the server, but errors detected and returned by HAProxy.
  This is why the list of supported errors is limited to a small set.

  The files are returned verbatim on the TCP socket. This allows any trick such
  as redirections to another URL or site, as well as tricks to clean cookies,
  force enable or disable caching, etc... The package provides default error
  files returning the same contents as default errors.

  The files should not exceed the configured buffer size (BUFSIZE), which
  generally is 8 or 16 kB, otherwise they will be truncated. It is also wise
  not to put any reference to local contents (eg: images) in order to avoid
  loops between the client and HAProxy when all servers are down, causing an
  error to be returned instead of an image. For better HTTP compliance, it is
  recommended that all header lines end with CR-LF and not LF alone.

  The files are read at the same time as the configuration and kept in memory.
  For this reason, the errors continue to be returned even when the process is
  chrooted, and no file change is considered while the process is running. A
  simple method for developing those files consists in associating them to the
  403 status code and interrogating a blocked URL.

  See also : "errorloc", "errorloc302", "errorloc303"

  Example :
        errorfile 400 /etc/haproxy/errorfiles/400badreq.http
        errorfile 403 /etc/haproxy/errorfiles/403forbid.http
        errorfile 503 /etc/haproxy/errorfiles/503sorry.http


errorloc <code> <url>
errorloc302 <code> <url>
  Return an HTTP redirection to a URL instead of errors generated by HAProxy
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments :
    <code>    is the HTTP status code. Currently, HAProxy is capable of
              generating codes 400, 403, 408, 500, 502, 503, and 504.

    <url>     it is the exact contents of the "Location" header. It may contain
              either a relative URI to an error page hosted on the same site,
              or an absolute URI designating an error page on another site.
              Special care should be given to relative URIs to avoid redirect
              loops if the URI itself may generate the same error (eg: 500).

  It is important to understand that this keyword is not meant to rewrite
  errors returned by the server, but errors detected and returned by HAProxy.
  This is why the list of supported errors is limited to a small set.

  Note that both keyword return the HTTP 302 status code, which tells the
  client to fetch the designated URL using the same HTTP method. This can be
  quite problematic in case of non-GET methods such as POST, because the URL
  sent to the client might not be allowed for something other than GET. To
  workaround this problem, please use "errorloc303" which send the HTTP 303
  status code, indicating to the client that the URL must be fetched with a GET
  request.

  See also : "errorfile", "errorloc303"


errorloc303 <code> <url>
  Return an HTTP redirection to a URL instead of errors generated by HAProxy
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments :
    <code>    is the HTTP status code. Currently, HAProxy is capable of
              generating codes 400, 403, 408, 500, 502, 503, and 504.

    <url>     it is the exact contents of the "Location" header. It may contain
              either a relative URI to an error page hosted on the same site,
              or an absolute URI designating an error page on another site.
              Special care should be given to relative URIs to avoid redirect
              loops if the URI itself may generate the same error (eg: 500).

  It is important to understand that this keyword is not meant to rewrite
  errors returned by the server, but errors detected and returned by HAProxy.
  This is why the list of supported errors is limited to a small set.

  Note that both keyword return the HTTP 303 status code, which tells the
  client to fetch the designated URL using the same HTTP GET method. This
  solves the usual problems associated with "errorloc" and the 302 code. It is
  possible that some very old browsers designed before HTTP/1.1 do not support
  it, but no such problem has been reported till now.

  See also : "errorfile", "errorloc", "errorloc302"


fullconn <conns>
  Specify at what backend load the servers will reach their maxconn
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments :
    <conns>   is the number of connections on the backend which will make the
              servers use the maximal number of connections.

  When a server has a "maxconn" parameter specified, it means that its number
  of concurrent connections will never go higher. Additionally, if it has a
  "minconn" parameter, it indicates a dynamic limit following the backend's
  load. The server will then always accept at least <minconn> connections,
  never more than <maxconn>, and the limit will be on the ramp between both
  values when the backend has less than <conns> concurrent connections. This
  makes it possible to limit the load on the servers during normal loads, but
  push it further for important loads without overloading the servers during
  exceptionnal loads.

  Example :
     # The servers will accept between 100 and 1000 concurrent connections each
     # and the maximum of 1000 will be reached when the backend reaches 10000
     # connections.
     backend dynamic
        fullconn   10000
        server     srv1   dyn1:80 minconn 100 maxconn 1000
        server     srv2   dyn2:80 minconn 100 maxconn 1000

  See also : "maxconn", "server"


grace <time>
  Maintain a proxy operational for some time after a soft stop
  May be used in sections :   defaults | frontend | listen | backend
                                  no   |    yes   |   yes  |   yes
  Arguments :
    <time>    is the time (by default in milliseconds) for which the instance
              will remain operational with the frontend sockets still listening
              when a soft-stop is received via the SIGUSR1 signal.

  This may be used to ensure that the services disappear in a certain order.
  This was designed so that frontends which are dedicated to monitoring by an
  external equipement fail immediately while other ones remain up for the time
  needed by the equipment to detect the failure.

  Note that currently, there is very little benefit in using this parameter,
  and it may in fact complicate the soft-reconfiguration process more than
  simplify it.


http-check disable-on-404
  Enable a maintenance mode upon HTTP/404 response to health-checks
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments : none

  When this option is set, a server which returns an HTTP code 404 will be
  excluded from further load-balancing, but will still receive persistent
  connections. This provides a very convenient method for Web administrators
  to perform a graceful shutdown of their servers. It is also important to note
  that a server which is detected as failed while it was in this mode will not
  generate an alert, just a notice. If the server responds 2xx or 3xx again, it
  will immediately be reinserted into the farm. The status on the stats page
  reports "NOLB" for a server in this mode. It is important to note that this
  option only works in conjunction with the "httpchk" option.

  See also : "option httpchk"


id <value>
  Set a persistent value for proxy ID. Must be unique and larger than 1000, as
  smaller values are reserved for auto-assigned ids.


log global
log <address> <facility> [<level>]
  Enable per-instance logging of events and traffic.
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments :
    global     should be used when the instance's logging parameters are the
               same as the global ones. This is the most common usage. "global"
               replaces <address>, <facility> and <level> with those of the log
               entries found in the "global" section. Only one "log global"
               statement may be used per instance, and this form takes no other
               parameter.

    <address>  indicates where to send the logs. It takes the same format as
               for the "global" section's logs, and can be one of :

               - An IPv4 address optionally followed by a colon (':') and a UDP
                 port. If no port is specified, 514 is used by default (the
                 standard syslog port).

               - A filesystem path to a UNIX domain socket, keeping in mind
                 considerations for chroot (be sure the path is accessible
                 inside the chroot) and uid/gid (be sure the path is
                 appropriately writeable).

    <facility> must be one of the 24 standard syslog facilities :

                 kern   user   mail   daemon auth   syslog lpr    news
                 uucp   cron   auth2  ftp    ntp    audit  alert  cron2
                 local0 local1 local2 local3 local4 local5 local6 local7

    <level>    is optional and can be specified to filter outgoing messages. By
               default, all messages are sent. If a level is specified, only
               messages with a severity at least as important as this level
               will be sent. 8 levels are known :

                 emerg  alert  crit   err    warning notice info  debug

  Note that up to two "log" entries may be specified per instance. However, if
  "log global" is used and if the "global" section already contains 2 log
  entries, then additional log entries will be ignored.

  Also, it is important to keep in mind that it is the frontend which decides
  what to log from a connection, and that in case of content switching, the log
  entries from the backend will be ignored. Connections are logged at level
  "info".

  However, backend log declaration define how and where servers status changes
  will be logged. Level "notice" will be used to indicate a server going up,
  "warning" will be used for termination signals and definitive service
  termination, and "alert" will be used for when a server goes down.

  Note : According to RFC3164, messages are truncated to 1024 bytes before
         being emitted.

  Example :
    log global
    log 127.0.0.1:514 local0 notice


maxconn <conns>
  Fix the maximum number of concurrent connections on a frontend
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   no
  Arguments :
    <conns>   is the maximum number of concurrent connections the frontend will
              accept to serve. Excess connections will be queued by the system
              in the socket's listen queue and will be served once a connection
              closes.

  If the system supports it, it can be useful on big sites to raise this limit
  very high so that haproxy manages connection queues, instead of leaving the
  clients with unanswered connection attempts. This value should not exceed the
  global maxconn. Also, keep in mind that a connection contains two buffers
  of 8kB each, as well as some other data resulting in about 17 kB of RAM being
  consumed per established connection. That means that a medium system equipped
  with 1GB of RAM can withstand around 40000-50000 concurrent connections if
  properly tuned.

  Also, when <conns> is set to large values, it is possible that the servers
  are not sized to accept such loads, and for this reason it is generally wise
  to assign them some reasonable connection limits.

  See also : "server", global section's "maxconn", "fullconn"


mode { tcp|http|health }
  Set the running mode or protocol of the instance
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments :
    tcp       The instance will work in pure TCP mode. A full-duplex connection
              will be established between clients and servers, and no layer 7
              examination will be performed. This is the default mode. It
              should be used for SSL, SSH, SMTP, ...

    http      The instance will work in HTTP mode. The client request will be
              analyzed in depth before connecting to any server. Any request
              which is not RFC-compliant will be rejected. Layer 7 filtering,
              processing and switching will be possible. This is the mode which
              brings HAProxy most of its value.

    health    The instance will work in "health" mode. It will just reply "OK"
              to incoming connections and close the connection. Nothing will be
              logged. This mode is used to reply to external components health
              checks. This mode is deprecated and should not be used anymore as
              it is possible to do the same and even better by combining TCP or
              HTTP modes with the "monitor" keyword.

   When doing content switching, it is mandatory that the frontend and the
   backend are in the same mode (generally HTTP), otherwise the configuration
   will be refused.

   Example :
     defaults http_instances
         mode http

   See also : "monitor", "monitor-net"


monitor fail [if | unless] <condition>
  Add a condition to report a failure to a monitor HTTP request.
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    yes   |   yes  |   no
  Arguments :
    if <cond>     the monitor request will fail if the condition is satisfied,
                  and will succeed otherwise. The condition should describe a
                  combinated test which must induce a failure if all conditions
                  are met, for instance a low number of servers both in a
                  backend and its backup.

    unless <cond> the monitor request will succeed only if the condition is
                  satisfied, and will fail otherwise. Such a condition may be
                  based on a test on the presence of a minimum number of active
                  servers in a list of backends.

  This statement adds a condition which can force the response to a monitor
  request to report a failure. By default, when an external component queries
  the URI dedicated to monitoring, a 200 response is returned. When one of the
  conditions above is met, haproxy will return 503 instead of 200. This is
  very useful to report a site failure to an external component which may base
  routing advertisements between multiple sites on the availability reported by
  haproxy. In this case, one would rely on an ACL involving the "nbsrv"
  criterion. Note that "monitor fail" only works in HTTP mode.

  Example:
     frontend www
        mode http
        acl site_dead nbsrv(dynamic) lt 2
        acl site_dead nbsrv(static)  lt 2
        monitor-uri   /site_alive
        monitor fail  if site_dead

  See also : "monitor-net", "monitor-uri"


monitor-net <source>
  Declare a source network which is limited to monitor requests
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   no
  Arguments :
    <source>  is the source IPv4 address or network which will only be able to
              get monitor responses to any request. It can be either an IPv4
              address, a host name, or an address followed by a slash ('/')
              followed by a mask.

  In TCP mode, any connection coming from a source matching <source> will cause
  the connection to be immediately closed without any log. This allows another
  equipement to probe the port and verify that it is still listening, without
  forwarding the connection to a remote server.

  In HTTP mode, a connection coming from a source matching <source> will be
  accepted, the following response will be sent without waiting for a request,
  then the connection will be closed : "HTTP/1.0 200 OK". This is normally
  enough for any front-end HTTP probe to detect that the service is UP and
  running without forwarding the request to a backend server.

  Monitor requests are processed very early. It is not possible to block nor
  divert them using ACLs. They cannot be logged either, and it is the intended
  purpose. They are only used to report HAProxy's health to an upper component,
  nothing more. Right now, it is not possible to set failure conditions on
  requests caught by "monitor-net".

  Example :
    # addresses .252 and .253 are just probing us.
    frontend www
        monitor-net 192.168.0.252/31

  See also : "monitor fail", "monitor-uri"


monitor-uri <uri>
  Intercept a URI used by external components' monitor requests
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   no
  Arguments :
    <uri>     is the exact URI which we want to intercept to return HAProxy's
              health status instead of forwarding the request.

  When an HTTP request referencing <uri> will be received on a frontend,
  HAProxy will not forward it nor log it, but instead will return either
  "HTTP/1.0 200 OK" or "HTTP/1.0 503 Service unavailable", depending on failure
  conditions defined with "monitor fail". This is normally enough for any
  front-end HTTP probe to detect that the service is UP and running without
  forwarding the request to a backend server. Note that the HTTP method, the
  version and all headers are ignored, but the request must at least be valid
  at the HTTP level. This keyword may only be used with an HTTP-mode frontend.

  Monitor requests are processed very early. It is not possible to block nor
  divert them using ACLs. They cannot be logged either, and it is the intended
  purpose. They are only used to report HAProxy's health to an upper component,
  nothing more. However, it is possible to add any number of conditions using
  "monitor fail" and ACLs so that the result can be adjusted to whatever check
  can be imagined (most often the number of available servers in a backend).

  Example :
    # Use /haproxy_test to report haproxy's status
    frontend www
        mode http
        monitor-uri /haproxy_test

  See also : "monitor fail", "monitor-net"


option abortonclose
no option abortonclose
  Enable or disable early dropping of aborted requests pending in queues.
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |     no   |   yes  |   yes
  Arguments : none

  In presence of very high loads, the servers will take some time to respond.
  The per-instance connection queue will inflate, and the response time will
  increase respective to the size of the queue times the average per-session
  response time. When clients will wait for more than a few seconds, they will
  often hit the "STOP" button on their browser, leaving a useless request in
  the queue, and slowing down other users, and the servers as well, because the
  request will eventually be served, then aborted at the first error
  encountered while delivering the response.

  As there is no way to distinguish between a full STOP and a simple output
  close on the client side, HTTP agents should be conservative and consider
  that the client might only have closed its output channel while waiting for
  the response. However, this introduces risks of congestion when lots of users
  do the same, and is completely useless nowadays because probably no client at
  all will close the session while waiting for the response. Some HTTP agents
  support this behaviour (Squid, Apache, HAProxy), and others do not (TUX, most 
  hardware-based load balancers). So the probability for a closed input channel
  to represent a user hitting the "STOP" button is close to 100%, and the risk
  of being the single component to break rare but valid traffic is extremely
  low, which adds to the temptation to be able to abort a session early while
  still not served and not pollute the servers.

  In HAProxy, the user can choose the desired behaviour using the option
  "abortonclose". By default (without the option) the behaviour is HTTP
  compliant and aborted requests will be served. But when the option is
  specified, a session with an incoming channel closed will be aborted while
  it is still possible, either pending in the queue for a connection slot, or
  during the connection establishment if the server has not yet acknowledged
  the connection request. This considerably reduces the queue size and the load
  on saturated servers when users are tempted to click on STOP, which in turn
  reduces the response time for other users. 

  If this option has been enabled in a "defaults" section, it can be disabled
  in a specific instance by prepending the "no" keyword before it.

  See also : "timeout queue" and server's "maxconn" and "maxqueue" parameters


option accept-invalid-http-request
no option accept-invalid-http-request
  Enable or disable relaxing of HTTP request parsing
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   no
  Arguments : none

  By default, HAProxy complies with RFC2616 in terms of message parsing. This
  means that invalid characters in header names are not permitted and cause an
  error to be returned to the client. This is the desired behaviour as such
  forbidden characters are essentially used to build attacks exploiting server
  weaknesses, and bypass security filtering. Sometimes, a buggy browser or
  server will emit invalid header names for whatever reason (configuration,
  implementation) and the issue will not be immediately fixed. In such a case,
  it is possible to relax HAProxy's header name parser to accept any character
  even if that does not make sense, by specifying this option.

  This option should never be enabled by default as it hides application bugs
  and open security breaches. It should only be deployed after a problem has
  been confirmed.

  When this option is enabled, erroneous header names will still be accepted in
  requests, but the complete request will be captured in order to permit later
  analysis using the "show errors" request on the UNIX stats socket. Doing this
  also helps confirming that the issue has been solved.

  If this option has been enabled in a "defaults" section, it can be disabled
  in a specific instance by prepending the "no" keyword before it.

  See also : "option accept-invalid-http-response" and "show errors" on the
             stats socket.


option accept-invalid-http-response
no option accept-invalid-http-response
  Enable or disable relaxing of HTTP response parsing
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |     no   |   yes  |   yes
  Arguments : none

  By default, HAProxy complies with RFC2616 in terms of message parsing. This
  means that invalid characters in header names are not permitted and cause an
  error to be returned to the client. This is the desired behaviour as such
  forbidden characters are essentially used to build attacks exploiting server
  weaknesses, and bypass security filtering. Sometimes, a buggy browser or
  server will emit invalid header names for whatever reason (configuration,
  implementation) and the issue will not be immediately fixed. In such a case,
  it is possible to relax HAProxy's header name parser to accept any character
  even if that does not make sense, by specifying this option.

  This option should never be enabled by default as it hides application bugs
  and open security breaches. It should only be deployed after a problem has
  been confirmed.

  When this option is enabled, erroneous header names will still be accepted in
  responses, but the complete response will be captured in order to permit
  later analysis using the "show errors" request on the UNIX stats socket.
  Doing this also helps confirming that the issue has been solved.

  If this option has been enabled in a "defaults" section, it can be disabled
  in a specific instance by prepending the "no" keyword before it.

  See also : "option accept-invalid-http-request" and "show errors" on the
             stats socket.


option allbackups
no option allbackups
  Use either all backup servers at a time or only the first one
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |     no   |   yes  |   yes
  Arguments : none

  By default, the first operational backup server gets all traffic when normal
  servers are all down. Sometimes, it may be preferred to use multiple backups
  at once, because one will not be enough. When "option allbackups" is enabled,
  the load balancing will be performed among all backup servers when all normal
  ones are unavailable. The same load balancing algorithm will be used and the
  servers' weights will be respected. Thus, there will not be any priority
  order between the backup servers anymore.

  This option is mostly used with static server farms dedicated to return a
  "sorry" page when an application is completely offline.

  If this option has been enabled in a "defaults" section, it can be disabled
  in a specific instance by prepending the "no" keyword before it.


option checkcache
no option checkcache
  Analyze all server responses and block requests with cachable cookies
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |     no   |   yes  |   yes
  Arguments : none

  Some high-level frameworks set application cookies everywhere and do not
  always let enough control to the developer to manage how the responses should
  be cached. When a session cookie is returned on a cachable object, there is a
  high risk of session crossing or stealing between users traversing the same
  caches. In some situations, it is better to block the response than to let
  some sensible session information go in the wild.

  The option "checkcache" enables deep inspection of all server responses for
  strict compliance with HTTP specification in terms of cachability. It
  carefully checks "Cache-control", "Pragma" and "Set-cookie" headers in server
  response to check if there's a risk of caching a cookie on a client-side
  proxy. When this option is enabled, the only responses which can be delivered
  to the client are :
    - all those without "Set-Cookie" header ;
    - all those with a return code other than 200, 203, 206, 300, 301, 410,
      provided that the server has not set a "Cache-control: public" header ;
    - all those that come from a POST request, provided that the server has not
      set a 'Cache-Control: public' header ;
    - those with a 'Pragma: no-cache' header
    - those with a 'Cache-control: private' header
    - those with a 'Cache-control: no-store' header
    - those with a 'Cache-control: max-age=0' header
    - those with a 'Cache-control: s-maxage=0' header
    - those with a 'Cache-control: no-cache' header
    - those with a 'Cache-control: no-cache="set-cookie"' header
    - those with a 'Cache-control: no-cache="set-cookie,' header
      (allowing other fields after set-cookie)

  If a response doesn't respect these requirements, then it will be blocked
  just as if it was from an "rspdeny" filter, with an "HTTP 502 bad gateway".
  The session state shows "PH--" meaning that the proxy blocked the response
  during headers processing. Additionnaly, an alert will be sent in the logs so
  that admins are informed that there's something to be fixed.

  Due to the high impact on the application, the application should be tested
  in depth with the option enabled before going to production. It is also a
  good practice to always activate it during tests, even if it is not used in
  production, as it will report potentially dangerous application behaviours.

  If this option has been enabled in a "defaults" section, it can be disabled
  in a specific instance by prepending the "no" keyword before it.


option clitcpka
no option clitcpka
  Enable or disable the sending of TCP keepalive packets on the client side
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   no
  Arguments : none

  When there is a firewall or any session-aware component between a client and
  a server, and when the protocol involves very long sessions with long idle
  periods (eg: remote desktops), there is a risk that one of the intermediate
  components decides to expire a session which has remained idle for too long.

  Enabling socket-level TCP keep-alives makes the system regularly send packets
  to the other end of the connection, leaving it active. The delay between
  keep-alive probes is controlled by the system only and depends both on the
  operating system and its tuning parameters.

  It is important to understand that keep-alive packets are neither emitted nor
  received at the application level. It is only the network stacks which sees
  them. For this reason, even if one side of the proxy already uses keep-alives
  to maintain its connection alive, those keep-alive packets will not be
  forwarded to the other side of the proxy.

  Please note that this has nothing to do with HTTP keep-alive.

  Using option "clitcpka" enables the emission of TCP keep-alive probes on the
  client side of a connection, which should help when session expirations are
  noticed between HAProxy and a client.

  If this option has been enabled in a "defaults" section, it can be disabled
  in a specific instance by prepending the "no" keyword before it.

