doc/configuration.txt

                         ----------------------
                                 HAProxy
                          Configuration Manual
                         ----------------------
                             version 1.5
                             willy tarreau
                              2012/12/28


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.
The summary below is meant to help you search sections by name and navigate
through the document.

Note to documentation contributors :
    This document is formatted 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, indented by two characters. It is also
    sometimes useful to prefix all output lines (logs, console outs) with 3
    closing angle brackets ('>>>') in order to help get the difference between
    inputs and outputs when it can become ambiguous. If you add sections,
    please update the summary below for easier searching.


Summary
-------

1.    Quick reminder about HTTP
1.1.      The HTTP transaction model
1.2.      HTTP request
1.2.1.        The Request line
1.2.2.        The request headers
1.3.      HTTP response
1.3.1.        The Response line
1.3.2.        The response headers

2.    Configuring HAProxy
2.1.      Configuration file format
2.2.      Time format
2.3.      Examples

3.    Global parameters
3.1.      Process management and security
3.2.      Performance tuning
3.3.      Debugging
3.4.      Userlists
3.5.      Peers

4.    Proxies
4.1.      Proxy keywords matrix
4.2.      Alphabetically sorted keywords reference

5.    Bind and Server options
5.1.      Bind options
5.2.      Server and default-server options

6.    HTTP header manipulation

7.    Using ACLs and pattern extraction
7.1.      Matching integers
7.2.      Matching strings
7.3.      Matching regular expressions (regexes)
7.4.      Matching IPv4 and IPv6 addresses
7.5.      Available matching criteria
7.5.1.        Matching at Layer 4 and below
7.5.2.        Matching contents at Layer 4
7.5.3.        Matching at Layer 7
7.6.      Pre-defined ACLs
7.7.      Using ACLs to form conditions
7.8.      Pattern extraction

8.    Logging
8.1.      Log levels
8.2.      Log formats
8.2.1.        Default log format
8.2.2.        TCP log format
8.2.3.        HTTP log format
8.2.4.        Custom log format
8.2.5.        Error log format
8.3.      Advanced logging options
8.3.1.        Disabling logging of external tests
8.3.2.        Logging before waiting for the session to terminate
8.3.3.        Raising log level upon errors
8.3.4.        Disabling logging of successful connections
8.4.      Timing events
8.5.      Session state at disconnection
8.6.      Non-printable characters
8.7.      Capturing HTTP cookies
8.8.      Capturing HTTP headers
8.9.      Examples of logs

9.    Statistics and monitoring
9.1.      CSV format
9.2.      Unix Socket commands


1. Quick reminder about HTTP
----------------------------

When haproxy 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.


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. Traditionally, 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.

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.

By default HAProxy operates in a tunnel-like mode with regards to persistent
connections: for each connection it processes the first request and forwards
everything else (including additional requests) to selected server. Once
established, the connection is persisted both on the client and server
sides. Use "option http-server-close" to preserve client persistent connections
while handling every incoming request individually, dispatching them one after
another to servers, in HTTP close mode. Use "option httpclose" to switch both
sides to HTTP close mode. "option forceclose" and "option
http-pretend-keepalive" help working around servers misbehaving in HTTP close
mode.


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


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.


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 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.


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

As a special case, HTTP supports so called "Informational responses" as status
codes 1xx. These messages are special in that they don't convey any part of the
response, they're just used as sort of a signaling message to ask a client to
continue to post its request for instance. In the case of a status 100 response
the requested information will be carried by the next non-100 response message
following the informational one. This implies that multiple responses may be
sent to a single request, and that this only works when keep-alive is enabled
(1xx messages are HTTP/1.1 only). HAProxy handles these messages and is able to
correctly forward and skip them, and only process the next non-100 response. As
such, these messages are neither logged nor transformed, unless explicitly
state otherwise. Status 101 messages indicate that the protocol is changing
over the same connection and that haproxy must switch to tunnel mode, just as
if a CONNECT had occurred. Then the Upgrade header would contain additional
information about the type of protocol the connection is switching to.


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 :
 - 1xx = informational message to be skipped (eg: 100, 101)
 - 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
4.2).


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 1.2.2 for more
details.


2. Configuring HAProxy
----------------------

2.1. Configuration file format
------------------------------

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
preceded by a backslash ('\') to be escaped. Backslashes also have to be
escaped by doubling them.


2.2. Time format
----------------

Some parameters involve values representing 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


2.3. Examples
-------------

    # Simple configuration for an HTTP proxy listening on port 80 on all
    # interfaces and forwarding requests to a single backend "servers" with a
    # single server "server1" listening on 127.0.0.1:8000
    global
        daemon
        maxconn 256

    defaults
        mode http
        timeout connect 5000ms
        timeout client 50000ms
        timeout server 50000ms

    frontend http-in
        bind *:80
        default_backend servers

    backend servers
        server server1 127.0.0.1:8000 maxconn 32


    # The same configuration defined with a single listen block. Shorter but
    # less expressive, especially in HTTP mode.
    global
        daemon
        maxconn 256

    defaults
        mode http
        timeout connect 5000ms
        timeout client 50000ms
        timeout server 50000ms

    listen http-in
        bind *:80
        server server1 127.0.0.1:8000 maxconn 32


Assuming haproxy is in $PATH, test these configurations in a shell with:

    $ sudo haproxy -f configuration.conf -c


3. 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
   - ca-base
   - chroot
   - crt-base
   - daemon
   - gid
   - group
   - log
   - log-send-hostname
   - nbproc
   - pidfile
   - uid
   - ulimit-n
   - user
   - stats
   - node
   - description
   - unix-bind

 * Performance tuning
   - maxconn
   - maxconnrate
   - maxcomprate
   - maxcompcpuusage
   - maxpipes
   