  See also : "option srvtcpka", "option tcpka"


option contstats
  Enable continuous traffic statistics updates
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   no
  Arguments : none

  By default, counters used for statistics calculation are incremented
  only when a session finishes. It works quite well when serving small
  objects, but with big ones (for example large images or archives) or
  with A/V streaming, a graph generated from haproxy counters looks like
  a hedgehog. With this option enabled counters get incremented continuously,
  during a whole session. Recounting touches a hotpath directly so
  it is not enabled by default, as it has small performance impact (~0.5%).


option dontlognull
no option dontlognull
  Enable or disable logging of null connections
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   no
  Arguments : none

  In certain environments, there are components which will regularly connect to
  various systems to ensure that they are still alive. It can be the case from
  another load balancer as well as from monitoring systems. By default, even a
  simple port probe or scan will produce a log. If those connections pollute
  the logs too much, it is possible to enable option "dontlognull" to indicate
  that a connection on which no data has been transferred will not be logged,
  which typically corresponds to those probes.

  It is generally recommended not to use this option in uncontrolled
  environments (eg: internet), otherwise scans and other malicious activities
  would not be logged.

  If this option has been enabled in a "defaults" section, it can be disabled
  in a specific instance by prepending the "no" keyword before it.

  See also : "log", "monitor-net", "monitor-uri" and section 2.6 about logging.


option forceclose
no option forceclose
  Enable or disable active connection closing after response is transferred.
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |     no   |   yes  |   yes
  Arguments : none

  Some HTTP servers do not necessarily close the connections when they receive
  the "Connection: close" set by "option httpclose", and if the client does not
  close either, then the connection remains open till the timeout expires. This
  causes high number of simultaneous connections on the servers and shows high
  global session times in the logs.

  When this happens, it is possible to use "option forceclose". It will
  actively close the outgoing server channel as soon as the server begins to
  reply and only if the request buffer is empty. Note that this should NOT be
  used if CONNECT requests are expected between the client and the server. This
  option implicitly enables the "httpclose" option.

  If this option has been enabled in a "defaults" section, it can be disabled
  in a specific instance by prepending the "no" keyword before it.

  See also : "option httpclose"


option forwardfor [ except <network> ] [ header <name> ]
  Enable insertion of the X-Forwarded-For header to requests sent to servers
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments :
    <network> is an optional argument used to disable this option for sources
              matching <network>
    <name>    an optional argument to specify a different "X-Forwarded-For"
              header name.  

  Since HAProxy works in reverse-proxy mode, the servers see its IP address as
  their client address. This is sometimes annoying when the client's IP address
  is expected in server logs. To solve this problem, the well-known HTTP header
  "X-Forwarded-For" may be added by HAProxy to all requests sent to the server.
  This header contains a value representing the client's IP address. Since this
  header is always appended at the end of the existing header list, the server
  must be configured to always use the last occurrence of this header only. See
  the server's manual to find how to enable use of this standard header. Note
  that only the last occurrence of the header must be used, since it is really
  possible that the client has already brought one.

  The keyword "header" may be used to supply a different header name to replace 
  the default "X-Forwarded-For". This can be useful where you might already
  have a "X-Forwarded-For" header from a different application (eg: stunnel), 
  and you need preserve it. Also if your backend server doesn't use the 
  "X-Forwarded-For" header and requires different one (eg: Zeus Web Servers
  require "X-Cluster-Client-IP").

  Sometimes, a same HAProxy instance may be shared between a direct client
  access and a reverse-proxy access (for instance when an SSL reverse-proxy is
  used to decrypt HTTPS traffic). It is possible to disable the addition of the
  header for a known source address or network by adding the "except" keyword
  followed by the network address. In this case, any source IP matching the
  network will not cause an addition of this header. Most common uses are with
  private networks or 127.0.0.1.

  This option may be specified either in the frontend or in the backend. If at
  least one of them uses it, the header will be added. Note that the backend's
  setting of the header subargument takes precedence over the frontend's if
  both are defined.

  It is important to note that as long as HAProxy does not support keep-alive
  connections, only the first request of a connection will receive the header.
  For this reason, it is important to ensure that "option httpclose" is set
  when using this option.

  Examples :
    # Public HTTP address also used by stunnel on the same machine
    frontend www
        mode http
        option forwardfor except 127.0.0.1  # stunnel already adds the header

    # Those servers want the IP Address in X-Client
    backend www
        mode http
        option forwardfor header X-Client

  See also : "option httpclose"


option originalto [ except <network> ] [ header <name> ]
  Enable insertion of the X-Original-To header to requests sent to servers
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments :
    <network> is an optional argument used to disable this option for sources
              matching <network>
    <name>    an optional argument to specify a different "X-Original-To"
              header name.

  Since HAProxy can work in transparent mode, every request from a client can
  be redirected to the proxy and HAProxy itself can proxy every request to a
  complex SQUID environment and the destination host from SO_ORIGINAL_DST will
  be lost. This is annoying when you want access rules based on destination ip
  addresses. To solve this problem, a new HTTP header "X-Original-To" may be
  added by HAProxy to all requests sent to the server. This header contains a
  value representing the original destination IP address. Since this must be
  configured to always use the last occurrence of this header only. Note that
  only the last occurrence of the header must be used, since it is really
  possible that the client has already brought one.

  The keyword "header" may be used to supply a different header name to replace
  the default "X-Original-To". This can be useful where you might already
  have a "X-Original-To" header from a different application, and you need
  preserve it. Also if your backend server doesn't use the "X-Original-To"
  header and requires different one.

  Sometimes, a same HAProxy instance may be shared between a direct client
  access and a reverse-proxy access (for instance when an SSL reverse-proxy is
  used to decrypt HTTPS traffic). It is possible to disable the addition of the
  header for a known source address or network by adding the "except" keyword
  followed by the network address. In this case, any source IP matching the
  network will not cause an addition of this header. Most common uses are with
  private networks or 127.0.0.1.

  This option may be specified either in the frontend or in the backend. If at
  least one of them uses it, the header will be added. Note that the backend's
  setting of the header subargument takes precedence over the frontend's if
  both are defined.

  It is important to note that as long as HAProxy does not support keep-alive
  connections, only the first request of a connection will receive the header.
  For this reason, it is important to ensure that "option httpclose" is set
  when using this option.

  Examples :
    # Original Destination address
    frontend www
        mode http
        option originalto except 127.0.0.1

    # Those servers want the IP Address in X-Client-Dst
    backend www
        mode http
        option originalto header X-Client-Dst

  See also : "option httpclose"


option http_proxy
no option http_proxy
  Enable or disable plain HTTP proxy mode
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments : none

  It sometimes happens that people need a pure HTTP proxy which understands
  basic proxy requests without caching nor any fancy feature. In this case,
  it may be worth setting up an HAProxy instance with the "option http_proxy"
  set. In this mode, no server is declared, and the connection is forwarded to
  the IP address and port found in the URL after the "http://" scheme.

  No host address resolution is performed, so this only works when pure IP
  addresses are passed. Since this option's usage perimeter is rather limited,
  it will probably be used only by experts who know they need exactly it. Last,
  if the clients are susceptible of sending keep-alive requests, it will be
  needed to add "option http_close" to ensure that all requests will correctly
  be analyzed.

  If this option has been enabled in a "defaults" section, it can be disabled
  in a specific instance by prepending the "no" keyword before it.

  Example :
    # this backend understands HTTP proxy requests and forwards them directly.
    backend direct_forward
        option httpclose
        option http_proxy

  See also : "option httpclose"


option httpchk
option httpchk <uri>
option httpchk <method> <uri>
option httpchk <method> <uri> <version>
  Enable HTTP protocol to check on the servers health
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments :
    <method>  is the optional HTTP method used with the requests. When not set,
              the "OPTIONS" method is used, as it generally requires low server
              processing and is easy to filter out from the logs. Any method
              may be used, though it is not recommended to invent non-standard
              ones.

    <uri>     is the URI referenced in the HTTP requests. It defaults to " / "
              which is accessible by default on almost any server, but may be
              changed to any other URI. Query strings are permitted.

    <version> is the optional HTTP version string. It defaults to "HTTP/1.0"
              but some servers might behave incorrectly in HTTP 1.0, so turning
              it to HTTP/1.1 may sometimes help. Note that the Host field is
              mandatory in HTTP/1.1, and as a trick, it is possible to pass it
              after "\r\n" following the version string.

  By default, server health checks only consist in trying to establish a TCP
  connection. When "option httpchk" is specified, a complete HTTP request is
  sent once the TCP connection is established, and responses 2xx and 3xx are
  considered valid, while all other ones indicate a server failure, including
  the lack of any response.

  The port and interval are specified in the server configuration.

  This option does not necessarily require an HTTP backend, it also works with
  plain TCP backends. This is particularly useful to check simple scripts bound
  to some dedicated ports using the inetd daemon.

  Examples :
      # Relay HTTPS traffic to Apache instance and check service availability
      # using HTTP request "OPTIONS * HTTP/1.1" on port 80.
      backend https_relay
          mode tcp
          option httpchk OPTIONS * HTTP/1.1\r\nHost:\ www
          server apache1 192.168.1.1:443 check port 80

  See also : "option ssl-hello-chk", "option smtpchk", "http-check" and the
             "check", "port" and "interval" server options.


option httpclose
no option httpclose
  Enable or disable passive HTTP connection closing
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments : none

  As stated in section 2.1, HAProxy does not yes support the HTTP keep-alive
  mode. So by default, if a client communicates with a server in this mode, it
  will only analyze, log, and process the first request of each connection. To
  workaround this limitation, it is possible to specify "option httpclose". It
  will check if a "Connection: close" header is already set in each direction,
  and will add one if missing. Each end should react to this by actively
  closing the TCP connection after each transfer, thus resulting in a switch to
  the HTTP close mode. Any "Connection" header different from "close" will also
  be removed.

  It seldom happens that some servers incorrectly ignore this header and do not
  close the connection eventough they reply "Connection: close". For this
  reason, they are not compatible with older HTTP 1.0 browsers. If this
  happens it is possible to use the "option forceclose" which actively closes
  the request connection once the server responds.

  This option may be set both in a frontend and in a backend. It is enabled if
  at least one of the frontend or backend holding a connection has it enabled.
  If "option forceclose" is specified too, it has precedence over "httpclose".

  If this option has been enabled in a "defaults" section, it can be disabled
  in a specific instance by prepending the "no" keyword before it.

  See also : "option forceclose"


option httplog
  Enable logging of HTTP request, session state and timers
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments : none

  By default, the log output format is very poor, as it only contains the
  source and destination addresses, and the instance name. By specifying
  "option httplog", each log line turns into a much richer format including,
  but not limited to, the HTTP request, the connection timers, the session
  status, the connections numbers, the captured headers and cookies, the
  frontend, backend and server name, and of course the source address and
  ports.

  This option may be set either in the frontend or the backend.

  See also :  section 2.6 about logging.


option logasap
no option logasap
  Enable or disable early logging of HTTP requests
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   no
  Arguments : none

  By default, HTTP requests are logged upon termination so that the total
  transfer time and the number of bytes appear in the logs. When large objects
  are being transferred, it may take a while before the request appears in the
  logs. Using "option logasap", the request gets logged as soon as the server
  sends the complete headers. The only missing information in the logs will be
  the total number of bytes which will indicate everything except the amount
  of data transferred, and the total time which will not take the transfer
  time into account. In such a situation, it's a good practice to capture the
  "Content-Length" response header so that the logs at least indicate how many
  bytes are expected to be transferred.

  Examples :
      listen http_proxy 0.0.0.0:80
          mode http
          option httplog
          option logasap
          log 192.168.2.200 local3

    >>> Feb  6 12:14:14 localhost \
          haproxy[14389]: 10.0.1.2:33317 [06/Feb/2009:12:14:14.655] http-in \
          static/srv1 9/10/7/14/+30 200 +243 - - ---- 3/1/1/1/0 1/0 \
          "GET /image.iso HTTP/1.0"

  See also : "option httplog", "capture response header", and section 2.6 about
             logging.


option nolinger
no option nolinger
  Enable or disable immediate session ressource cleaning after close
  May be used in sections:    defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments : none

  When clients or servers abort connections in a dirty way (eg: they are
  physically disconnected), the session timeouts triggers and the session is
  closed. But it will remain in FIN_WAIT1 state for some time in the system,
  using some resources and possibly limiting the ability to establish newer
  connections.

  When this happens, it is possible to activate "option nolinger" which forces
  the system to immediately remove any socket's pending data on close. Thus,
  the session is instantly purged from the system's tables. This usually has
  side effects such as increased number of TCP resets due to old retransmits
  getting immediately rejected. Some firewalls may sometimes complain about
  this too.

  For this reason, it is not recommended to use this option when not absolutely
  needed. You know that you need it when you have thousands of FIN_WAIT1
  sessions on your system (TIME_WAIT ones do not count).

  This option may be used both on frontends and backends, depending on the side
  where it is required. Use it on the frontend for clients, and on the backend
  for servers.

  If this option has been enabled in a "defaults" section, it can be disabled
  in a specific instance by prepending the "no" keyword before it.


option persist
no option persist
  Enable or disable forced persistence on down servers
  May be used in sections:    defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments : none

  When an HTTP request reaches a backend with a cookie which references a dead
  server, by default it is redispatched to another server. It is possible to
  force the request to be sent to the dead server first using "option persist"
  if absolutely needed. A common use case is when servers are under extreme
  load and spend their time flapping. In this case, the users would still be
  directed to the server they opened the session on, in the hope they would be
  correctly served. It is recommended to use "option redispatch" in conjunction
  with this option so that in the event it would not be possible to connect to
  the server at all (server definitely dead), the client would finally be
  redirected to another valid server.

  If this option has been enabled in a "defaults" section, it can be disabled
  in a specific instance by prepending the "no" keyword before it.

  See also : "option redispatch", "retries"


option redispatch
no option redispatch
  Enable or disable session redistribution in case of connection failure
  May be used in sections:    defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments : none

  In HTTP mode, if a server designated by a cookie is down, clients may
  definitely stick to it because they cannot flush the cookie, so they will not
  be able to access the service anymore.

  Specifying "option redispatch" will allow the proxy to break their
  persistence and redistribute them to a working server.

  It also allows to retry last connection to another server in case of multiple
  connection failures. Of course, it requires having "retries" set to a nonzero
  value.
  
  This form is the preferred form, which replaces both the "redispatch" and
  "redisp" keywords.

  If this option has been enabled in a "defaults" section, it can be disabled
  in a specific instance by prepending the "no" keyword before it.

  See also : "redispatch", "retries"


option smtpchk
option smtpchk <hello> <domain>
  Use SMTP health checks for server testing
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments : 
    <hello>   is an optional argument. It is the "hello" command to use. It can
              be either "HELO" (for SMTP) or "EHLO" (for ESTMP). All other
              values will be turned into the default command ("HELO").

    <domain>  is the domain name to present to the server. It may only be
              specified (and is mandatory) if the hello command has been
              specified. By default, "localhost" is used.

  When "option smtpchk" is set, the health checks will consist in TCP
  connections followed by an SMTP command. By default, this command is
  "HELO localhost". The server's return code is analyzed and only return codes
  starting with a "2" will be considered as valid. All other responses,
  including a lack of response will constitute an error and will indicate a
  dead server.

  This test is meant to be used with SMTP servers or relays. Depending on the
  request, it is possible that some servers do not log each connection attempt,
  so you may want to experiment to improve the behaviour. Using telnet on port
  25 is often easier than adjusting the configuration.

  Most often, an incoming SMTP server needs to see the client's IP address for
  various purposes, including spam filtering, anti-spoofing and logging. When
  possible, it is often wise to masquerade the client's IP address when
  connecting to the server using the "usesrc" argument of the "source" keyword,
  which requires the cttproxy feature to be compiled in.

  Example :
        option smtpchk HELO mydomain.org

  See also : "option httpchk", "source"


option splice-auto
no option splice-auto
  Enable or disable automatic kernel acceleration on sockets in both directions
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments : none

  When this option is enabled either on a frontend or on a backend, haproxy
  will automatically evaluate the opportunity to use kernel tcp splicing to
  forward data between the client and the server, in either direction. Haproxy
  uses heuristics to estimate if kernel splicing might improve performance or
  not. Both directions are handled independantly. Note that the heuristics used
  are not much aggressive in order to limit excessive use of splicing. This
  option requires splicing to be enabled at compile time, and may be globally
  disabled with the global option "nosplice". Since splice uses pipes, using it
  requires that there are enough spare pipes.

  Important note: kernel-based TCP splicing is a Linux-specific feature which
  first appeared in kernel 2.6.25. It offers kernel-based acceleration to
  transfer data between sockets without copying these data to user-space, thus
  providing noticeable performance gains and CPU cycles savings. Since many
  early implementations are buggy, corrupt data and/or are inefficient, this
  feature is not enabled by default, and it should be used with extreme care.
  While it is not possible to detect the correctness of an implementation,
  2.6.29 is the first version offering a properly working implementation. In
  case of doubt, splicing may be globally disabled using the global "nosplice"
  keyword.

  Example :
        option splice-auto

  If this option has been enabled in a "defaults" section, it can be disabled
  in a specific instance by prepending the "no" keyword before it.

  See also : "option splice-request", "option splice-response", and global
             options "nosplice" and "maxpipes"


option splice-request
no option splice-request
  Enable or disable automatic kernel acceleration on sockets for requests
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments : none

  When this option is enabled either on a frontend or on a backend, haproxy
  will user kernel tcp splicing whenever possible to forward data going from
  the client to the server. It might still use the recv/send scheme if there
  are no spare pipes left. This option requires splicing to be enabled at
  compile time, and may be globally disabled with the global option "nosplice".
  Since splice uses pipes, using it requires that there are enough spare pipes.

  Important note: see "option splice-auto" for usage limitations.

  Example :
        option splice-request

  If this option has been enabled in a "defaults" section, it can be disabled
  in a specific instance by prepending the "no" keyword before it.

  See also : "option splice-auto", "option splice-response", and global options
             "nosplice" and "maxpipes"


option splice-response
no option splice-response
  Enable or disable automatic kernel acceleration on sockets for responses
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments : none

  When this option is enabled either on a frontend or on a backend, haproxy
  will user kernel tcp splicing whenever possible to forward data going from
  the server to the client. It might still use the recv/send scheme if there
  are no spare pipes left. This option requires splicing to be enabled at
  compile time, and may be globally disabled with the global option "nosplice".
  Since splice uses pipes, using it requires that there are enough spare pipes.

  Important note: see "option splice-auto" for usage limitations.

  Example :
        option splice-response

  If this option has been enabled in a "defaults" section, it can be disabled
  in a specific instance by prepending the "no" keyword before it.

  See also : "option splice-auto", "option splice-request", and global options
             "nosplice" and "maxpipes"


option srvtcpka
no option srvtcpka
  Enable or disable the sending of TCP keepalive packets on the server side
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments : none

  When there is a firewall or any session-aware component between a client and
  a server, and when the protocol involves very long sessions with long idle
  periods (eg: remote desktops), there is a risk that one of the intermediate
  components decides to expire a session which has remained idle for too long.

  Enabling socket-level TCP keep-alives makes the system regularly send packets
  to the other end of the connection, leaving it active. The delay between
  keep-alive probes is controlled by the system only and depends both on the
  operating system and its tuning parameters.

  It is important to understand that keep-alive packets are neither emitted nor
  received at the application level. It is only the network stacks which sees
  them. For this reason, even if one side of the proxy already uses keep-alives
  to maintain its connection alive, those keep-alive packets will not be
  forwarded to the other side of the proxy.

  Please note that this has nothing to do with HTTP keep-alive.

  Using option "srvtcpka" enables the emission of TCP keep-alive probes on the
  server side of a connection, which should help when session expirations are
  noticed between HAProxy and a server.

  If this option has been enabled in a "defaults" section, it can be disabled
  in a specific instance by prepending the "no" keyword before it.

  See also : "option clitcpka", "option tcpka"


option ssl-hello-chk
  Use SSLv3 client hello health checks for server testing
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments : none

  When some SSL-based protocols are relayed in TCP mode through HAProxy, it is
  possible to test that the server correctly talks SSL instead of just testing
  that it accepts the TCP connection. When "option ssl-hello-chk" is set, pure
  SSLv3 client hello messages are sent once the connection is established to
  the server, and the response is analyzed to find an SSL server hello message.
  The server is considered valid only when the response contains this server
  hello message.

  All servers tested till there correctly reply to SSLv3 client hello messages,
  and most servers tested do not even log the requests containing only hello
  messages, which is appreciable.

  See also: "option httpchk"


option tcpka
  Enable or disable the sending of TCP keepalive packets on both sides
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments : none

  When there is a firewall or any session-aware component between a client and
  a server, and when the protocol involves very long sessions with long idle
  periods (eg: remote desktops), there is a risk that one of the intermediate
  components decides to expire a session which has remained idle for too long.

  Enabling socket-level TCP keep-alives makes the system regularly send packets
  to the other end of the connection, leaving it active. The delay between
  keep-alive probes is controlled by the system only and depends both on the
  operating system and its tuning parameters.

  It is important to understand that keep-alive packets are neither emitted nor
  received at the application level. It is only the network stacks which sees
  them. For this reason, even if one side of the proxy already uses keep-alives
  to maintain its connection alive, those keep-alive packets will not be
  forwarded to the other side of the proxy.

  Please note that this has nothing to do with HTTP keep-alive.

  Using option "tcpka" enables the emission of TCP keep-alive probes on both
  the client and server sides of a connection. Note that this is meaningful
  only in "defaults" or "listen" sections. If this option is used in a
  frontend, only the client side will get keep-alives, and if this option is
  used in a backend, only the server side will get keep-alives. For this
  reason, it is strongly recommended to explicitly use "option clitcpka" and
  "option srvtcpka" when the configuration is split between frontends and
  backends.

  See also : "option clitcpka", "option srvtcpka"


option tcplog
  Enable advanced logging of TCP connections with session state and timers
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments : none

  By default, the log output format is very poor, as it only contains the
  source and destination addresses, and the instance name. By specifying
  "option tcplog", each log line turns into a much richer format including, but
  not limited to, the connection timers, the session status, the connections
  numbers, the frontend, backend and server name, and of course the source
  address and ports. This option is useful for pure TCP proxies in order to
  find which of the client or server disconnects or times out. For normal HTTP
  proxies, it's better to use "option httplog" which is even more complete.

  This option may be set either in the frontend or the backend.

  See also :  "option httplog", and section 2.6 about logging.


option tcpsplice  [ experimental ]
  Enable linux kernel-based acceleration of data relaying
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments : none

  This option is only available when HAProxy has been built for use on Linux
  with USE_TCPSPLICE=1. This option requires a kernel patch which is available
  on http://www.linux-l7sw.org/.

  When "option tcpsplice" is set, as soon as the server's response headers have
  been transferred, the session handling is transferred to the kernel which
  will forward all subsequent data from the server to the client untill the
  session closes. This leads to much faster data transfers between client and
  server since the data is not copied twice between kernel and user space, but
  there are some limitations such as the lack of information about the number
  of bytes transferred and the total transfer time.

  This is an experimental feature. It happens to reliably work but issues
  caused by corner cases are to be expected.

  Note that this option requires that the process permanently runs with
  CAP_NETADMIN privileges, which most often translates into running as root.


option transparent
no option transparent
  Enable client-side transparent proxying
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments : none

  This option was introduced in order to provide layer 7 persistence to layer 3
  load balancers. The idea is to use the OS's ability to redirect an incoming
  connection for a remote address to a local process (here HAProxy), and let
  this process know what address was initially requested. When this option is
  used, sessions without cookies will be forwarded to the original destination
  IP address of the incoming request (which should match that of another
  equipment), while requests with cookies will still be forwarded to the
  appropriate server.

  Note that contrary to a common belief, this option does NOT make HAProxy
  present the client's IP to the server when establishing the connection.

  See also: the "usersrc" argument of the "source" keyword, and the
            "transparent" option of the "bind" keyword.


rate-limit sessions <rate>
  Set a limit on the number of new sessions accepted per second on a frontend
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   no
  Arguments :
    <rate>    The <rate> parameter is an integer designating the maximum number
              of new sessions per second to accept on the frontend.

  When the frontend reaches the specified number of new sessions per second, it
  stops accepting new connections until the rate drops below the limit again.
  During this time, the pending sessions will be kept in the socket's backlog
  (in system buffers) and haproxy will not even be aware that sessions are
  pending. When applying very low limit on a highly loaded service, it may make
  sense to increase the socket's backlog using the "backlog" keyword.

  This feature is particularly efficient at blocking connection-based attacks
  or service abuse on fragile servers. Since the session rate is measured every
  millisecond, it is extremely accurate. Also, the limit applies immediately,
  no delay is needed at all to detect the threshold.

  Example : limit the connection rate on SMTP to 10 per second max
        listen smtp
            mode tcp
            bind :25
            rate-limit sessions 10
            server 127.0.0.1:1025

  Note : when the maximum rate is reached, the frontend's status appears as
         "FULL" in the statistics, exactly as when it is saturated.

  See also : the "backlog" keyword and the "fe_sess_rate" ACL criterion.


redirect location <to> [code <code>] <option> {if | unless} <condition>
redirect prefix   <to> [code <code>] <option> {if | unless} <condition>
  Return an HTTP redirection if/unless a condition is matched
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    yes   |   yes  |   yes

  If/unless the condition is matched, the HTTP request will lead to a redirect
  response.

  Arguments :
    <to>      With "redirect location", the exact value in <to> is placed into
              the HTTP "Location" header. In case of "redirect prefix", the
              "Location" header is built from the concatenation of <to> and the
              complete URI, including the query string, unless the "drop-query"
              option is specified (see below). As a special case, if <to>
              equals exactly "/" in prefix mode, then nothing is inserted
              before the original URI. It allows one to redirect to the same
              URL.

    <code>    The code is optional. It indicates which type of HTTP redirection
              is desired. Only codes 301, 302 and 303 are supported, and 302 is
              used if no code is specified. 301 means "Moved permanently", and
              a browser may cache the Location. 302 means "Moved permanently"
              and means that the browser should not cache the redirection. 303
              is equivalent to 302 except that the browser will fetch the
              location with a GET method.

    <option>  There are several options which can be specified to adjust the
              expected behaviour of a redirection :

      - "drop-query"
        When this keyword is used in a prefix-based redirection, then the
        location will be set without any possible query-string, which is useful
        for directing users to a non-secure page for instance. It has no effect
        with a location-type redirect.

      - "set-cookie NAME[=value]"
        A "Set-Cookie" header will be added with NAME (and optionally "=value")
        to the response. This is sometimes used to indicate that a user has
        been seen, for instance to protect against some types of DoS. No other
        cookie option is added, so the cookie will be a session cookie. Note
        that for a browser, a sole cookie name without an equal sign is
        different from a cookie with an equal sign.

      - "clear-cookie NAME[=]"
        A "Set-Cookie" header will be added with NAME (and optionally "="), but
        with the "Max-Age" attribute set to zero. This will tell the browser to
        delete this cookie. It is useful for instance on logout pages. It is
        important to note that clearing the cookie "NAME" will not remove a
        cookie set with "NAME=value". You have to clear the cookie "NAME=" for
        that, because the browser makes the difference.

  Example: move the login URL only to HTTPS.
        acl clear      dst_port  80
        acl secure     dst_port  8080
        acl login_page url_beg   /login
        acl logout     url_beg   /logout
        acl uid_given  url_reg   /login?userid=[^&]+
        acl cookie_set hdr_sub(cookie) SEEN=1

        redirect prefix   https://mysite.com set-cookie SEEN=1 if !cookie_set
        redirect prefix   https://mysite.com           if login_page !secure
        redirect prefix   http://mysite.com drop-query if login_page !uid_given
        redirect location http://mysite.com/           if !login_page secure
        redirect location / clear-cookie USERID=       if logout

  See section 2.3 about ACL usage.


redisp (deprecated)
redispatch (deprecated)
  Enable or disable session redistribution in case of connection failure
  May be used in sections:    defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments : none

  In HTTP mode, if a server designated by a cookie is down, clients may
  definitely stick to it because they cannot flush the cookie, so they will not
  be able to access the service anymore.

  Specifying "redispatch" will allow the proxy to break their persistence and
  redistribute them to a working server.

  It also allows to retry last connection to another server in case of multiple
  connection failures. Of course, it requires having "retries" set to a nonzero
  value.
  
  This form is deprecated, do not use it in any new configuration, use the new
  "option redispatch" instead.

  See also : "option redispatch"


reqadd  <string>
  Add a header at the end of the HTTP request
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    yes   |   yes  |   yes
  Arguments :
    <string>  is the complete line to be added. Any space or known delimiter
              must be escaped using a backslash ('\'). Please refer to section
              2.5 about HTTP header manipulation for more information.

  A new line consisting in <string> followed by a line feed will be added after
  the last header of an HTTP request.

  Header transformations only apply to traffic which passes through HAProxy,
  and not to traffic generated by HAProxy, such as health-checks or error
  responses.

  See also: "rspadd" and section 2.5 about HTTP header manipulation


reqallow  <search>
reqiallow <search>  (ignore case)
  Definitely allow an HTTP request if a line matches a regular expression
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    yes   |   yes  |   yes
  Arguments :
    <search>  is the regular expression applied to HTTP headers and to the
              request line. This is an extended regular expression. Parenthesis
              grouping is supported and no preliminary backslash is required.
              Any space or known delimiter must be escaped using a backslash
              ('\'). The pattern applies to a full line at a time. The
              "reqallow" keyword strictly matches case while "reqiallow"
              ignores case.

  A request containing any line which matches extended regular expression
  <search> will mark the request as allowed, even if any later test would
  result in a deny. The test applies both to the request line and to request
  headers. Keep in mind that URLs in request line are case-sensitive while
  header names are not. 

  It is easier, faster and more powerful to use ACLs to write access policies.
  Reqdeny, reqallow and reqpass should be avoided in new designs.

  Example :
     # allow www.* but refuse *.local
     reqiallow ^Host:\ www\.
     reqideny  ^Host:\ .*\.local

  See also: "reqdeny", "acl", "block" and section 2.5 about HTTP header
            manipulation


reqdel  <search>
reqidel <search>  (ignore case)
  Delete all headers matching a regular expression in an HTTP request
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    yes   |   yes  |   yes
  Arguments :
    <search>  is the regular expression applied to HTTP headers and to the
              request line. This is an extended regular expression. Parenthesis
              grouping is supported and no preliminary backslash is required.
              Any space or known delimiter must be escaped using a backslash
              ('\'). The pattern applies to a full line at a time. The "reqdel"
              keyword strictly matches case while "reqidel" ignores case.

  Any header line matching extended regular expression <search> in the request
  will be completely deleted. Most common use of this is to remove unwanted
  and/or dangerous headers or cookies from a request before passing it to the
  next servers.

  Header transformations only apply to traffic which passes through HAProxy,
  and not to traffic generated by HAProxy, such as health-checks or error
  responses. Keep in mind that header names are not case-sensitive.

  Example :
     # remove X-Forwarded-For header and SERVER cookie
     reqidel ^X-Forwarded-For:.*
     reqidel ^Cookie:.*SERVER=

  See also: "reqadd", "reqrep", "rspdel" and section 2.5 about HTTP header
            manipulation


reqdeny  <search>
reqideny <search>  (ignore case)
  Deny an HTTP request if a line matches a regular expression
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    yes   |   yes  |   yes
  Arguments :
    <search>  is the regular expression applied to HTTP headers and to the
              request line. This is an extended regular expression. Parenthesis
              grouping is supported and no preliminary backslash is required.
              Any space or known delimiter must be escaped using a backslash
              ('\'). The pattern applies to a full line at a time. The
              "reqdeny" keyword strictly matches case while "reqideny" ignores
              case.

  A request containing any line which matches extended regular expression
  <search> will mark the request as denied, even if any later test would
  result in an allow. The test applies both to the request line and to request
  headers. Keep in mind that URLs in request line are case-sensitive while
  header names are not. 

  A denied request will generate an "HTTP 403 forbidden" response once the
  complete request has been parsed. This is consistent with what is practiced
  using ACLs. 

  It is easier, faster and more powerful to use ACLs to write access policies.
  Reqdeny, reqallow and reqpass should be avoided in new designs.

  Example :
     # refuse *.local, then allow www.*
     reqideny  ^Host:\ .*\.local
     reqiallow ^Host:\ www\.

  See also: "reqallow", "rspdeny", "acl", "block" and section 2.5 about HTTP
            header manipulation


reqpass  <search>
reqipass <search>  (ignore case)
  Ignore any HTTP request line matching a regular expression in next rules
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    yes   |   yes  |   yes
  Arguments :
    <search>  is the regular expression applied to HTTP headers and to the
              request line. This is an extended regular expression. Parenthesis
              grouping is supported and no preliminary backslash is required.
              Any space or known delimiter must be escaped using a backslash
              ('\'). The pattern applies to a full line at a time. The
              "reqpass" keyword strictly matches case while "reqipass" ignores
              case.

  A request containing any line which matches extended regular expression
  <search> will skip next rules, without assigning any deny or allow verdict.
  The test applies both to the request line and to request headers. Keep in
  mind that URLs in request line are case-sensitive while header names are not.

  It is easier, faster and more powerful to use ACLs to write access policies.
  Reqdeny, reqallow and reqpass should be avoided in new designs.

  Example :
     # refuse *.local, then allow www.*, but ignore "www.private.local"
     reqipass  ^Host:\ www.private\.local
     reqideny  ^Host:\ .*\.local
     reqiallow ^Host:\ www\.

  See also: "reqallow", "reqdeny", "acl", "block" and section 2.5 about HTTP
            header manipulation


reqrep  <search> <string>
reqirep <search> <string>   (ignore case)
  Replace a regular expression with a string in an HTTP request line
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    yes   |   yes  |   yes
  Arguments :
    <search>  is the regular expression applied to HTTP headers and to the
              request line. This is an extended regular expression. Parenthesis
              grouping is supported and no preliminary backslash is required.
              Any space or known delimiter must be escaped using a backslash
              ('\'). The pattern applies to a full line at a time. The "reqrep"
              keyword strictly matches case while "reqirep" ignores case.

    <string>  is the complete line to be added. Any space or known delimiter
              must be escaped using a backslash ('\'). References to matched
              pattern groups are possible using the common \N form, with N
              being a single digit between 0 and 9. Please refer to section
              2.5 about HTTP header manipulation for more information.

  Any line matching extended regular expression <search> in the request (both
  the request line and header lines) will be completely replaced with <string>.
  Most common use of this is to rewrite URLs or domain names in "Host" headers.

  Header transformations only apply to traffic which passes through HAProxy,
  and not to traffic generated by HAProxy, such as health-checks or error
  responses. Note that for increased readability, it is suggested to add enough
  spaces between the request and the response. Keep in mind that URLs in
  request line are case-sensitive while header names are not.

  Example :
     # replace "/static/" with "/" at the beginning of any request path.
     reqrep ^([^\ ]*)\ /static/(.*)     \1\ /\2
     # replace "www.mydomain.com" with "www" in the host name.
     reqirep ^Host:\ www.mydomain.com   Host:\ www

  See also: "reqadd", "reqdel", "rsprep" and section 2.5 about HTTP header
            manipulation


reqtarpit  <search>
reqitarpit <search>  (ignore case)
  Tarpit an HTTP request containing a line matching a regular expression
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    yes   |   yes  |   yes
  Arguments :
    <search>  is the regular expression applied to HTTP headers and to the
              request line. This is an extended regular expression. Parenthesis
              grouping is supported and no preliminary backslash is required.
              Any space or known delimiter must be escaped using a backslash
              ('\'). The pattern applies to a full line at a time. The
              "reqtarpit" keyword strictly matches case while "reqitarpit"
              ignores case.

  A request containing any line which matches extended regular expression
  <search> will be tarpitted, which means that it will connect to nowhere, will
  be kept open for a pre-defined time, then will return an HTTP error 500 so
  that the attacker does not suspect it has been tarpitted. The status 500 will
  be reported in the logs, but the completion flags will indicate "PT". The
  delay is defined by "timeout tarpit", or "timeout connect" if the former is
  not set.

  The goal of the tarpit is to slow down robots attacking servers with
  identifiable requests. Many robots limit their outgoing number of connections
  and stay connected waiting for a reply which can take several minutes to
  come. Depending on the environment and attack, it may be particularly
  efficient at reducing the load on the network and firewalls.

  Example :
     # ignore user-agents reporting any flavour of "Mozilla" or "MSIE", but
     # block all others.
     reqipass   ^User-Agent:\.*(Mozilla|MSIE)
     reqitarpit ^User-Agent:

  See also: "reqallow", "reqdeny", "reqpass", and section 2.5 about HTTP header
            manipulation


retries <value>
  Set the number of retries to perform on a server after a connection failure
  May be used in sections:    defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments :
    <value>   is the number of times a connection attempt should be retried on
              a server when a connection either is refused or times out. The
              default value is 3.

  It is important to understand that this value applies to the number of
  connection attempts, not full requests. When a connection has effectively
  been established to a server, there will be no more retry.

  In order to avoid immediate reconnections to a server which is restarting,
  a turn-around timer of 1 second is applied before a retry occurs.

  When "option redispatch" is set, the last retry may be performed on another
  server even if a cookie references a different server.

  See also : "option redispatch"


rspadd <string>
  Add a header at the end of the HTTP response
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    yes   |   yes  |   yes
  Arguments :
    <string>  is the complete line to be added. Any space or known delimiter
              must be escaped using a backslash ('\'). Please refer to section
              2.5 about HTTP header manipulation for more information.

  A new line consisting in <string> followed by a line feed will be added after
  the last header of an HTTP response.

  Header transformations only apply to traffic which passes through HAProxy,
  and not to traffic generated by HAProxy, such as health-checks or error
  responses.

  See also: "reqadd" and section 2.5 about HTTP header manipulation


rspdel  <search>
rspidel <search>  (ignore case)
  Delete all headers matching a regular expression in an HTTP response
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    yes   |   yes  |   yes
  Arguments :
    <search>  is the regular expression applied to HTTP headers and to the
              response line. This is an extended regular expression, so
              parenthesis grouping is supported and no preliminary backslash
              is required. Any space or known delimiter must be escaped using
              a backslash ('\'). The pattern applies to a full line at a time.
              The "rspdel" keyword strictly matches case while "rspidel"
              ignores case.

  Any header line matching extended regular expression <search> in the response
  will be completely deleted. Most common use of this is to remove unwanted
  and/or sensible headers or cookies from a response before passing it to the
  client.

  Header transformations only apply to traffic which passes through HAProxy,
  and not to traffic generated by HAProxy, such as health-checks or error
  responses. Keep in mind that header names are not case-sensitive.

  Example :
     # remove the Server header from responses
     reqidel ^Server:.*

  See also: "rspadd", "rsprep", "reqdel" and section 2.5 about HTTP header
            manipulation


rspdeny  <search>
rspideny <search>  (ignore case)
  Block an HTTP response if a line matches a regular expression
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    yes   |   yes  |   yes
  Arguments :
    <search>  is the regular expression applied to HTTP headers and to the
              response line. This is an extended regular expression, so
              parenthesis grouping is supported and no preliminary backslash
              is required. Any space or known delimiter must be escaped using
              a backslash ('\'). The pattern applies to a full line at a time.
              The "rspdeny" keyword strictly matches case while "rspideny"
              ignores case.

  A response containing any line which matches extended regular expression
  <search> will mark the request as denied. The test applies both to the
  response line and to response headers. Keep in mind that header names are not
  case-sensitive.

  Main use of this keyword is to prevent sensitive information leak and to
  block the response before it reaches the client. If a response is denied, it
  will be replaced with an HTTP 502 error so that the client never retrieves
  any sensitive data.

  It is easier, faster and more powerful to use ACLs to write access policies.
  Rspdeny should be avoided in new designs.

  Example :
     # Ensure that no content type matching ms-word will leak
     rspideny  ^Content-type:\.*/ms-word

  See also: "reqdeny", "acl", "block" and section 2.5 about HTTP header
            manipulation


rsprep  <search> <string>
rspirep <search> <string>  (ignore case)
  Replace a regular expression with a string in an HTTP response line
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    yes   |   yes  |   yes
  Arguments :
    <search>  is the regular expression applied to HTTP headers and to the
              response line. This is an extended regular expression, so
              parenthesis grouping is supported and no preliminary backslash
              is required. Any space or known delimiter must be escaped using
              a backslash ('\'). The pattern applies to a full line at a time.
              The "rsprep" keyword strictly matches case while "rspirep"
              ignores case.

    <string>  is the complete line to be added. Any space or known delimiter
              must be escaped using a backslash ('\'). References to matched
              pattern groups are possible using the common \N form, with N
              being a single digit between 0 and 9. Please refer to section
              2.5 about HTTP header manipulation for more information.

  Any line matching extended regular expression <search> in the response (both
  the response line and header lines) will be completely replaced with
  <string>. Most common use of this is to rewrite Location headers.

  Header transformations only apply to traffic which passes through HAProxy,
  and not to traffic generated by HAProxy, such as health-checks or error
  responses. Note that for increased readability, it is suggested to add enough
  spaces between the request and the response. Keep in mind that header names
  are not case-sensitive.

  Example :
     # replace "Location: 127.0.0.1:8080" with "Location: www.mydomain.com"
     rspirep ^Location:\ 127.0.0.1:8080    Location:\ www.mydomain.com

  See also: "rspadd", "rspdel", "reqrep" and section 2.5 about HTTP header
            manipulation


server <name> <address>[:port] [param*]
  Declare a server in a backend
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    no    |   yes  |   yes
  Arguments :
    <name>    is the internal name assigned to this server. This name will
              appear in logs and alerts.

    <address> is the IPv4 address of the server. Alternatively, a resolvable
              hostname is supported, but this name will be resolved during
              start-up.

    <ports>   is an optional port specification. If set, all connections will
              be sent to this port. If unset, the same port the client
              connected to will be used. The port may also be prefixed by a "+"
              or a "-". In this case, the server's port will be determined by
              adding this value to the client's port.

    <param*>  is a list of parameters for this server. The "server" keywords
              accepts an important number of options and has a complete section
              dedicated to it. Please refer to section 2.4 for more details.

  Examples :
        server first  10.1.1.1:1080 cookie first  check inter 1000
        server second 10.1.1.2:1080 cookie second check inter 1000

  See also : section 2.4 about server options


source <addr>[:<port>] [usesrc { <addr2>[:<port2>] | client | clientip } ]
source <addr>[:<port>] [interface <name>]
  Set the source address for outgoing connections
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments :
    <addr>    is the IPv4 address HAProxy will bind to before connecting to a
              server. This address is also used as a source for health checks.
              The default value of 0.0.0.0 means that the system will select
              the most appropriate address to reach its destination.

    <port>    is an optional port. It is normally not needed but may be useful
              in some very specific contexts. The default value of zero means
              the system will select a free port.

    <addr2>   is the IP address to present to the server when connections are
              forwarded in full transparent proxy mode. This is currently only
              supported on some patched Linux kernels. When this address is
              specified, clients connecting to the server will be presented
              with this address, while health checks will still use the address
              <addr>.

    <port2>   is the optional port to present to the server when connections
              are forwarded in full transparent proxy mode (see <addr2> above).
              The default value of zero means the system will select a free
              port.

    <name>    is an optional interface name to which to bind to for outgoing
              traffic. On systems supporting this features (currently, only
              Linux), this allows one to bind all traffic to the server to
              this interface even if it is not the one the system would select
              based on routing tables. This should be used with extreme care.
              Note that using this option requires root privileges.

  The "source" keyword is useful in complex environments where a specific
  address only is allowed to connect to the servers. It may be needed when a
  private address must be used through a public gateway for instance, and it is
  known that the system cannot determine the adequate source address by itself.

  An extension which is available on certain patched Linux kernels may be used
  through the "usesrc" optional keyword. It makes it possible to connect to the
  servers with an IP address which does not belong to the system itself. This
  is called "full transparent proxy mode". For this to work, the destination
  servers have to route their traffic back to this address through the machine
  running HAProxy, and IP forwarding must generally be enabled on this machine.

  In this "full transparent proxy" mode, it is possible to force a specific IP
  address to be presented to the servers. This is not much used in fact. A more
  common use is to tell HAProxy to present the client's IP address. For this,
  there are two methods :

    - present the client's IP and port addresses. This is the most transparent
      mode, but it can cause problems when IP connection tracking is enabled on
      the machine, because a same connection may be seen twice with different
      states. However, this solution presents the huge advantage of not
      limiting the system to the 64k outgoing address+port couples, because all
      of the client ranges may be used.

    - present only the client's IP address and select a spare port. This
      solution is still quite elegant but slightly less transparent (downstream
      firewalls logs will not match upstream's). It also presents the downside
      of limiting the number of concurrent connections to the usual 64k ports.
      However, since the upstream and downstream ports are different, local IP
      connection tracking on the machine will not be upset by the reuse of the
      same session.

  Note that depending on the transparent proxy technology used, it may be
  required to force the source address. In fact, cttproxy version 2 requires an
  IP address in <addr> above, and does not support setting of "0.0.0.0" as the
  IP address because it creates NAT entries which much match the exact outgoing
  address. Tproxy version 4 and some other kernel patches which work in pure
  forwarding mode generally will not have this limitation.

  This option sets the default source for all servers in the backend. It may
  also be specified in a "defaults" section. Finer source address specification
  is possible at the server level using the "source" server option. Refer to
  section 2.4 for more information.

  Examples :
        backend private
            # Connect to the servers using our 192.168.1.200 source address
            source 192.168.1.200

        backend transparent_ssl1
            # Connect to the SSL farm from the client's source address
            source 192.168.1.200 usesrc clientip

        backend transparent_ssl2
            # Connect to the SSL farm from the client's source address and port
            # not recommended if IP conntrack is present on the local machine.
            source 192.168.1.200 usesrc client

        backend transparent_ssl3
            # Connect to the SSL farm from the client's source address. It
            # is more conntrack-friendly.
            source 192.168.1.200 usesrc clientip

        backend transparent_smtp
            # Connect to the SMTP farm from the client's source address/port
            # with Tproxy version 4.
            source 0.0.0.0 usesrc clientip

  See also : the "source" server option in section 2.4, the Tproxy patches for
             the Linux kernel on www.balabit.com, the "bind" keyword.


srvtimeout <timeout> (deprecated)
  Set the maximum inactivity time on the server side.
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments :
    <timeout> is the timeout value specified in milliseconds by default, but
              can be in any other unit if the number is suffixed by the unit,
              as explained at the top of this document.

  The inactivity timeout applies when the server is expected to acknowledge or
  send data. In HTTP mode, this timeout is particularly important to consider
  during the first phase of the server's response, when it has to send the
  headers, as it directly represents the server's processing time for the
  request. To find out what value to put there, it's often good to start with
  what would be considered as unacceptable response times, then check the logs
  to observe the response time distribution, and adjust the value accordingly.

  The value is specified in milliseconds by default, but can be in any other
  unit if the number is suffixed by the unit, as specified at the top of this
  document. In TCP mode (and to a lesser extent, in HTTP mode), it is highly
  recommended that the client timeout remains equal to the server timeout in
  order to avoid complex situations to debug. Whatever the expected server
  response times, it is a good practice to cover at least one or several TCP
  packet losses by specifying timeouts that are slightly above multiples of 3
  seconds (eg: 4 or 5 seconds minimum). 

  This parameter is specific to backends, but can be specified once for all in
  "defaults" sections. This is in fact one of the easiest solutions not to
  forget about it. An unspecified timeout results in an infinite timeout, which
  is not recommended. Such a usage is accepted and works but reports a warning
  during startup because it may results in accumulation of expired sessions in
  the system if the system's timeouts are not configured either.

  This parameter is provided for compatibility but is currently deprecated.
  Please use "timeout server" instead.

  See also : "timeout server", "timeout client" and "clitimeout".


stats auth <user>:<passwd>
  Enable statistics with authentication and grant access to an account
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments :
    <user>    is a user name to grant access to

    <passwd>  is the cleartext password associated to this user

  This statement enables statistics with default settings, and restricts access
  to declared users only. It may be repeated as many times as necessary to
  allow as many users as desired. When a user tries to access the statistics
  without a valid account, a "401 Forbidden" response will be returned so that
  the browser asks the user to provide a valid user and password. The real
  which will be returned to the browser is configurable using "stats realm".

  Since the authentication method is HTTP Basic Authentication, the passwords
  circulate in cleartext on the network. Thus, it was decided that the
  configuration file would also use cleartext passwords to remind the users
  that those ones should not be sensible and not shared with any other account.

  It is also possible to reduce the scope of the proxies which appear in the
  report using "stats scope".

  Though this statement alone is enough to enable statistics reporting, it is
  recommended to set all other settings in order to avoid relying on default
  unobvious parameters.

  Example :
    # public access (limited to this backend only)
    backend public_www
        server srv1 192.168.0.1:80
        stats enable
        stats hide-version
        stats scope   .
        stats uri     /admin?stats
        stats realm   Haproxy\ Statistics
        stats auth    admin1:AdMiN123
        stats auth    admin2:AdMiN321

    # internal monitoring access (unlimited)
    backend private_monitoring
        stats enable
        stats uri     /admin?stats
        stats refresh 5s

  See also : "stats enable", "stats realm", "stats scope", "stats uri"


stats enable
  Enable statistics reporting with default settings
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments : none

  This statement enables statistics reporting with default settings defined
  at build time. Unless stated otherwise, these settings are used :
    - stats uri   : /haproxy?stats
    - stats realm : "HAProxy Statistics"
    - stats auth  : no authentication
    - stats scope : no restriction

  Though this statement alone is enough to enable statistics reporting, it is
  recommended to set all other settings in order to avoid relying on default
  unobvious parameters.

  Example :
    # public access (limited to this backend only)
    backend public_www
        server srv1 192.168.0.1:80
        stats enable
        stats hide-version
        stats scope   .
        stats uri     /admin?stats
        stats realm   Haproxy\ Statistics
        stats auth    admin1:AdMiN123
        stats auth    admin2:AdMiN321

    # internal monitoring access (unlimited)
    backend private_monitoring
        stats enable
        stats uri     /admin?stats
        stats refresh 5s

  See also : "stats auth", "stats realm", "stats uri"


stats realm <realm>
  Enable statistics and set authentication realm
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments :
    <realm>   is the name of the HTTP Basic Authentication realm reported to
              the browser. The browser uses it to display it in the pop-up
              inviting the user to enter a valid username and password.

  The realm is read as a single word, so any spaces in it should be escaped
  using a backslash ('\').

  This statement is useful only in conjunction with "stats auth" since it is
  only related to authentication.

  Though this statement alone is enough to enable statistics reporting, it is
  recommended to set all other settings in order to avoid relying on default
  unobvious parameters.

  Example :
    # public access (limited to this backend only)
    backend public_www
        server srv1 192.168.0.1:80
        stats enable
        stats hide-version
        stats scope   .
        stats uri     /admin?stats
        stats realm   Haproxy\ Statistics
        stats auth    admin1:AdMiN123
        stats auth    admin2:AdMiN321

    # internal monitoring access (unlimited)
    backend private_monitoring
        stats enable
        stats uri     /admin?stats
        stats refresh 5s

  See also : "stats auth", "stats enable", "stats uri"


stats refresh <delay>
  Enable statistics with automatic refresh
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments :
    <delay>   is the suggested refresh delay, specified in seconds, which will
              be returned to the browser consulting the report page. While the
              browser is free to apply any delay, it will generally respect it
              and refresh the page this every seconds. The refresh interval may
              be specified in any other non-default time unit, by suffixing the
              unit after the value, as explained at the top of this document.

  This statement is useful on monitoring displays with a permanent page
  reporting the load balancer's activity. When set, the HTML report page will
  include a link "refresh"/"stop refresh" so that the user can select whether
  he wants automatic refresh of the page or not.

  Though this statement alone is enough to enable statistics reporting, it is
  recommended to set all other settings in order to avoid relying on default
  unobvious parameters.

  Example :
    # public access (limited to this backend only)
    backend public_www
        server srv1 192.168.0.1:80
        stats enable
        stats hide-version
        stats scope   .
        stats uri     /admin?stats
        stats realm   Haproxy\ Statistics
        stats auth    admin1:AdMiN123
        stats auth    admin2:AdMiN321

    # internal monitoring access (unlimited)
    backend private_monitoring
        stats enable
        stats uri     /admin?stats
        stats refresh 5s

  See also : "stats auth", "stats enable", "stats realm", "stats uri"


stats scope { <name> | "." }
  Enable statistics and limit access scope
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments :
    <name>    is the name of a listen, frontend or backend section to be
              reported. The special name "." (a single dot) designates the
              section in which the statement appears.

  When this statement is specified, only the sections enumerated with this
  statement will appear in the report. All other ones will be hidden. This
  statement may appear as many times as needed if multiple sections need to be
  reported. Please note that the name checking is performed as simple string
  comparisons, and that it is never checked that a give section name really
  exists.

  Though this statement alone is enough to enable statistics reporting, it is
  recommended to set all other settings in order to avoid relying on default
  unobvious parameters.

  Example :
    # public access (limited to this backend only)
    backend public_www
        server srv1 192.168.0.1:80
        stats enable
        stats hide-version
        stats scope   .
        stats uri     /admin?stats
        stats realm   Haproxy\ Statistics
        stats auth    admin1:AdMiN123
        stats auth    admin2:AdMiN321

    # internal monitoring access (unlimited)
    backend private_monitoring
        stats enable
        stats uri     /admin?stats
        stats refresh 5s

  See also : "stats auth", "stats enable", "stats realm", "stats uri"


stats uri <prefix>
  Enable statistics and define the URI prefix to access them
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments :
    <prefix>  is the prefix of any URI which will be redirected to stats. This
              prefix may contain a question mark ('?') to indicate part of a
              query string.

  The statistics URI is intercepted on the relayed traffic, so it appears as a
  page within the normal application. It is strongly advised to ensure that the
  selected URI will never appear in the application, otherwise it will never be
  possible to reach it in the application.

  The default URI compiled in haproxy is "/haproxy?stats", but this may be
  changed at build time, so it's better to always explictly specify it here.
  It is generally a good idea to include a question mark in the URI so that
  intermediate proxies refrain from caching the results. Also, since any string
  beginning with the prefix will be accepted as a stats request, the question
  mark helps ensuring that no valid URI will begin with the same words.

  It is sometimes very convenient to use "/" as the URI prefix, and put that
  statement in a "listen" instance of its own. That makes it easy to dedicate
  an address or a port to statistics only.

  Though this statement alone is enough to enable statistics reporting, it is
  recommended to set all other settings in order to avoid relying on default
  unobvious parameters.

  Example :
    # public access (limited to this backend only)
    backend public_www
        server srv1 192.168.0.1:80
        stats enable
        stats hide-version
        stats scope   .
        stats uri     /admin?stats
        stats realm   Haproxy\ Statistics
        stats auth    admin1:AdMiN123
        stats auth    admin2:AdMiN321

    # internal monitoring access (unlimited)
    backend private_monitoring
        stats enable
        stats uri     /admin?stats
        stats refresh 5s

  See also : "stats auth", "stats enable", "stats realm"


stats hide-version
  Enable statistics and hide HAProxy version reporting
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments : none

  By default, the stats page reports some useful status information along with
  the statistics. Among them is HAProxy's version. However, it is generally
  considered dangerous to report precise version to anyone, as it can help them
  target known weaknesses with specific attacks. The "stats hide-version"
  statement removes the version from the statistics report. This is recommended
  for public sites or any site with a weak login/password.

  Though this statement alone is enough to enable statistics reporting, it is
  recommended to set all other settings in order to avoid relying on default
  unobvious parameters.

  Example :
    # public access (limited to this backend only)
    backend public_www
        server srv1 192.168.0.1:80
        stats enable
        stats hide-version
        stats scope   .
        stats uri     /admin?stats
        stats realm   Haproxy\ Statistics
        stats auth    admin1:AdMiN123
        stats auth    admin2:AdMiN321

    # internal monitoring access (unlimited)
    backend private_monitoring
        stats enable
        stats uri     /admin?stats
        stats refresh 5s

  See also : "stats auth", "stats enable", "stats realm", "stats uri"


tcp-request content accept [{if | unless} <condition>]
  Accept a connection if/unless a content inspection condition is matched
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    yes   |   yes  |   no

  During TCP content inspection, the connection is immediately validated if the
  condition is true (when used with "if") or false (when used with "unless").
  Most of the time during content inspection, a condition will be in an
  uncertain state which is neither true nor false. The evaluation immediately
  stops when such a condition is encountered. It is important to understand
  that "accept" and "reject" rules are evaluated in their exact declaration
  order, so that it is possible to build complex rules from them. There is no
  specific limit to the number of rules which may be inserted.

  Note that the "if/unless" condition is optionnal. If no condition is set on
  the action, it is simply performed unconditionally.

  If no "tcp-request content" rules are matched, the default action already is
  "accept". Thus, this statement alone does not bring anything without another
  "reject" statement.

  See section 2.3 about ACL usage.

  See also : "tcp-request content-reject", "tcp-request inspect-delay"


tcp-request content reject [{if | unless} <condition>]
  Reject a connection if/unless a content inspection condition is matched
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    yes   |   yes  |   no

  During TCP content inspection, the connection is immediately rejected if the
  condition is true (when used with "if") or false (when used with "unless").
  Most of the time during content inspection, a condition will be in an
  uncertain state which is neither true nor false. The evaluation immediately
  stops when such a condition is encountered. It is important to understand
  that "accept" and "reject" rules are evaluated in their exact declaration
  order, so that it is possible to build complex rules from them. There is no
  specific limit to the number of rules which may be inserted.

  Note that the "if/unless" condition is optionnal. If no condition is set on
  the action, it is simply performed unconditionally.

  If no "tcp-request content" rules are matched, the default action is set to
  "accept".

  Example:
        # reject SMTP connection if client speaks first
        tcp-request inspect-delay 30s
        acl content_present req_len gt 0
        tcp-request reject if content_present

        # Forward HTTPS connection only if client speaks
        tcp-request inspect-delay 30s
        acl content_present req_len gt 0
        tcp-request accept if content_present
        tcp-request reject

  See section 2.3 about ACL usage.

  See also : "tcp-request content-accept", "tcp-request inspect-delay"


tcp-request inspect-delay <timeout>
  Set the maximum allowed time to wait for data during content inspection
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    yes   |   yes  |   no
  Arguments :
    <timeout> is the timeout value specified in milliseconds by default, but
              can be in any other unit if the number is suffixed by the unit,
              as explained at the top of this document.

  People using haproxy primarily as a TCP relay are often worried about the
  risk of passing any type of protocol to a server without any analysis. In
  order to be able to analyze the request contents, we must first withhold
  the data then analyze them. This statement simply enables withholding of
  data for at most the specified amount of time.

  Note that when performing content inspection, haproxy will evaluate the whole
  rules for every new chunk which gets in, taking into account the fact that
  those data are partial. If no rule matches before the aforementionned delay,
  a last check is performed upon expiration, this time considering that the
  contents are definitive. If no delay is set, haproxy will not wait at all
  and will immediately apply a verdict based on the available information.
  Obviously this is unlikely to be very useful and might even be racy, so such
  setups are not recommended.

  As soon as a rule matches, the request is released and continues as usual. If
  the timeout is reached and no rule matches, the default policy will be to let
  it pass through unaffected.

  For most protocols, it is enough to set it to a few seconds, as most clients
  send the full request immediately upon connection. Add 3 or more seconds to
  cover TCP retransmits but that's all. For some protocols, it may make sense
  to use large values, for instance to ensure that the client never talks 
  before the server (eg: SMTP), or to wait for a client to talk before passing
  data to the server (eg: SSL). Note that the client timeout must cover at
  least the inspection delay, otherwise it will expire first.

  See also : "tcp-request content accept", "tcp-request content-reject",
             "timeout client".


timeout check <timeout>
  Set additional check timeout, but only after a connection has been already
  established.

  May be used in sections:    defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments:
    <timeout> is the timeout value specified in milliseconds by default, but
              can be in any other unit if the number is suffixed by the unit,
              as explained at the top of this document.

  If set, haproxy uses min("timeout connect", "inter") as a connect timeout
  for check and "timeout check" as an additional read timeout. The "min" is
  used so that people running with *very* long "timeout connect" (eg. those
  who needed this due to the queue or tarpit) do not slow down their checks.
  Of course it is better to use "check queue" and "check tarpit" instead of
  long "timeout connect".

  If "timeout check" is not set haproxy uses "inter" for complete check
  timeout (connect + read) exactly like all <1.3.15 version.

  In most cases check request is much simpler and faster to handle than normal
  requests and people may want to kick out laggy servers so this timeout should
  be smaller than "timeout server".

  This parameter is specific to backends, but can be specified once for all in
  "defaults" sections. This is in fact one of the easiest solutions not to
  forget about it.

  See also: "timeout connect", "timeout queue", "timeout server",
            "timeout tarpit".


timeout client <timeout>
timeout clitimeout <timeout> (deprecated)
  Set the maximum inactivity time on the client side.
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   no
  Arguments :
    <timeout> is the timeout value specified in milliseconds by default, but
              can be in any other unit if the number is suffixed by the unit,
              as explained at the top of this document.

  The inactivity timeout applies when the client is expected to acknowledge or
  send data. In HTTP mode, this timeout is particularly important to consider
  during the first phase, when the client sends the request, and during the
  response while it is reading data sent by the server. The value is specified
  in milliseconds by default, but can be in any other unit if the number is
  suffixed by the unit, as specified at the top of this document. In TCP mode
  (and to a lesser extent, in HTTP mode), it is highly recommended that the
  client timeout remains equal to the server timeout in order to avoid complex
  situations to debug. It is a good practice to cover one or several TCP packet
  losses by specifying timeouts that are slightly above multiples of 3 seconds
  (eg: 4 or 5 seconds).

  This parameter is specific to frontends, but can be specified once for all in
  "defaults" sections. This is in fact one of the easiest solutions not to
  forget about it. An unspecified timeout results in an infinite timeout, which
  is not recommended. Such a usage is accepted and works but reports a warning
  during startup because it may results in accumulation of expired sessions in
  the system if the system's timeouts are not configured either.

  This parameter replaces the old, deprecated "clitimeout". It is recommended
  to use it to write new configurations. The form "timeout clitimeout" is
  provided only by backwards compatibility but its use is strongly discouraged.

  See also : "clitimeout", "timeout server".


timeout connect <timeout>
timeout contimeout <timeout> (deprecated)
  Set the maximum time to wait for a connection attempt to a server to succeed.
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments :
    <timeout> is the timeout value specified in milliseconds by default, but
              can be in any other unit if the number is suffixed by the unit,
              as explained at the top of this document.

  If the server is located on the same LAN as haproxy, the connection should be
  immediate (less than a few milliseconds). Anyway, it is a good practice to
  cover one or several TCP packet losses by specifying timeouts that are 
  slightly above multiples of 3 seconds (eg: 4 or 5 seconds). By default, the
  connect timeout also presets both queue and tarpit timeouts to the same value
  if these have not been specified.

  This parameter is specific to backends, but can be specified once for all in
  "defaults" sections. This is in fact one of the easiest solutions not to
  forget about it. An unspecified timeout results in an infinite timeout, which
  is not recommended. Such a usage is accepted and works but reports a warning
  during startup because it may results in accumulation of failed sessions in
  the system if the system's timeouts are not configured either.

  This parameter replaces the old, deprecated "contimeout". It is recommended
  to use it to write new configurations. The form "timeout contimeout" is
  provided only by backwards compatibility but its use is strongly discouraged.

  See also: "timeout check", "timeout queue", "timeout server", "contimeout",
            "timeout tarpit".


timeout http-request <timeout>
  Set the maximum allowed time to wait for a complete HTTP request
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   no
  Arguments :
    <timeout> is the timeout value specified in milliseconds by default, but
              can be in any other unit if the number is suffixed by the unit,
              as explained at the top of this document.

  In order to offer DoS protection, it may be required to lower the maximum
  accepted time to receive a complete HTTP request without affecting the client
  timeout. This helps protecting against established connections on which
  nothing is sent. The client timeout cannot offer a good protection against
  this abuse because it is an inactivity timeout, which means that if the
  attacker sends one character every now and then, the timeout will not
  trigger. With the HTTP request timeout, no matter what speed the client
  types, the request will be aborted if it does not complete in time.

  Note that this timeout only applies to the header part of the request, and
  not to any data. As soon as the empty line is received, this timeout is not
  used anymore.

  Generally it is enough to set it to a few seconds, as most clients send the
  full request immediately upon connection. Add 3 or more seconds to cover TCP
  retransmits but that's all. Setting it to very low values (eg: 50 ms) will
  generally work on local networks as long as there are no packet losses. This
  will prevent people from sending bare HTTP requests using telnet.

  If this parameter is not set, the client timeout still applies between each
  chunk of the incoming request.

  See also : "timeout client".


timeout queue <timeout>
  Set the maximum time to wait in the queue for a connection slot to be free
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments :
    <timeout> is the timeout value specified in milliseconds by default, but
              can be in any other unit if the number is suffixed by the unit,
              as explained at the top of this document.

  When a server's maxconn is reached, connections are left pending in a queue
  which may be server-specific or global to the backend. In order not to wait
  indefinitely, a timeout is applied to requests pending in the queue. If the
  timeout is reached, it is considered that the request will almost never be
  served, so it is dropped and a 503 error is returned to the client.

  The "timeout queue" statement allows to fix the maximum time for a request to
  be left pending in a queue. If unspecified, the same value as the backend's
  connection timeout ("timeout connect") is used, for backwards compatibility
  with older versions with no "timeout queue" parameter.

  See also : "timeout connect", "contimeout".


timeout server <timeout>
timeout srvtimeout <timeout> (deprecated)
  Set the maximum inactivity time on the server side.
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments :
    <timeout> is the timeout value specified in milliseconds by default, but
              can be in any other unit if the number is suffixed by the unit,
              as explained at the top of this document.

  The inactivity timeout applies when the server is expected to acknowledge or
  send data. In HTTP mode, this timeout is particularly important to consider
  during the first phase of the server's response, when it has to send the
  headers, as it directly represents the server's processing time for the
  request. To find out what value to put there, it's often good to start with
  what would be considered as unacceptable response times, then check the logs
  to observe the response time distribution, and adjust the value accordingly.

  The value is specified in milliseconds by default, but can be in any other
  unit if the number is suffixed by the unit, as specified at the top of this
  document. In TCP mode (and to a lesser extent, in HTTP mode), it is highly
  recommended that the client timeout remains equal to the server timeout in
  order to avoid complex situations to debug. Whatever the expected server
  response times, it is a good practice to cover at least one or several TCP
  packet losses by specifying timeouts that are slightly above multiples of 3
  seconds (eg: 4 or 5 seconds minimum). 

  This parameter is specific to backends, but can be specified once for all in
  "defaults" sections. This is in fact one of the easiest solutions not to
  forget about it. An unspecified timeout results in an infinite timeout, which
  is not recommended. Such a usage is accepted and works but reports a warning
  during startup because it may results in accumulation of expired sessions in
  the system if the system's timeouts are not configured either.

  This parameter replaces the old, deprecated "srvtimeout". It is recommended
  to use it to write new configurations. The form "timeout srvtimeout" is
  provided only by backwards compatibility but its use is strongly discouraged.

  See also : "srvtimeout", "timeout client".


timeout tarpit <timeout>
  Set the duration for which tapitted connections will be maintained
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments :
    <timeout> is the tarpit duration specified in milliseconds by default, but
              can be in any other unit if the number is suffixed by the unit,
              as explained at the top of this document.

  When a connection is tarpitted using "reqtarpit", it is maintained open with
  no activity for a certain amount of time, then closed. "timeout tarpit"
  defines how long it will be maintained open.

  The value is specified in milliseconds by default, but can be in any other
  unit if the number is suffixed by the unit, as specified at the top of this
  document. If unspecified, the same value as the backend's connection timeout
  ("timeout connect") is used, for backwards compatibility with older versions
  with no "timeout tapit" parameter. 

  See also : "timeout connect", "contimeout".


transparent (deprecated)
  Enable client-side transparent proxying
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments : none

  This keyword was introduced in order to provide layer 7 persistence to layer
  3 load balancers. The idea is to use the OS's ability to redirect an incoming
  connection for a remote address to a local process (here HAProxy), and let
  this process know what address was initially requested. When this option is
  used, sessions without cookies will be forwarded to the original destination
  IP address of the incoming request (which should match that of another
  equipment), while requests with cookies will still be forwarded to the
  appropriate server.

  The "transparent" keyword is deprecated, use "option transparent" instead.

  Note that contrary to a common belief, this option does NOT make HAProxy
  present the client's IP to the server when establishing the connection.

  See also: "option transparent"


use_backend <backend> if <condition>
use_backend <backend> unless <condition>
  Switch to a specific backend if/unless a Layer 7 condition is matched.
  May be used in sections :   defaults | frontend | listen | backend
                                  no   |    yes   |   yes  |   no
  Arguments :
    <backend>   is the name of a valid backend or "listen" section.

    <condition> is a condition composed of ACLs, as described in section 2.3.

  When doing content-switching, connections arrive on a frontend and are then
  dispatched to various backends depending on a number of conditions. The
  relation between the conditions and the backends is described with the
  "use_backend" keyword. This is supported only in HTTP mode.

  There may be as many "use_backend" rules as desired. All of these rules are
  evaluated in their declaration order, and the first one which matches will
  assign the backend.

  In the first form, the backend will be used if the condition is met. In the
  second form, the backend will be used if the condition is not met. If no
  condition is valid, the backend defined with "default_backend" will be used.
  If no default backend is defined, either the servers in the same section are
  used (in case of a "listen" section) or, in case of a frontend, no server is
  used and a 503 service unavailable response is returned.

  See also: "default_backend" and section 2.3 about ACLs.
  

2.3) Using ACLs
---------------

The use of Access Control Lists (ACL) provides a flexible solution to perform
content switching and generally to take decisions based on content extracted
from the request, the response or any environmental status. The principle is
simple :

  - define test criteria with sets of values
  - perform actions only if a set of tests is valid

The actions generally consist in blocking the request, or selecting a backend.

In order to define a test, the "acl" keyword is used. The syntax is :

   acl <aclname> <criterion> [flags] [operator] <value> ...

This creates a new ACL <aclname> or completes an existing one with new tests.
Those tests apply to the portion of request/response specified in <criterion>
and may be adjusted with optional flags [flags]. Some criteria also support
an operator which may be specified before the set of values. The values are
of the type supported by the criterion, and are separated by spaces.

ACL names must be formed from upper and lower case letters, digits, '-' (dash),
'_' (underscore) , '.' (dot) and ':' (colon). ACL names are case-sensitive,
which means that "my_acl" and "My_Acl" are two different ACLs.

There is no enforced limit to the number of ACLs. The unused ones do not affect
performance, they just consume a small amount of memory.

The following ACL flags are currently supported :

   -i : ignore case during matching.
   -- : force end of flags. Useful when a string looks like one of the flags.

Supported types of values are :

  - integers or integer ranges
  - strings
  - regular expressions
  - IP addresses and networks


2.3.1) Matching integers
------------------------

Matching integers is special in that ranges and operators are permitted. Note
that integer matching only applies to positive values. A range is a value
expressed with a lower and an upper bound separated with a colon, both of which
may be omitted.

For instance, "1024:65535" is a valid range to represent a range of
unprivileged ports, and "1024:" would also work. "0:1023" is a valid
representation of privileged ports, and ":1023" would also work.

As a special case, some ACL functions support decimal numbers which are in fact
two integers separated by a dot. This is used with some version checks for
instance. All integer properties apply to those decimal numbers, including
ranges and operators.

For an easier usage, comparison operators are also supported. Note that using
operators with ranges does not make much sense and is strongly discouraged.
Similarly, it does not make much sense to perform order comparisons with a set
of values.

Available operators for integer matching are :

  eq : true if the tested value equals at least one value
  ge : true if the tested value is greater than or equal to at least one value
  gt : true if the tested value is greater than at least one value
  le : true if the tested value is less than or equal to at least one value
  lt : true if the tested value is less than at least one value

For instance, the following ACL matches any negative Content-Length header :

  acl negative-length hdr_val(content-length) lt 0

This one matches SSL versions between 3.0 and 3.1 (inclusive) :

  acl sslv3 req_ssl_ver 3:3.1


2.3.2) Matching strings
-----------------------

String matching applies to verbatim strings as they are passed, with the
exception of the backslash ("\") which makes it possible to escape some
characters such as the space. If the "-i" flag is passed before the first
string, then the matching will be performed ignoring the case. In order
to match the string "-i", either set it second, or pass the "--" flag
before the first string. Same applies of course to match the string "--".


2.3.3) Matching regular expressions (regexes)
---------------------------------------------

Just like with string matching, regex matching applies to verbatim strings as
they are passed, with the exception of the backslash ("\") which makes it
possible to escape some characters such as the space. If the "-i" flag is
passed before the first regex, then the matching will be performed ignoring
the case. In order to match the string "-i", either set it second, or pass
the "--" flag before the first string. Same principle applies of course to
match the string "--".


2.3.4) Matching IPv4 addresses
------------------------------

IPv4 addresses values can be specified either as plain addresses or with a
netmask appended, in which case the IPv4 address matches whenever it is
within the network. Plain addresses may also be replaced with a resolvable
host name, but this practice is generally discouraged as it makes it more
difficult to read and debug configurations. If hostnames are used, you should
at least ensure that they are present in /etc/hosts so that the configuration
does not depend on any random DNS match at the moment the configuration is
parsed.


2.3.5) Available matching criteria
----------------------------------

2.3.5.1) Matching at Layer 4 and below
--------------------------------------

A first set of criteria applies to information which does not require any
analysis of the request or response contents. Those generally include TCP/IP
addresses and ports, as well as internal values independant on the stream.

always_false
  This one never matches. All values and flags are ignored. It may be used as
  a temporary replacement for another one when adjusting configurations.

always_true
  This one always matches. All values and flags are ignored. It may be used as
  a temporary replacement for another one when adjusting configurations.

src <ip_address>
  Applies to the client's IPv4 address. It is usually used to limit access to
  certain resources such as statistics. Note that it is the TCP-level source
  address which is used, and not the address of a client behind a proxy.

src_port <integer>
  Applies to the client's TCP source port. This has a very limited usage.

dst <ip_address>
  Applies to the local IPv4 address the client connected to. It can be used to
  switch to a different backend for some alternative addresses.

dst_port <integer>
  Applies to the local port the client connected to. It can be used to switch
  to a different backend for some alternative ports.

dst_conn <integer>
  Applies to the number of currently established connections on the frontend,
  including the one being evaluated. It can be used to either return a sorry
  page before hard-blocking, or to use a specific backend to drain new requests
  when the farm is considered saturated.

nbsrv <integer>
nbsrv(backend) <integer>
  Returns true when the number of usable servers of either the current backend
  or the named backend matches the values or ranges specified. This is used to
  switch to an alternate backend when the number of servers is too low to
  to handle some load. It is useful to report a failure when combined with
  "monitor fail".

connslots <integer>
connslots(backend) <integer>
  The basic idea here is to be able to measure the number of connection "slots"
  still available (connection, + queue) - so that anything beyond that (intended
  usage; see "use_backend" keyword) can be redirected to a different backend.

  'connslots' = number of available server connection slots, + number of available
  server queue slots.

  *Note that while "dst_conn" may be used, "connslots" comes in especially useful
  when you have a case of traffic going to one single ip, splitting into multiple
  backends (perhaps using acls to do name-based load balancing) - and you want to
  be able to differentiate between different backends, and their "connslots"
  available.  Also, whereas "nbsrv" only measures servers that are actually *down*,
  this acl is more fine-grained - and looks into the number of conn slots available
  as well.

  *OTHER CAVEATS AND NOTES: at this point in time, the code does not take care of
  dynamic connections. Also, if any of the server maxconn, or maxqueue is 0, then
  this acl clearly does not make sense - in which case the value returned will be -1.

fe_sess_rate <integer>
fe_sess_rate(frontend) <integer>
  Returns true when the session creation rate on the current or the named
  frontend matches the specified values or ranges, expressed in new sessions
  per second. This is used to limit the connection rate to acceptable ranges in
  order to prevent abuse of service at the earliest moment. This can be
  combined with layer 4 ACLs in order to force the clients to wait a bit for
  the rate to go down below the limit.

  Example :
        # This frontend limits incoming mails to 10/s with a max of 100
        # concurrent connections. We accept any connection below 10/s, and
        # force excess clients to wait for 100 ms. Since clients are limited to
        # 100 max, there cannot be more than 10 incoming mails per second.
        frontend mail
            bind :25
            mode tcp
            maxconn 100
            acl too_fast fe_sess_rate ge 10
            tcp-request inspect-delay 100ms
            tcp-request content accept if ! too_fast
            tcp-request content accept if WAIT_END
  
be_sess_rate <integer>
be_sess_rate(backend) <integer>
  Returns true when the sessions creation rate on the backend matches the
  specified values or ranges, in number of new sessions per second. This is
  used to switch to an alternate backend when an expensive or fragile one
  reaches too high a session rate, or to limite abuse of service (eg. prevent
  sucking of an online dictionary).

  Example :
        # Redirect to an error page if the dictionary is requested too often
        backend dynamic
            mode http
            acl being_scanned be_sess_rate gt 100
            redirect location /denied.html if being_scanned


2.3.5.2) Matching contents at Layer 4
-------------------------------------

A second set of criteria depends on data found in buffers, but which can change
during analysis. This requires that some data has been buffered, for instance
through TCP request content inspection. Please see the "tcp-request" keyword
for more detailed information on the subject.

req_len <integer>
  Returns true when the lenght of the data in the request buffer matches the
  specified range. It is important to understand that this test does not
  return false as long as the buffer is changing. This means that a check with
  equality to zero will almost always immediately match at the beginning of the
  session, while a test for more data will wait for that data to come in and
  return false only when haproxy is certain that no more data will come in.
  This test was designed to be used with TCP request content inspection.

req_ssl_ver <decimal>
  Returns true when data in the request buffer look like SSL, with a protocol
  version matching the specified range. Both SSLv2 hello messages and SSLv3
  messages are supported. The test tries to be strict enough to avoid being
  easily fooled. In particular, it waits for as many bytes as announced in the
  message header if this header looks valid (bound to the buffer size). Note
  that TLSv1 is announced as SSL version 3.1. This test was designed to be used
  with TCP request content inspection.

wait_end
  Waits for the end of the analysis period to return true. This may be used in
  conjunction with content analysis to avoid returning a wrong verdict early.
  It may also be used to delay some actions, such as a delayed reject for some
  special addresses. Since it either stops the rules evaluation or immediately
  returns true, it is recommended to use this acl as the last one in a rule.
  Please note that the default ACL "WAIT_END" is always usable without prior
  declaration. This test was designed to be used with TCP request content
  inspection.

  Examples :
     # delay every incoming request by 2 seconds
     tcp-request inspect-delay 2s
     tcp-request content accept if WAIT_END

     # don't immediately tell bad guys they are rejected
     tcp-request inspect-delay 10s
     acl goodguys src 10.0.0.0/24
     acl badguys  src 10.0.1.0/24
     tcp-request content accept if goodguys
     tcp-request content reject if badguys WAIT_END
     tcp-request content reject


2.3.5.3) Matching at Layer 7
----------------------------

A third set of criteria applies to information which can be found at the
application layer (layer 7). Those require that a full HTTP request has been
read, and are only evaluated then. They may require slightly more CPU resources
than the layer 4 ones, but not much since the request and response are indexed.

method <string>
  Applies to the method in the HTTP request, eg: "GET". Some predefined ACL
  already check for most common methods.

req_ver <string>
  Applies to the version string in the HTTP request, eg: "1.0". Some predefined
  ACL already check for versions 1.0 and 1.1.

path <string>
  Returns true when the path part of the request, which starts at the first
  slash and ends before the question mark, equals one of the strings. It may be
  used to match known files, such as /favicon.ico.

path_beg <string>
  Returns true when the path begins with one of the strings. This can be used
  to send certain directory names to alternative backends.

path_end <string>
  Returns true when the path ends with one of the strings. This may be used to
  control file name extension.

path_sub <string>
  Returns true when the path contains one of the strings. It can be used to
  detect particular patterns in paths, such as "../" for example. See also
  "path_dir".

path_dir <string>
  Returns true when one of the strings is found isolated or delimited with
  slashes in the path. This is used to perform filename or directory name
  matching without the risk of wrong match due to colliding prefixes. See also
  "url_dir" and "path_sub".

path_dom <string>
  Returns true when one of the strings is found isolated or delimited with dots
  in the path. This may be used to perform domain name matching in proxy
  requests. See also "path_sub" and "url_dom".

path_reg <regex>
  Returns true when the path matches one of the regular expressions. It can be
  used any time, but it is important to remember that regex matching is slower
  than other methods. See also "url_reg" and all "path_" criteria.

url <string>
  Applies to the whole URL passed in the request. The only real use is to match
  "*", for which there already is a predefined ACL.

url_beg <string>
  Returns true when the URL begins with one of the strings. This can be used to
  check whether a URL begins with a slash or with a protocol scheme.

url_end <string>
  Returns true when the URL ends with one of the strings. It has very limited
  use. "path_end" should be used instead for filename matching.

url_sub <string>
  Returns true when the URL contains one of the strings. It can be used to
  detect particular patterns in query strings for example. See also "path_sub".

url_dir <string>
  Returns true when one of the strings is found isolated or delimited with
  slashes in the URL. This is used to perform filename or directory name
  matching without the risk of wrong match due to colliding prefixes. See also
  "path_dir" and "url_sub".

url_dom <string>
  Returns true when one of the strings is found isolated or delimited with dots
  in the URL. This is used to perform domain name matching without the risk of
  wrong match due to colliding prefixes. See also "url_sub".

url_reg <regex>
  Returns true when the URL matches one of the regular expressions. It can be
  used any time, but it is important to remember that regex matching is slower
  than other methods. See also "path_reg" and all "url_" criteria.

url_ip <ip_address>
  Applies to the IP address specified in the absolute URI in an HTTP request.
  It can be used to prevent access to certain resources such as local network.
  It is useful with option "http_proxy".

url_port <integer>
  Applies to the port specified in the absolute URI in an HTTP request. It can
  be used to prevent access to certain resources. It is useful with option
  "http_proxy". Note that if the port is not specified in the request, port 80
  is assumed.

hdr <string> 
hdr(header) <string>
  Note: all the "hdr*" matching criteria either apply to all headers, or to a
  particular header whose name is passed between parenthesis and without any
  space. The header name is not case-sensitive. The header matching complies
  with RFC2616, and treats as separate headers all values delimited by commas.

  The "hdr" criteria returns true if any of the headers matching the criteria
  match any of the strings. This can be used to check exact for values. For
  instance, checking that "connection: close" is set :

     hdr(Connection) -i close

hdr_beg <string>
hdr_beg(header) <string>
  Returns true when one of the headers begins with one of the strings. See
  "hdr" for more information on header matching.

hdr_end <string>
hdr_end(header) <string>
  Returns true when one of the headers ends with one of the strings. See "hdr"
  for more information on header matching.

hdr_sub <string>
hdr_sub(header) <string>
  Returns true when one of the headers contains one of the strings. See "hdr"
  for more information on header matching.

hdr_dir <string>
hdr_dir(header) <string>
  Returns true when one of the headers contains one of the strings either
  isolated or delimited by slashes. This is used to perform filename or
  directory name matching, and may be used with Referer. See "hdr" for more
  information on header matching.

hdr_dom <string>
hdr_dom(header) <string>
  Returns true when one of the headers contains one of the strings either
  isolated or delimited by dots. This is used to perform domain name matching,
  and may be used with the Host header. See "hdr" for more information on
  header matching.

hdr_reg <regex>
hdr_reg(header) <regex>
  Returns true when one of the headers matches of the regular expressions. It
  can be used at any time, but it is important to remember that regex matching
  is slower than other methods. See also other "hdr_" criteria, as well as
  "hdr" for more information on header matching.

hdr_val <integer>
hdr_val(header) <integer>
  Returns true when one of the headers starts with a number which matches the
  values or ranges specified. This may be used to limit content-length to
  acceptable values for example. See "hdr" for more information on header
  matching.

hdr_cnt <integer>
hdr_cnt(header) <integer>
  Returns true when the number of occurrence of the specified header matches
  the values or ranges specified. It is important to remember that one header
  line may count as several headers if it has several values. This is used to
  detect presence, absence or abuse of a specific header, as well as to block
  request smugling attacks by rejecting requests which contain more than one
  of certain headers. See "hdr" for more information on header matching.


2.3.6) Pre-defined ACLs
-----------------------

Some predefined ACLs are hard-coded so that they do not have to be declared in
every frontend which needs them. They all have their names in upper case in
order to avoid confusion. Their equivalence is provided below. Please note that
only the first three ones are not layer 7 based.

ACL name          Equivalent to                Usage
---------------+-----------------------------+---------------------------------
TRUE             always_true                   always match
FALSE            always_false                  never match
LOCALHOST        src 127.0.0.1/8               match connection from local host
HTTP_1.0         req_ver 1.0                   match HTTP version 1.0
HTTP_1.1         req_ver 1.1                   match HTTP version 1.1
METH_CONNECT     method  CONNECT               match HTTP CONNECT method
METH_GET         method  GET HEAD              match HTTP GET or HEAD method
METH_HEAD        method  HEAD                  match HTTP HEAD method
METH_OPTIONS     method  OPTIONS               match HTTP OPTIONS method
METH_POST        method  POST                  match HTTP POST method
METH_TRACE       method  TRACE                 match HTTP TRACE method
HTTP_URL_ABS     url_reg ^[^/:]*://            match absolute URL with scheme
HTTP_URL_SLASH   url_beg /                     match URL begining with "/"
HTTP_URL_STAR    url     *                     match URL equal to "*"
HTTP_CONTENT     hdr_val(content-length) gt 0  match an existing content-length
REQ_CONTENT      req_len gt 0                  match data in the request buffer
WAIT_END         wait_end                      wait for end of content analysis
---------------+-----------------------------+---------------------------------


2.3.7) Using ACLs to form conditions
------------------------------------

Some actions are only performed upon a valid condition. A condition is a
combination of ACLs with operators. 3 operators are supported :

  - AND (implicit)
  - OR  (explicit with the "or" keyword or the "||" operator)
  - Negation with the exclamation mark ("!")

A condition is formed as a disjonctive form :

   [!]acl1 [!]acl2 ... [!]acln  { or [!]acl1 [!]acl2 ... [!]acln } ...

Such conditions are generally used after an "if" or "unless" statement,
indicating when the condition will trigger the action.

For instance, to block HTTP requests to the "*" URL with methods other than
"OPTIONS", as well as POST requests without content-length, and GET or HEAD
requests with a content-length greater than 0, and finally every request which
is not either GET/HEAD/POST/OPTIONS !

   acl missing_cl hdr_cnt(Content-length) eq 0
   block if HTTP_URL_STAR !METH_OPTIONS || METH_POST missing_cl
   block if METH_GET HTTP_CONTENT
   block unless METH_GET or METH_POST or METH_OPTIONS

To select a different backend for requests to static contents on the "www" site
and to every request on the "img", "video", "download" and "ftp" hosts :

   acl url_static  path_beg         /static /images /img /css
   acl url_static  path_end         .gif .png .jpg .css .js
   acl host_www    hdr_beg(host) -i www
   acl host_static hdr_beg(host) -i img. video. download. ftp.

   # now use backend "static" for all static-only hosts, and for static urls
   # of host "www". Use backend "www" for the rest.
   use_backend static if host_static or host_www url_static
   use_backend www    if host_www

See section 2.2 for detailed help on the "block" and "use_backend" keywords.


2.4) Server options
-------------------

The "server" keyword supports a certain number of settings which are all passed
as arguments on the server line. The order in which those arguments appear does
not count, and they are all optional. Some of those settings are single words
(booleans) while others expect one or several values after them. In this case,
the values must immediately follow the setting name. All those settings must be
specified after the server's address if they are used :

  server <name> <address>[:port] [settings ...]

The currently supported settings are the following ones.

addr <ipv4>
  Using the "addr" parameter, it becomes possible to use a different IP address
  to send health-checks. On some servers, it may be desirable to dedicate an IP
  address to specific component able to perform complex tests which are more
  suitable to health-checks than the application. This parameter is ignored if
  the "check" parameter is not set. See also the "port" parameter.

backup
  When "backup" is present on a server line, the server is only used in load
  balancing when all other non-backup servers are unavailable. Requests coming
  with a persistence cookie referencing the server will always be served
  though. By default, only the first operational backup server is used, unless
  the "allbackups" option is set in the backend. See also the "allbackups"
  option.

check
  This option enables health checks on the server. By default, a server is
  always considered available. If "check" is set, the server will receive
  periodic health checks to ensure that it is really able to serve requests.
  The default address and port to send the tests to are those of the server,
  and the default source is the same as the one defined in the backend. It is
  possible to change the address using the "addr" parameter, the port using the
  "port" parameter, the source address using the "source" address, and the
  interval and timers using the "inter", "rise" and "fall" parameters. The
  request method is define in the backend using the "httpchk", "smtpchk",
  and "ssl-hello-chk" options. Please refer to those options and parameters for
  more information.

cookie <value>
  The "cookie" parameter sets the cookie value assigned to the server to
  <value>. This value will be checked in incoming requests, and the first
  operational server possessing the same value will be selected. In return, in
  cookie insertion or rewrite modes, this value will be assigned to the cookie
  sent to the client. There is nothing wrong in having several servers sharing
  the same cookie value, and it is in fact somewhat common between normal and
  backup servers. See also the "cookie" keyword in backend section.

fall <count>
  The "fall" parameter states that a server will be considered as dead after
  <count> consecutive unsuccessful health checks. This value defaults to 3 if
  unspecified. See also the "check", "inter" and "rise" parameters.

id <value>
  Set a persistent value for server ID. Must be unique and larger than 1000, as
  smaller values are reserved for auto-assigned ids.

inter <delay>
fastinter <delay>
downinter <delay>
  The "inter" parameter sets the interval between two consecutive health checks
  to <delay> milliseconds. If left unspecified, the delay defaults to 2000 ms.
  It is also possible to use "fastinter" and "downinter" to optimize delays
  between checks depending on the server state :

             Server state            |             Interval used
    ---------------------------------+-----------------------------------------
     UP 100% (non-transitional)      | "inter"
    ---------------------------------+-----------------------------------------
     Transitionally UP (going down), |
     Transitionally DOWN (going up), | "fastinter" if set, "inter" otherwise.
     or yet unchecked.               |
    ---------------------------------+-----------------------------------------
     DOWN 100% (non-transitional)    | "downinter" if set, "inter" otherwise.
    ---------------------------------+-----------------------------------------
    
  Just as with every other time-based parameter, they can be entered in any
  other explicit unit among { us, ms, s, m, h, d }. The "inter" parameter also
  serves as a timeout for health checks sent to servers if "timeout check" is
  not set. In order to reduce "resonance" effects when multiple servers are
  hosted on the same hardware, the health-checks of all servers are started
  with a small time offset between them. It is also possible to add some random
  noise in the health checks interval using the global "spread-checks"
  keyword. This makes sense for instance when a lot of backends use the same
  servers.

maxconn <maxconn>
  The "maxconn" parameter specifies the maximal number of concurrent
  connections that will be sent to this server. If the number of incoming
  concurrent requests goes higher than this value, they will be queued, waiting
  for a connection to be released. This parameter is very important as it can
  save fragile servers from going down under extreme loads. If a "minconn"
  parameter is specified, the limit becomes dynamic. The default value is "0"
  which means unlimited. See also the "minconn" and "maxqueue" parameters, and
  the backend's "fullconn" keyword.

maxqueue <maxqueue>
  The "maxqueue" parameter specifies the maximal number of connections which
  will wait in the queue for this server. If this limit is reached, next
  requests will be redispatched to other servers instead of indefinitely
  waiting to be served. This will break persistence but may allow people to
  quickly re-log in when the server they try to connect to is dying. The
  default value is "0" which means the queue is unlimited. See also the
  "maxconn" and "minconn" parameters.

minconn <minconn>
  When the "minconn" parameter is set, the maxconn limit becomes a dynamic
  limit following the backend's load. The server will always accept at least
  <minconn> connections, never more than <maxconn>, and the limit will be on
  the ramp between both values when the backend has less than <fullconn>
  concurrent connections. This makes it possible to limit the load on the
  server during normal loads, but push it further for important loads without
  overloading the server during exceptionnal loads. See also the "maxconn"
  and "maxqueue" parameters, as well as the "fullconn" backend keyword.
  
port <port>
  Using the "port" parameter, it becomes possible to use a different port to
  send health-checks. On some servers, it may be desirable to dedicate a port
  to a specific component able to perform complex tests which are more suitable
  to health-checks than the application. It is common to run a simple script in
  inetd for instance. This parameter is ignored if the "check" parameter is not
  set. See also the "addr" parameter.

redir <prefix>
  The "redir" parameter enables the redirection mode for all GET and HEAD
  requests addressing this server. This means that instead of having HAProxy
  forward the request to the server, it will send an "HTTP 302" response with
  the "Location" header composed of this prefix immediately followed by the
  requested URI beginning at the leading '/' of the path component. That means
  that no trailing slash should be used after <prefix>. All invalid requests
  will be rejected, and all non-GET or HEAD requests will be normally served by
  the server. Note that since the response is completely forged, no header
  mangling nor cookie insertion is possible in the respose. However, cookies in
  requests are still analysed, making this solution completely usable to direct
  users to a remote location in case of local disaster. Main use consists in
  increasing bandwidth for static servers by having the clients directly
  connect to them. Note: never use a relative location here, it would cause a
  loop between the client and HAProxy!

  Example :  server srv1 192.168.1.1:80 redir http://image1.mydomain.com check

rise <count>
  The "rise" parameter states that a server will be considered as operational
  after <count> consecutive successful health checks. This value defaults to 2
  if unspecified. See also the "check", "inter" and "fall" parameters.

slowstart <start_time_in_ms>
  The "slowstart" parameter for a server accepts a value in milliseconds which
  indicates after how long a server which has just come back up will run at
  full speed. Just as with every other time-based parameter, it can be entered
  in any other explicit unit among { us, ms, s, m, h, d }. The speed grows
  linearly from 0 to 100% during this time. The limitation applies to two
  parameters :

  - maxconn: the number of connections accepted by the server will grow from 1
    to 100% of the usual dynamic limit defined by (minconn,maxconn,fullconn).

  - weight: when the backend uses a dynamic weighted algorithm, the weight
    grows linearly from 1 to 100%. In this case, the weight is updated at every
    health-check. For this reason, it is important that the "inter" parameter
    is smaller than the "slowstart", in order to maximize the number of steps.

  The slowstart never applies when haproxy starts, otherwise it would cause
  trouble to running servers. It only applies when a server has been previously
  seen as failed.

source <addr>[:<port>] [usesrc { <addr2>[:<port2>] | client | clientip } ]
source <addr>[:<port>] [interface <name>] ...
  The "source" parameter sets the source address which will be used when
  connecting to the server. It follows the exact same parameters and principle
  as the backend "source" keyword, except that it only applies to the server
  referencing it. Please consult the "source" keyword for details.

track [<proxy>/]<server>
  This option enables ability to set the current state of the server by
  tracking another one. Only a server with checks enabled can be tracked
  so it is not possible for example to track a server that tracks another
  one. If <proxy> is omitted the current one is used. If disable-on-404 is
  used, it has to be enabled on both proxies.

weight <weight>
  The "weight" parameter is used to adjust the server's weight relative to
  other servers. All servers will receive a load proportional to their weight
  relative to the sum of all weights, so the higher the weight, the higher the
  load. The default weight is 1, and the maximal value is 255. If this
  parameter is used to distribute the load according to server's capacity, it
  is recommended to start with values which can both grow and shrink, for
  instance between 10 and 100 to leave enough room above and below for later
  adjustments.


2.5) HTTP header manipulation
-----------------------------

In HTTP mode, it is possible to rewrite, add or delete some of the request and
response headers based on regular expressions. It is also possible to block a
request or a response if a particular header matches a regular expression,
which is enough to stop most elementary protocol attacks, and to protect
against information leak from the internal network. But there is a limitation
to this : since HAProxy's HTTP engine does not support keep-alive, only headers
passed during the first request of a TCP session will be seen. All subsequent
headers will be considered data only and not analyzed. Furthermore, HAProxy
never touches data contents, it stops analysis at the end of headers.

This section covers common usage of the following keywords, described in detail
in section 2.2.1 :

  - reqadd     <string>
  - reqallow   <search>
  - reqiallow  <search>
  - reqdel     <search>
  - reqidel    <search>
  - reqdeny    <search>
  - reqideny   <search>
  - reqpass    <search>
  - reqipass   <search>
  - reqrep     <search> <replace>
  - reqirep    <search> <replace>
  - reqtarpit  <search>
  - reqitarpit <search>
  - rspadd     <string>
  - rspdel     <search>
  - rspidel    <search>
  - rspdeny    <search>
  - rspideny   <search>
  - rsprep     <search> <replace>
  - rspirep    <search> <replace>

With all these keywords, the same conventions are used. The <search> parameter
is a POSIX extended regular expression (regex) which supports grouping through
parenthesis (without the backslash). Spaces and other delimiters must be
prefixed with a backslash ('\') to avoid confusion with a field delimiter.
Other characters may be prefixed with a backslash to change their meaning :

  \t   for a tab
  \r   for a carriage return (CR)
  \n   for a new line (LF)
  \    to mark a space and differentiate it from a delimiter
  \#   to mark a sharp and differentiate it from a comment
  \\   to use a backslash in a regex
  \\\\ to use a backslash in the text (*2 for regex, *2 for haproxy)
  \xXX to write the ASCII hex code XX as in the C language

The <replace> parameter contains the string to be used to replace the largest
portion of text matching the regex. It can make use of the special characters
above, and can reference a substring which is delimited by parenthesis in the
regex, by writing a backslash ('\') immediately followed by one digit from 0 to
9 indicating the group position (0 designating the entire line). This practice
is very common to users of the "sed" program.

The <string> parameter represents the string which will systematically be added
after the last header line. It can also use special character sequences above.

Notes related to these keywords :
---------------------------------
  - these keywords are not always convenient to allow/deny based on header
    contents. It is strongly recommended to use ACLs with the "block" keyword
    instead, resulting in far more flexible and manageable rules.

  - lines are always considered as a whole. It is not possible to reference
    a header name only or a value only. This is important because of the way
    headers are written (notably the number of spaces after the colon).

  - the first line is always considered as a header, which makes it possible to
    rewrite or filter HTTP requests URIs or response codes, but in turn makes
    it harder to distinguish between headers and request line. The regex prefix
    ^[^\ \t]*[\ \t] matches any HTTP method followed by a space, and the prefix
    ^[^ \t:]*: matches any header name followed by a colon.

  - for performances reasons, the number of characters added to a request or to
    a response is limited at build time to values between 1 and 4 kB. This
    should normally be far more than enough for most usages. If it is too short
    on occasional usages, it is possible to gain some space by removing some
    useless headers before adding new ones.

  - keywords beginning with "reqi" and "rspi" are the same as their couterpart
    without the 'i' letter except that they ignore case when matching patterns.

  - when a request passes through a frontend then a backend, all req* rules
    from the frontend will be evaluated, then all req* rules from the backend
    will be evaluated. The reverse path is applied to responses.

  - req* statements are applied after "block" statements, so that "block" is
    always the first one, but before "use_backend" in order to permit rewriting
    before switching. 


2.6) Logging
------------

One of HAProxy's strong points certainly lies is its precise logs. It probably
provides the finest level of information available for such a product, which is
very important for troubleshooting complex environments. Standard information
provided in logs include client ports, TCP/HTTP state timers, precise session
state at termination and precise termination cause, information about decisions
to direct trafic to a server, and of course the ability to capture arbitrary
headers.

In order to improve administrators reactivity, it offers a great transparency
about encountered problems, both internal and external, and it is possible to
send logs to different sources at the same time with different level filters :

  - global process-level logs (system errors, start/stop, etc..)
  - per-instance system and internal errors (lack of resource, bugs, ...)
  - per-instance external troubles (servers up/down, max connections)
  - per-instance activity (client connections), either at the establishment or
    at the termination.

The ability to distribute different levels of logs to different log servers
allow several production teams to interact and to fix their problems as soon
as possible. For example, the system team might monitor system-wide errors,
while the application team might be monitoring the up/down for their servers in
real time, and the security team might analyze the activity logs with one hour
delay.


2.6.1) Log levels
-----------------

TCP and HTTP connections can be logged with informations such as date, time,
source IP address, destination address, connection duration, response times,
HTTP request, the HTTP return code, number of bytes transmitted, the conditions
in which the session ended, and even exchanged cookies values, to track a
particular user's problems for example. All messages are sent to up to two
syslog servers. Check the "log" keyword in section 2.2 for more info about log
facilities.


2.6.2) Log formats
------------------

HAProxy supports 3 log formats. Several fields are common between these formats
and will be detailed in the next sections. A few of them may slightly vary with
the configuration, due to indicators specific to certain options. The supported
formats are the following ones :

  - the default format, which is very basic and very rarely used. It only
    provides very basic information about the incoming connection at the moment
    it is accepted : source IP:port, destination IP:port, and frontend-name.
    This mode will eventually disappear so it will not be described to great
    extents.

  - the TCP format, which is more advanced. This format is enabled when "option
    tcplog" is set on the frontend. HAProxy will then usually wait for the
    connection to terminate before logging. This format provides much richer
    information, such as timers, connection counts, queue size, etc... This
    format is recommended for pure TCP proxies.

  - the HTTP format, which is the most advanced for HTTP proxying. This format
    is enabled when "option httplog" is set on the frontend. It provides the
    same information as the TCP format with some HTTP-specific fields such as
    the request, the status code, and captures of headers and cookies. This
    format is recommended for HTTP proxies.

Next sections will go deeper into details for each of these formats. Format
specification will be performed on a "field" basis. Unless stated otherwise, a
field is a portion of text delimited by any number of spaces. Since syslog
servers are susceptible of inserting fields at the beginning of a line, it is
always assumed that the first field is the one containing the process name and
identifier.

Note : Since log lines may be quite long, the log examples in sections below
       might be broken into multiple lines. The example log lines will be
       prefixed with 3 closing angle brackets ('>>>') and each time a log is
       broken into multiple lines, each non-final line will end with a
       backslash ('\') and the next line will start indented by two characters.


2.6.2.1) Default log format
---------------------------

This format is used when no specific option is set. The log is emitted as soon
as the connection is accepted. One should note that this currently is the only
format which logs the request's destination IP and ports.

  Example :
        listen www
            mode http
            log global
            server srv1 127.0.0.1:8000

    >>> Feb  6 12:12:09 localhost \
          haproxy[14385]: Connect from 10.0.1.2:33312 to 10.0.3.31:8012 \
          (www/HTTP)

  Field   Format                                Extract from the example above
      1   process_name '[' pid ']:'                            haproxy[14385]:
      2   'Connect from'                                          Connect from
      3   source_ip ':' source_port                             10.0.1.2:33312
      4   'to'                                                              to
      5   destination_ip ':' destination_port                   10.0.3.31:8012
      6   '(' frontend_name '/' mode ')'                            (www/HTTP)

Detailed fields description :
  - "source_ip" is the IP address of the client which initiated the connection.
  - "source_port" is the TCP port of the client which initiated the connection.
  - "destination_ip" is the IP address the client connected to.
  - "destination_port" is the TCP port the client connected to.
  - "frontend_name" is the name of the frontend (or listener) which received
    and processed the connection.
  - "mode is the mode the frontend is operating (TCP or HTTP).

It is advised not to use this deprecated format for newer installations as it
will eventually disappear.


2.6.2.2) TCP log format
-----------------------

The TCP format is used when "option tcplog" is specified in the frontend, and
is the recommended format for pure TCP proxies. It provides a lot of precious
information for troubleshooting. Since this format includes timers and byte
counts, the log is normally emitted at the end of the session. It can be
emitted earlier if "option logasap" is specified, which makes sense in most
environments with long sessions such as remote terminals. Sessions which match
the "monitor" rules are never logged. It is also possible not to emit logs for
sessions for which no data were exchanged between the client and the server, by
specifying "option dontlognull" in the frontend. A few fields may slightly vary
depending on some configuration options, those are marked with a star ('*')
after the field name below.

  Example :
        frontend fnt
            mode tcp
            option tcplog
            log global
            default_backend bck

        backend bck
            server srv1 127.0.0.1:8000

    >>> Feb  6 12:12:56 localhost \
          haproxy[14387]: 10.0.1.2:33313 [06/Feb/2009:12:12:51.443] fnt \
          bck/srv1 0/0/5007 212 -- 0/0/0/0/3 0/0

  Field   Format                                Extract from the example above
      1   process_name '[' pid ']:'                            haproxy[14387]:
      2   client_ip ':' client_port                             10.0.1.2:33313
      3   '[' accept_date ']'                       [06/Feb/2009:12:12:51.443]
      4   frontend_name                                                    fnt
      5   backend_name '/' server_name                                bck/srv1
      6   Tw '/' Tc '/' Tt*                                           0/0/5007
      7   bytes_read*                                                      212
      8   termination_state                                                 --
      9   actconn '/' feconn '/' beconn '/' srv_conn '/' retries*    0/0/0/0/3
     10   srv_queue '/' backend_queue                                      0/0

Detailed fields description :
  - "client_ip" is the IP address of the client which initiated the TCP
    connection to haproxy.

  - "client_port" is the TCP port of the client which initiated the connection.

  - "accept_date" is the exact date when the connection was received by haproxy
    (which might be very slightly different from the date observed on the
    network if there was some queuing in the system's backlog). This is usually
    the same date which may appear in any upstream firewall's log.

  - "frontend_name" is the name of the frontend (or listener) which received
    and processed the connection.

  - "backend_name" is the name of the backend (or listener) which was selected
    to manage the connection to the server. This will be the same as the
    frontend if no switching rule has been applied, which is common for TCP
    applications.

  - "server_name" is the name of the last server to which the connection was
    sent, which might differ from the first one if there were connection errors
    and a redispatch occurred. Note that this server belongs to the backend
    which processed the request. If the connection was aborted before reaching
    a server, "<NOSRV>" is indicated instead of a server name.

  - "Tw" is the total time in milliseconds spent waiting in the various queues.
    It can be "-1" if the connection was aborted before reaching the queue.
    See "Timers" below for more details.

  - "Tc" is the total time in milliseconds spent waiting for the connection to
    establish to the final server, including retries. It can be "-1" if the
    connection was aborted before a connection could be established. See
    "Timers" below for more details.

  - "Tt" is the total time in milliseconds elapsed between the accept and the
    last close. It covers all possible processings. There is one exception, if
    "option logasap" was specified, then the time counting stops at the moment
    the log is emitted. In this case, a '+' sign is prepended before the value,
    indicating that the final one will be larger. See "Timers" below for more
    details.

  - "bytes_read" is the total number of bytes transmitted from the server to
    the client when the log is emitted. If "option logasap" is specified, the
    this value will be prefixed with a '+' sign indicating that the final one
    may be larger. Please note that this value is a 64-bit counter, so log
    analysis tools must be able to handle it without overflowing.

  - "termination_state" is the condition the session was in when the session
    ended. This indicates the session state, which side caused the end of
    session to happen, and for what reason (timeout, error, ...). The normal
    flags should be "--", indicating the session was closed by either end with
    no data remaining in buffers. See below "Session state at disconnection"
    for more details.

  - "actconn" is the total number of concurrent connections on the process when
    the session was logged. It it useful to detect when some per-process system
    limits have been reached. For instance, if actconn is close to 512 when
    multiple connection errors occur, chances are high that the system limits
    the process to use a maximum of 1024 file descriptors and that all of them
    are used. See section 1 "Global parameters" to find how to tune the system.

  - "feconn" is the total number of concurrent connections on the frontend when
    the session was logged. It is useful to estimate the amount of resource
    required to sustain high loads, and to detect when the frontend's "maxconn"
    has been reached. Most often when this value increases by huge jumps, it is
    because there is congestion on the backend servers, but sometimes it can be
    caused by a denial of service attack.

  - "beconn" is the total number of concurrent connections handled by the
    backend when the session was logged. It includes the total number of
    concurrent connections active on servers as well as the number of
    connections pending in queues. It is useful to estimate the amount of
    additional servers needed to support high loads for a given application.
    Most often when this value increases by huge jumps, it is because there is
    congestion on the backend servers, but sometimes it can be caused by a
    denial of service attack.

  - "srv_conn" is the total number of concurrent connections still active on
    the server when the session was logged. It can never exceed the server's
    configured "maxconn" parameter. If this value is very often close or equal
    to the server's "maxconn", it means that traffic regulation is involved a
    lot, meaning that either the server's maxconn value is too low, or that
    there aren't enough servers to process the load with an optimal response
    time. When only one of the server's "srv_conn" is high, it usually means
    that this server has some trouble causing the connections to take longer to
    be processed than on other servers.

  - "retries" is the number of connection retries experienced by this session
    when trying to connect to the server. It must normally be zero, unless a
    server is being stopped at the same moment the connection was attempted.
    Frequent retries generally indicate either a network problem between
    haproxy and the server, or a misconfigured system backlog on the server
    preventing new connections from being queued. This field may optionally be
    prefixed with a '+' sign, indicating that the session has experienced a
    redispatch after the maximal retry count has been reached on the initial
    server. In this case, the server name appearing in the log is the one the
    connection was redispatched to, and not the first one, though both may
    sometimes be the same in case of hashing for instance. So as a general rule
    of thumb, when a '+' is present in front of the retry count, this count
    should not be attributed to the logged server.

  - "srv_queue" is the total number of requests which were processed before
    this one in the server queue. It is zero when the request has not gone
    through the server queue. It makes it possible to estimate the approximate
    server's response time by dividing the time spent in queue by the number of
    requests in the queue. It is worth noting that if a session experiences a
    redispatch and passes through two server queues, their positions will be
    cumulated. A request should not pass through both the server queue and the
    backend queue unless a redispatch occurs.

  - "backend_queue" is the total number of requests which were processed before
    this one in the backend's global queue. It is zero when the request has not
    gone through the global queue. It makes it possible to estimate the average
    queue length, which easily translates into a number of missing servers when
    divided by a server's "maxconn" parameter. It is worth noting that if a
    session experiences a redispatch, it may pass twice in the backend's queue,
    and then both positions will be cumulated. A request should not pass
    through both the server queue and the backend queue unless a redispatch
    occurs.


2.6.2.3) HTTP log format
------------------------

The HTTP format is the most complete and the best suited for HTTP proxies. It
is enabled by when "option httplog" is specified in the frontend. It provides
the same level of information as the TCP format with additional features which
are specific to the HTTP protocol. Just like the TCP format, the log is usually
emitted at the end of the session, unless "option logasap" is specified, which
generally only makes sense for download sites. A session which matches the
"monitor" rules will never logged. It is also possible not to log sessions for
which no data were sent by the client by specifying "option dontlognull" in the
frontend.

Most fields are shared with the TCP log, some being different. A few fields may
slightly vary depending on some configuration options. Those ones are marked
with a star ('*') after the field name below.

  Example :
        frontend http-in
            mode http
            option httplog
            log global
            default_backend bck

        backend static
            server srv1 127.0.0.1:8000

    >>> Feb  6 12:14:14 localhost \
          haproxy[14389]: 10.0.1.2:33317 [06/Feb/2009:12:14:14.655] http-in \
          static/srv1 10/0/30/69/109 200 2750 - - ---- 1/1/1/1/0 0/0 {1wt.eu} \
          {} "GET /index.html HTTP/1.1" 

  Field   Format                                Extract from the example above
      1   process_name '[' pid ']:'                            haproxy[14389]:
      2   client_ip ':' client_port                             10.0.1.2:33317
      3   '[' accept_date ']'                       [06/Feb/2009:12:14:14.655]
      4   frontend_name                                                http-in
      5   backend_name '/' server_name                             static/srv1
      6   Tq '/' Tw '/' Tc '/' Tr '/' Tt*                       10/0/30/69/109
      7   status_code                                                      200
      8   bytes_read*                                                     2750
      9   captured_request_cookie                                            -
     10   captured_response_cookie                                           -
     11   termination_state                                               ----
     12   actconn '/' feconn '/' beconn '/' srv_conn '/' retries*    1/1/1/1/0
     13   srv_queue '/' backend_queue                                      0/0
     14   '{' captured_request_headers* '}'                   {haproxy.1wt.eu}
     15   '{' captured_response_headers* '}'                                {}
     16   '"' http_request '"'                      "GET /index.html HTTP/1.1"
  

Detailed fields description :
  - "client_ip" is the IP address of the client which initiated the TCP
    connection to haproxy.

  - "client_port" is the TCP port of the client which initiated the connection.

  - "accept_date" is the exact date when the TCP connection was received by
    haproxy (which might be very slightly different from the date observed on
    the network if there was some queuing in the system's backlog). This is
    usually the same date which may appear in any upstream firewall's log. This
    does not depend on the fact that the client has sent the request or not.

  - "frontend_name" is the name of the frontend (or listener) which received
    and processed the connection.

  - "backend_name" is the name of the backend (or listener) which was selected
    to manage the connection to the server. This will be the same as the
    frontend if no switching rule has been applied.

  - "server_name" is the name of the last server to which the connection was
    sent, which might differ from the first one if there were connection errors
    and a redispatch occurred. Note that this server belongs to the backend
    which processed the request. If the request was aborted before reaching a
    server, "<NOSRV>" is indicated instead of a server name. If the request was
    intercepted by the stats subsystem, "<STATS>" is indicated instead.

  - "Tq" is the total time in milliseconds spent waiting for the client to send
    a full HTTP request, not counting data. It can be "-1" if the connection
    was aborted before a complete request could be received. It should always
    be very small because a request generally fits in one single packet. Large
    times here generally indicate network trouble between the client and
    haproxy. See "Timers" below for more details.

  - "Tw" is the total time in milliseconds spent waiting in the various queues.
    It can be "-1" if the connection was aborted before reaching the queue.
    See "Timers" below for more details.

  - "Tc" is the total time in milliseconds spent waiting for the connection to
    establish to the final server, including retries. It can be "-1" if the
    request was aborted before a connection could be established. See "Timers"
    below for more details.

  - "Tr" is the total time in milliseconds spent waiting for the server to send
    a full HTTP response, not counting data. It can be "-1" if the request was
    aborted before a complete response could be received. It generally matches
    the server's processing time for the request, though it may be altered by
    the amount of data sent by the client to the server. Large times here on
    "GET" requests generally indicate an overloaded server. See "Timers" below
    for more details.

  - "Tt" is the total time in milliseconds elapsed between the accept and the
    last close. It covers all possible processings. There is one exception, if
    "option logasap" was specified, then the time counting stops at the moment
    the log is emitted. In this case, a '+' sign is prepended before the value,
    indicating that the final one will be larger. See "Timers" below for more
    details.

  - "status_code" is the HTTP status code returned to the client. This status
    is generally set by the server, but it might also be set by haproxy when
    the server cannot be reached or when its response is blocked by haproxy.

  - "bytes_read" is the total number of bytes transmitted to the client when
    the log is emitted. This does include HTTP headers. If "option logasap" is
    specified, the this value will be prefixed with a '+' sign indicating that
    the final one may be larger. Please note that this value is a 64-bit
    counter, so log analysis tools must be able to handle it without
    overflowing.

  - "captured_request_cookie" is an optional "name=value" entry indicating that
    the client had this cookie in the request. The cookie name and its maximum
    length are defined by the "capture cookie" statement in the frontend
    configuration. The field is a single dash ('-') when the option is not
    set. Only one cookie may be captured, it is generally used to track session
    ID exchanges between a client and a server to detect session crossing
    between clients due to application bugs. For more details, please consult
    the section "Capturing HTTP headers and cookies" below.

  - "captured_response_cookie" is an optional "name=value" entry indicating
    that the server has returned a cookie with its response. The cookie name
    and its maximum length are defined by the "capture cookie" statement in the
    frontend configuration. The field is a single dash ('-') when the option is
    not set. Only one cookie may be captured, it is generally used to track
    session ID exchanges between a client and a server to detect session
    crossing between clients due to application bugs. For more details, please
    consult the section "Capturing HTTP headers and cookies" below.

  - "termination_state" is the condition the session was in when the session
    ended. This indicates the session state, which side caused the end of
    session to happen, for what reason (timeout, error, ...), just like in TCP
    logs, and information about persistence operations on cookies in the last
    two characters. The normal flags should begin with "--", indicating the
    session was closed by either end with no data remaining in buffers. See
    below "Session state at disconnection" for more details.

  - "actconn" is the total number of concurrent connections on the process when
    the session was logged. It it useful to detect when some per-process system
    limits have been reached. For instance, if actconn is close to 512 or 1024
    when multiple connection errors occur, chances are high that the system
    limits the process to use a maximum of 1024 file descriptors and that all
    of them are used. See section 1 "Global parameters" to find how to tune the
    system.

  - "feconn" is the total number of concurrent connections on the frontend when
    the session was logged. It is useful to estimate the amount of resource
    required to sustain high loads, and to detect when the frontend's "maxconn"
    has been reached. Most often when this value increases by huge jumps, it is
    because there is congestion on the backend servers, but sometimes it can be
    caused by a denial of service attack.

  - "beconn" is the total number of concurrent connections handled by the
    backend when the session was logged. It includes the total number of
    concurrent connections active on servers as well as the number of
    connections pending in queues. It is useful to estimate the amount of
    additional servers needed to support high loads for a given application.
    Most often when this value increases by huge jumps, it is because there is
    congestion on the backend servers, but sometimes it can be caused by a
    denial of service attack.

  - "srv_conn" is the total number of concurrent connections still active on
    the server when the session was logged. It can never exceed the server's
    configured "maxconn" parameter. If this value is very often close or equal
    to the server's "maxconn", it means that traffic regulation is involved a
    lot, meaning that either the server's maxconn value is too low, or that
    there aren't enough servers to process the load with an optimal response
    time. When only one of the server's "srv_conn" is high, it usually means
    that this server has some trouble causing the requests to take longer to be
    processed than on other servers.

  - "retries" is the number of connection retries experienced by this session
    when trying to connect to the server. It must normally be zero, unless a
    server is being stopped at the same moment the connection was attempted.
    Frequent retries generally indicate either a network problem between
    haproxy and the server, or a misconfigured system backlog on the server
    preventing new connections from being queued. This field may optionally be
    prefixed with a '+' sign, indicating that the session has experienced a
    redispatch after the maximal retry count has been reached on the initial
    server. In this case, the server name appearing in the log is the one the
    connection was redispatched to, and not the first one, though both may
    sometimes be the same in case of hashing for instance. So as a general rule
    of thumb, when a '+' is present in front of the retry count, this count
    should not be attributed to the logged server.

  - "srv_queue" is the total number of requests which were processed before
    this one in the server queue. It is zero when the request has not gone
    through the server queue. It makes it possible to estimate the approximate
    server's response time by dividing the time spent in queue by the number of
    requests in the queue. It is worth noting that if a session experiences a
    redispatch and passes through two server queues, their positions will be
    cumulated. A request should not pass through both the server queue and the
    backend queue unless a redispatch occurs.

  - "backend_queue" is the total number of requests which were processed before
    this one in the backend's global queue. It is zero when the request has not
    gone through the global queue. It makes it possible to estimate the average
    queue length, which easily translates into a number of missing servers when
    divided by a server's "maxconn" parameter. It is worth noting that if a
    session experiences a redispatch, it may pass twice in the backend's queue,
    and then both positions will be cumulated. A request should not pass
    through both the server queue and the backend queue unless a redispatch
    occurs.

  - "captured_request_headers" is a list of headers captured in the request due
    to the presence of the "capture request header" statement in the frontend.
    Multiple headers can be captured, they will be delimited by a vertical bar
    ('|'). When no capture is enabled, the braces do not appear, causing a
    shift of remaining fields. It is important to note that this field may
    contain spaces, and that using it requires a smarter log parser than when
    it's not used. Please consult the section "Capturing HTTP headers and
    cookies" below for more details.

  - "captured_response_headers" is a list of headers captured in the response
    due to the presence of the "capture response header" statement in the
    frontend. Multiple headers can be captured, they will be delimited by a
    vertical bar ('|'). When no capture is enabled, the braces do not appear,
    causing a shift of remaining fields. It is important to note that this
    field may contain spaces, and that using it requires a smarter log parser
    than when it's not used. Please consult the section "Capturing HTTP headers
    and cookies" below for more details.

  - "http_request" is the complete HTTP request line, including the method,
    request and HTTP version string. Non-printable characters are encoded (see
    below the section "Non-printable characters"). This is always the last
    field, and it is always delimited by quotes and is the only one which can
    contain quotes. If new fields are added to the log format, they will be
    added before this field. This field might be truncated if the request is
    huge and does not fit in the standard syslog buffer (1024 characters). This
    is the reason why this field must always remain the last one.


2.6.3) Advanced logging options
-------------------------------

Some advanced logging options are often looked for but are not easy to find out
just by looking at the various options. Here is an entry point for the few
options which can enable better logging. Please refer to the keywords reference
for more information about their usage.


2.6.3.1) Disabling logging of external tests
--------------------------------------------

It is quite common to have some monitoring tools perform health checks on
haproxy. Sometimes it will be a layer 3 load-balancer such as LVS or any
commercial load-balancer, and sometimes it will simply be a more complete
monitoring system such as Nagios. When the tests are very frequent, users often
ask how to disable logging for those checks. There are three possibilities :

  - if connections come from everywhere and are just TCP probes, it is often
    desired to simply disable logging of connections without data exchange, by
    setting "option dontlognull" in the frontend. It also disables logging of
    port scans, which may or may not be desired.

  - if the connection come from a known source network, use "monitor-net" to
    declare this network as monitoring only. Any host in this network will then
    only be able to perform health checks, and their requests will not be
    logged. This is generally appropriate to designate a list of equipments
    such as other load-balancers.

  - if the tests are performed on a known URI, use "monitor-uri" to declare
    this URI as dedicated to monitoring. Any host sending this request will
    only get the result of a health-check, and the request will not be logged.


2.6.3.2) Logging before waiting for the session to terminate
------------------------------------------------------------

The problem with logging at end of connection is that you have no clue about
what is happening during very long sessions, such as remote terminal sessions
or large file downloads. This problem can be worked around by specifying
"option logasap" in the frontend. Haproxy will then log as soon as possible,
just before data transfer begins. This means that in case of TCP, it will still
log the connection status to the server, and in case of HTTP, it will log just
after processing the server headers. In this case, the number of bytes reported
is the number of header bytes sent to the client. In order to avoid confusion
with normal logs, the total time field and the number of bytes are prefixed
with a '+' sign which means that real numbers are certainly larger.


2.6.4) Timing events
--------------------

Timers provide a great help in troubleshooting network problems. All values are
reported in milliseconds (ms). These timers should be used in conjunction with
the session termination flags. In TCP mode with "option tcplog" set on the
frontend, 3 control points are reported under the form "Tw/Tc/Tt", and in HTTP
mode, 5 control points are reported under the form "Tq/Tw/Tc/Tr/Tt" :

  - Tq: total time to get the client request (HTTP mode only). It's the time
    elapsed between the moment the client connection was accepted and the
    moment the proxy received the last HTTP header. The value "-1" indicates
    that the end of headers (empty line) has never been seen. This happens when
    the client closes prematurely or times out.

  - Tw: total time spent in the queues waiting for a connection slot. It
    accounts for backend queue as well as the server queues, and depends on the
    queue size, and the time needed for the server to complete previous
    requests. The value "-1" means that the request was killed before reaching
    the queue, which is generally what happens with invalid or denied requests.

  - Tc: total time to establish the TCP connection to the server. It's the time
    elapsed between the moment the proxy sent the connection request, and the
    moment it was acknowledged by the server, or between the TCP SYN packet and
    the matching SYN/ACK packet in return. The value "-1" means that the
    connection never established.

  - Tr: server response time (HTTP mode only). It's the time elapsed between
    the moment the TCP connection was established to the server and the moment
    the server sent its complete response headers. It purely shows its request
    processing time, without the network overhead due to the data transmission.
    It is worth noting that when the client has data to send to the server, for
    instance during a POST request, the time already runs, and this can distort
    apparent response time. For this reason, it's generally wise not to trust
    too much this field for POST requests initiated from clients behind an
    untrusted network. A value of "-1" here means that the last the response
    header (empty line) was never seen, most likely because the server timeout
    stroke before the server managed to process the request.

  - Tt: total session duration time, between the moment the proxy accepted it
    and the moment both ends were closed. The exception is when the "logasap"
    option is specified. In this case, it only equals (Tq+Tw+Tc+Tr), and is
    prefixed with a '+' sign. From this field, we can deduce "Td", the data
    transmission time, by substracting other timers when valid :

        Td = Tt - (Tq + Tw + Tc + Tr)

    Timers with "-1" values have to be excluded from this equation. In TCP
    mode, "Tq" and "Tr" have to be excluded too. Note that "Tt" can never be
    negative.

These timers provide precious indications on trouble causes. Since the TCP
protocol defines retransmit delays of 3, 6, 12... seconds, we know for sure
that timers close to multiples of 3s are nearly always related to lost packets
due to network problems (wires, negociation, congestion). Moreover, if "Tt" is
close to a timeout value specified in the configuration, it often means that a
session has been aborted on timeout.

Most common cases :

  - If "Tq" is close to 3000, a packet has probably been lost between the
    client and the proxy. This is very rare on local networks but might happen
    when clients are on far remote networks and send large requests. It may
    happen that values larger than usual appear here without any network cause.
    Sometimes, during an attack or just after a resource starvation has ended,
    haproxy may accept thousands of connections in a few milliseconds. The time
    spent accepting these connections will inevitably slightly delay processing
    of other connections, and it can happen that request times in the order of
    a few tens of milliseconds are measured after a few thousands of new
    connections have been accepted at once.

  - If "Tc" is close to 3000, a packet has probably been lost between the
    server and the proxy during the server connection phase. This value should
    always be very low, such as 1 ms on local networks and less than a few tens
    of ms on remote networks.

  - If "Tr" is nearly always lower than 3000 except some rare values which seem to
    be the average majored by 3000, there are probably some packets lost between
    the proxy and the server.

  - If "Tt" is large even for small byte counts, it generally is because
    neither the client nor the server decides to close the connection, for
    instance because both have agreed on a keep-alive connection mode. In order
    to solve this issue, it will be needed to specify "option httpclose" on
    either the frontend or the backend. If the problem persists, it means that
    the server ignores the "close" connection mode and expects the client to
    close. Then it will be required to use "option forceclose". Having the
    smallest possible 'Tt' is important when connection regulation is used with
    the "maxconn" option on the servers, since no new connection will be sent
    to the server until another one is released.

Other noticeable HTTP log cases ('xx' means any value to be ignored) :

  Tq/Tw/Tc/Tr/+Tt  The "option logasap" is present on the frontend and the log
                   was emitted before the data phase. All the timers are valid
                   except "Tt" which is shorter than reality.

  -1/xx/xx/xx/Tt   The client was not able to send a complete request in time
                   or it aborted too early. Check the session termination flags
                   then "timeout http-request" and "timeout client" settings.

  Tq/-1/xx/xx/Tt   It was not possible to process the request, maybe because
                   servers were out of order, because the request was invalid
                   or forbidden by ACL rules. Check the session termination
                   flags.

  Tq/Tw/-1/xx/Tt   The connection could not establish on the server. Either it
                   actively refused it or it timed out after Tt-(Tq+Tw) ms.
                   Check the session termination flags, then check the
                   "timeout connect" setting. Note that the tarpit action might
                   return similar-looking patterns, with "Tw" equal to the time
                   the client connection was maintained open.

  Tq/Tw/Tc/-1/Tt   The server has accepted the connection but did not return
                   a complete response in time, or it closed its connexion
                   unexpectedly after Tt-(Tq+Tw+Tc) ms. Check the session
                   termination flags, then check the "timeout server" setting.


2.6.5) Session state at disconnection
-------------------------------------

TCP and HTTP logs provide a session termination indicator in the
"termination_state" field, just before the number of active connections. It is
2-characters long in TCP mode, and is extended to 4 characters in HTTP mode,
each of which has a special meaning :

  - On the first character, a code reporting the first event which caused the
    session to terminate :

        C : the TCP session was unexpectedly aborted by the client.

        S : the TCP session was unexpectedly aborted by the server, or the
            server explicitly refused it.

        P : the session was prematurely aborted by the proxy, because of a
            connection limit enforcement, because a DENY filter was matched,
            because of a security check which detected and blocked a dangerous
            error in server response which might have caused information leak
            (eg: cacheable cookie), or because the response was processed by
            the proxy (redirect, stats, etc...).

        R : a resource on the proxy has been exhausted (memory, sockets, source
            ports, ...). Usually, this appears during the connection phase, and
            system logs should contain a copy of the precise error. If this
            happens, it must be considered as a very serious anomaly which
            should be fixed as soon as possible by any means.

        I : an internal error was identified by the proxy during a self-check.
            This should NEVER happen, and you are encouraged to report any log
            containing this, because this would almost certainly be a bug. It
            would be wise to preventively restart the process after such an
            event too, in case it would be caused by memory corruption.

        c : the client-side timeout expired while waiting for the client to
            send or receive data.

        s : the server-side timeout expired while waiting for the server to
            send or receive data.

        - : normal session completion, both the client and the server closed
            with nothing left in the buffers.

  - on the second character, the TCP or HTTP session state when it was closed :

        R : th proxy was waiting for a complete, valid REQUEST from the client
            (HTTP mode only). Nothing was sent to any server.

        Q : the proxy was waiting in the QUEUE for a connection slot. This can
            only happen when servers have a 'maxconn' parameter set. It can
            also happen in the global queue after a redispatch consecutive to
            a failed attempt to connect to a dying server. If no redispatch is
            reported, then no connection attempt was made to any server.

        C : the proxy was waiting for the CONNECTION to establish on the
            server. The server might at most have noticed a connection attempt.

        H : the proxy was waiting for complete, valid response HEADERS from the
            server (HTTP only).

        D : the session was in the DATA phase.

        L : the proxy was still transmitting LAST data to the client while the
            server had already finished. This one is very rare as it can only
            happen when the client dies while receiving the last packets.

        T : the request was tarpitted. It has been held open with the client
            during the whole "timeout tarpit" duration or until the client
            closed, both of which will be reported in the "Tw" timer.

        - : normal session completion after end of data transfer.

  - the third character tells whether the persistence cookie was provided by
    the client (only in HTTP mode) :

        N : the client provided NO cookie. This is usually the case for new
            visitors, so counting the number of occurrences of this flag in the
            logs generally indicate a valid trend for the site frequentation.

        I : the client provided an INVALID cookie matching no known server.
            This might be caused by a recent configuration change, mixed
            cookies between HTTP/HTTPS sites, or an attack.

        D : the client provided a cookie designating a server which was DOWN,
            so either "option persist" was used and the client was sent to
            this server, or it was not set and the client was redispatched to
            another server.

        V : the client provided a valid cookie, and was sent to the associated
            server.

        - : does not apply (no cookie set in configuration).

  - the last character reports what operations were performed on the persistence
    cookie returned by the server (only in HTTP mode) :

        N : NO cookie was provided by the server, and none was inserted either.

        I : no cookie was provided by the server, and the proxy INSERTED one.
            Note that in "cookie insert" mode, if the server provides a cookie,
            it will still be overwritten and reported as "I" here.

        P : a cookie was PROVIDED by the server and transmitted as-is.

        R : the cookie provided by the server was REWRITTEN by the proxy, which
            happens in "cookie rewrite" or "cookie prefix" modes.

        D : the cookie provided by the server was DELETED by the proxy.

        - : does not apply (no cookie set in configuration).

The combination of the two first flags give a lot of information about what was
happening when the session terminated, and why it did terminate. It can be
helpful to detect server saturation, network troubles, local system resource
starvation, attacks, etc...

The most common termination flags combinations are indicated below. They are
alphabetically sorted, with the lowercase set just after the upper case for
easier finding and understanding.

  Flags   Reason

     --   Normal termination.

     CC   The client aborted before the connection could be established to the
          server. This can happen when haproxy tries to connect to a recently
          dead (or unchecked) server, and the client aborts while haproxy is
          waiting for the server to respond or for "timeout connect" to expire.

     CD   The client unexpectedly aborted during data transfer. This can be
          caused by a browser crash, by an intermediate equipment between the
          client and haproxy which decided to actively break the connection,
          by network routing issues between the client and haproxy, or by a
          keep-alive session between the server and the client terminated first
          by the client.
	  
     cD   The client did not send nor acknowledge any data for as long as the
          "timeout client" delay. This is often caused by network failures on
	  the client side, or the client simply leaving the net uncleanly.

     CH   The client aborted while waiting for the server to start responding.
          It might be the server taking too long to respond or the client
          clicking the 'Stop' button too fast.

     cH   The "timeout client" stroke while waiting for client data during a
          POST request. This is sometimes caused by too large TCP MSS values
          for PPPoE networks which cannot transport full-sized packets. It can
          also happen when client timeout is smaller than server timeout and
          the server takes too long to respond.

     CQ   The client aborted while its session was queued, waiting for a server
          with enough empty slots to accept it. It might be that either all the
          servers were saturated or that the assigned server was taking too
          long a time to respond.

     CR   The client aborted before sending a full HTTP request. Most likely
          the request was typed by hand using a telnet client, and aborted
          too early. The HTTP status code is likely a 400 here. Sometimes this
          might also be caused by an IDS killing the connection between haproxy
          and the client.

     cR   The "timeout http-request" stroke before the client sent a full HTTP
          request. This is sometimes caused by too large TCP MSS values on the
          client side for PPPoE networks which cannot transport full-sized
          packets, or by clients sending requests by hand and not typing fast
          enough, or forgetting to enter the empty line at the end of the
          request. The HTTP status code is likely a 408 here.

     CT   The client aborted while its session was tarpitted. It is important to
          check if this happens on valid requests, in order to be sure that no
          wrong tarpit rules have been written. If a lot of them happen, it might
          make sense to lower the "timeout tarpit" value to something closer to
          the average reported "Tw" timer, in order not to consume resources for
          just a few attackers.

     SC   The server or an equipement between it and haproxy explicitly refused
          the TCP connection (the proxy received a TCP RST or an ICMP message
          in return). Under some circumstances, it can also be the network
          stack telling the proxy that the server is unreachable (eg: no route,
          or no ARP response on local network). When this happens in HTTP mode,
          the status code is likely a 502 or 503 here.

     sC   The "timeout connect" stroke before a connection to the server could
          complete. When this happens in HTTP mode, the status code is likely a
          503 or 504 here.

     SD   The connection to the server died with an error during the data
          transfer. This usually means that haproxy has received an RST from
          the server or an ICMP message from an intermediate equipment while
          exchanging data with the server. This can be caused by a server crash
          or by a network issue on an intermediate equipment.

     sD   The server did not send nor acknowledge any data for as long as the
          "timeout server" setting during the data phase. This is often caused
          by too short timeouts on L4 equipements before the server (firewalls,
          load-balancers, ...), as well as keep-alive sessions maintained
          between the client and the server expiring first on haproxy.

     SH   The server aborted before sending its full HTTP response headers, or
          it crashed while processing the request. Since a server aborting at
          this moment is very rare, it would be wise to inspect its logs to
          control whether it crashed and why. The logged request may indicate a
          small set of faulty requests, demonstrating bugs in the application.
          Sometimes this might also be caused by an IDS killing the connection
          between haproxy and the server.

     sH   The "timeout server" stroke before the server could return its
          response headers. This is the most common anomaly, indicating too
          long transactions, probably caused by server or database saturation.
          The immediate workaround consists in increasing the "timeout server"
          setting, but it is important to keep in mind that the user experience
          will suffer from these long response times. The only long term
          solution is to fix the application.

     sQ   The session spent too much time in queue and has been expired. See
          the "timeout queue" and "timeout connect" settings to find out how to
          fix this if it happens too often. If it often happens massively in
          short periods, it may indicate general problems on the affected
          servers due to I/O or database congestion, or saturation caused by
          external attacks.

     PC   The proxy refused to establish a connection to the server because the
          process' socket limit has been reached while attempting to connect.
	  The global "maxconn" parameter may be increased in the configuration
          so that it does not happen anymore. This status is very rare and
          might happen when the global "ulimit-n" parameter is forced by hand.

     PH   The proxy blocked the server's response, because it was invalid,
          incomplete, dangerous (cache control), or matched a security filter.
          In any case, an HTTP 502 error is sent to the client. One possible
          cause for this error is an invalid syntax in an HTTP header name
          containing unauthorized characters.

     PR   The proxy blocked the client's HTTP request, either because of an
          invalid HTTP syntax, in which case it returned an HTTP 400 error to
          the client, or because a deny filter matched, in which case it
          returned an HTTP 403 error.

     PT   The proxy blocked the client's request and has tarpitted its
          connection before returning it a 500 server error. Nothing was sent
          to the server. The connection was maintained open for as long as
          reported by the "Tw" timer field.

     RC   A local resource has been exhausted (memory, sockets, source ports)
          preventing the connection to the server from establishing. The error
          logs will tell precisely what was missing. This is very rare and can
          only be solved by proper system tuning.


2.6.6) Non-printable characters
-------------------------------

In order not to cause trouble to log analysis tools or terminals during log
consulting, non-printable characters are not sent as-is into log files, but are
converted to the two-digits hexadecimal representation of their ASCII code,
prefixed by the character '#'. The only characters that can be logged without
being escaped are comprised between 32 and 126 (inclusive). Obviously, the
escape character '#' itself is also encoded to avoid any ambiguity ("#23"). It
is the same for the character '"' which becomes "#22", as well as '{', '|' and
'}' when logging headers.

Note that the space character (' ') is not encoded in headers, which can cause
issues for tools relying on space count to locate fields. A typical header
containing spaces is "User-Agent".

Last, it has been observed that some syslog daemons such as syslog-ng escape
the quote ('"') with a backslash ('\'). The reverse operation can safely be
performed since no quote may appear anywhere else in the logs.


2.6.7) Capturing HTTP cookies
-----------------------------

Cookie capture simplifies the tracking a complete user session. This can be
achieved using the "capture cookie" statement in the frontend. Please refer to
section 2.2 for more details. Only one cookie can be captured, and the same
cookie will simultaneously be checked in the request ("Cookie:" header) and in
the response ("Set-Cookie:" header). The respective values will be reported in
the HTTP logs at the "captured_request_cookie" and "captured_response_cookie"
locations (see section 2.6.2.3 about HTTP log format). When either cookie is
not seen, a dash ('-') replaces the value. This way, it's easy to detect when a
user switches to a new session for example, because the server will reassign it
a new cookie. It is also possible to detect if a server unexpectedly sets a
wrong cookie to a client, leading to session crossing.

  Examples :
        # capture the first cookie whose name starts with "ASPSESSION"
        capture cookie ASPSESSION len 32

        # capture the first cookie whose name is exactly "vgnvisitor"
        capture cookie vgnvisitor= len 32


2.6.8) Capturing HTTP headers
-----------------------------

Header captures are useful to track unique request identifiers set by an upper
proxy, virtual host names, user-agents, POST content-length, referrers, etc. In
the response, one can search for information about the response length, how the
server asked the cache to behave, or an object location during a redirection.

Header captures are performed using the "capture request header" and "capture
response header" statements in the frontend. Please consult their definition in
section 2.2 for more details.

It is possible to include both request headers and response headers at the same
time. Non-existant headers are logged as empty strings, and if one header
appears more than once, only its last occurence will be logged. Request headers
are grouped within braces '{' and '}' in the same order as they were declared,
and delimited with a vertical bar '|' without any space. Response headers
follow the same representation, but are displayed after a space following the
request headers block. These blocks are displayed just before the HTTP request
in the logs.

  Example :
        # This instance chains to the outgoing proxy
        listen proxy-out
            mode http
            option httplog
            option logasap
            log global
            server cache1 192.168.1.1:3128

            # log the name of the virtual server
            capture request  header Host len 20

            # log the amount of data uploaded during a POST
            capture request  header Content-Length len 10

            # log the beginning of the referrer
            capture request  header Referer len 20

            # server name (useful for outgoing proxies only)
            capture response header Server len 20

            # logging the content-length is useful with "option logasap"
            capture response header Content-Length len 10

            # log the expected cache behaviour on the response
            capture response header Cache-Control len 8

            # the Via header will report the next proxy's name
            capture response header Via len 20

            # log the URL location during a redirection
            capture response header Location len 20

    >>> Aug  9 20:26:09 localhost \
          haproxy[2022]: 127.0.0.1:34014 [09/Aug/2004:20:26:09] proxy-out \
          proxy-out/cache1 0/0/0/162/+162 200 +350 - - ---- 0/0/0/0/0 0/0 \
          {fr.adserver.yahoo.co||http://fr.f416.mail.} {|864|private||} \
          "GET http://fr.adserver.yahoo.com/"

    >>> Aug  9 20:30:46 localhost \
          haproxy[2022]: 127.0.0.1:34020 [09/Aug/2004:20:30:46] proxy-out \
          proxy-out/cache1 0/0/0/182/+182 200 +279 - - ---- 0/0/0/0/0 0/0 \
          {w.ods.org||} {Formilux/0.1.8|3495|||} \
          "GET http://trafic.1wt.eu/ HTTP/1.1" 

    >>> Aug  9 20:30:46 localhost \
          haproxy[2022]: 127.0.0.1:34028 [09/Aug/2004:20:30:46] proxy-out \
          proxy-out/cache1 0/0/2/126/+128 301 +223 - - ---- 0/0/0/0/0 0/0 \
          {www.sytadin.equipement.gouv.fr||http://trafic.1wt.eu/} \
          {Apache|230|||http://www.sytadin.} \
          "GET http://www.sytadin.equipement.gouv.fr/ HTTP/1.1" 


2.6.9) Examples of logs
-----------------------

These are real-world examples of logs accompanied with an explanation. Some of
them have been made up by hand. The syslog part has been removed for better
reading. Their sole purpose is to explain how to decipher them.

    >>> haproxy[674]: 127.0.0.1:33318 [15/Oct/2003:08:31:57.130] px-http \
          px-http/srv1 6559/0/7/147/6723 200 243 - - ---- 5/3/3/1/0 0/0 \
          "HEAD / HTTP/1.0"

    => long request (6.5s) entered by hand through 'telnet'. The server replied
       in 147 ms, and the session ended normally ('----')

    >>> haproxy[674]: 127.0.0.1:33319 [15/Oct/2003:08:31:57.149] px-http \
          px-http/srv1 6559/1230/7/147/6870 200 243 - - ---- 324/239/239/99/0 \
          0/9 "HEAD / HTTP/1.0"

    => Idem, but the request was queued in the global queue behind 9 other
       requests, and waited there for 1230 ms.

    >>> haproxy[674]: 127.0.0.1:33320 [15/Oct/2003:08:32:17.654] px-http \
          px-http/srv1 9/0/7/14/+30 200 +243 - - ---- 3/3/3/1/0 0/0 \
          "GET /image.iso HTTP/1.0"

    => request for a long data transfer. The "logasap" option was specified, so
       the log was produced just before transfering data. The server replied in
       14 ms, 243 bytes of headers were sent to the client, and total time from
       accept to first data byte is 30 ms.

    >>> haproxy[674]: 127.0.0.1:33320 [15/Oct/2003:08:32:17.925] px-http \
          px-http/srv1 9/0/7/14/30 502 243 - - PH-- 3/2/2/0/0 0/0 \
          "GET /cgi-bin/bug.cgi? HTTP/1.0"

    => the proxy blocked a server response either because of an "rspdeny" or
       "rspideny" filter, or because the response was improperly formatted and
       not HTTP-compliant, or because it blocked sensible information which
       risked being cached. In this case, the response is replaced with a "502
       bad gateway". The flags ("PH--") tell us that it was haproxy who decided
       to return the 502 and not the server.

    >>> haproxy[18113]: 127.0.0.1:34548 [15/Oct/2003:15:18:55.798] px-http \
          px-http/<NOSRV> -1/-1/-1/-1/8490 -1 0 - - CR-- 2/2/2/0/0 0/0 "" 

    => the client never completed its request and aborted itself ("C---") after
       8.5s, while the proxy was waiting for the request headers ("-R--").
       Nothing was sent to any server.

    >>> haproxy[18113]: 127.0.0.1:34549 [15/Oct/2003:15:19:06.103] px-http \
         px-http/<NOSRV> -1/-1/-1/-1/50001 408 0 - - cR-- 2/2/2/0/0 0/0 ""

    => The client never completed its request, which was aborted by the
       time-out ("c---") after 50s, while the proxy was waiting for the request
       headers ("-R--").  Nothing was sent to any server, but the proxy could
       send a 408 return code to the client.

    >>> haproxy[18989]: 127.0.0.1:34550 [15/Oct/2003:15:24:28.312] px-tcp \
          px-tcp/srv1 0/0/5007 0 cD 0/0/0/0/0 0/0

    => This log was produced with "option tcplog". The client timed out after
       5 seconds ("c----").

    >>> haproxy[18989]: 10.0.0.1:34552 [15/Oct/2003:15:26:31.462] px-http \
          px-http/srv1 3183/-1/-1/-1/11215 503 0 - - SC-- 205/202/202/115/3 \
          0/0 "HEAD / HTTP/1.0" 

    => The request took 3s to complete (probably a network problem), and the
       connection to the server failed ('SC--') after 4 attemps of 2 seconds
       (config says 'retries 3'), and no redispatch (otherwise we would have
       seen "/+3"). Status code 503 was returned to the client. There were 115
       connections on this server, 202 connections on this proxy, and 205 on
       the global process. It is possible that the server refused the
       connection because of too many already established.


2.7) CSV format
---------------

The statistics may be consulted either from the unix socket or from the HTTP
page. Both means provide a CSV format whose fields follow.

  0. pxname: proxy name
  1. svname: service name (FRONTEND for frontend, BACKEND for backend, any name
    for server)
  2. qcur: current queued requests
  3. qmax: max queued requests
  4. scur: current sessions
  5. smax: max sessions
  6. slim: sessions limit
  7. stot: total sessions
  8. bin: bytes in
  9. bout: bytes out
 10. dreq: denied requests
 11. dresp: denied responses
 12. ereq: request errors
 13. econ: connection errors
 14. eresp: response errors
 15. wretr: retries (warning)
 16. wredis: redispatches (warning)
 17. status: status (UP/DOWN/...)
 18. weight: server weight (server), total weight (backend)
 19. act: server is active (server), number of active servers (backend)
 20. bck: server is backup (server), number of backup servers (backend)
 21. chkfail: number of failed checks
 22. chkdown: number of UP->DOWN transitions
 23. lastchg: last status change (in seconds)
 24. downtime: total downtime (in seconds)
 25. qlimit: queue limit
 26. pid: process id (0 for first instance, 1 for second, ...)
 27. iid: unique proxy id
 28. sid: service id (unique inside a proxy)
 29. throttle: warm up status
 30. lbtot: total number of times a server was selected
 31. tracked: id of proxy/server if tracking is enabled
 32. type (0=frontend, 1=backend, 2=server)
 33. rate (number of sessions per second over last elapsed second)


2.8) Unix Socket commands
-------------------------

The following commands are supported on the UNIX stats socket ; all of them
must be terminated by a line feed. It is important to understand that when
multiple haproxy processes are started on the same sockets, any process may
pick up the request and will output its own stats.

show stat [<iid> <type> <sid>]
  Dump statistics in the CSV format. By passing <id>, <type> and <sid>, it is
  possible to dump only selected items :
    - <iid> is a proxy ID, -1 to dump everything
    - <type> selects the type of dumpable objects : 1 for frontends, 2 for
       backends, 4 for servers, -1 for everything. These values can be ORed,
       for example:
          1 + 2     = 3   -> frontend + backend.
          1 + 2 + 4 = 7   -> frontend + backend + server.
    - <sid> is a server ID, -1 to dump everything from the selected proxy.

show info
  Dump info about haproxy status on current process.

show sess
  Dump all known sessions. Avoid doing this on slow connections as this can
  be huge.

show errors [<iid>]
  Dump last known request and response errors collected by frontends and
  backends. If <iid> is specified, the limit the dump to errors concerning
  either frontend or backend whose ID is <iid>.

  The errors which may be collected are the last request and response errors
  caused by protocol violations, often due to invalid characters in header
  names. The report precisely indicates what exact character violated the
  protocol. Other important information such as the exact date the error was
  detected, frontend and backend names, the server name (when known), the
  internal session ID and the source address which has initiated the session
  are reported too.

  All characters are returned, and non-printable characters are encoded. The
  most common ones (\t = 9, \n = 10, \r = 13 and \e = 27) are encoded as one
  letter following a backslash. The backslash itself is encoded as '\\' to
  avoid confusion. Other non-printable characters are encoded '\xNN' where
  NN is the two-digits hexadecimal representation of the character's ASCII
  code.

  Lines are prefixed with the position of their first character, starting at 0
  for the beginning of the buffer. At most one input line is printed per line,
  and large lines will be broken into multiple consecutive output lines so that
  the output never goes beyond 79 characters wide. It is easy to detect if a
  line was broken, because it will not end with '\n' and the next line's offset
  will be followed by a '+' sign, indicating it is a continuation of previous
  line.

  Example :
    >>> $ echo "show errors" | socat stdio /tmp/sock1
        [04/Mar/2009:15:46:56.081] backend http-in (#2) : invalid response
          src 127.0.0.1, session #54, frontend fe-eth0 (#1), server s2 (#1)
          response length 213 bytes, error at position 23:

          00000  HTTP/1.0 200 OK\r\n
          00017  header/bizarre:blah\r\n
          00038  Location: blah\r\n
          00054  Long-line: this is a very long line which should b
          00104+ e broken into multiple lines on the output buffer,
          00154+  otherwise it would be too large to print in a ter
          00204+ minal\r\n
          00211  \r\n

    In the example above, we know that the backend "http-in" which has internal
    ID 2 has blocked an invalid response from its server s2 which has internal
    ID 1. The request was on session 54 initiated by source 127.0.0.1 and
    received by frontend fe-eth0 whose ID is 1. The total response length was
    213 bytes when the error was detected, and the error was at byte 23. This
    is the slash ('/') in header name "header/bizarre", which is not a valid
    HTTP character for a header name.

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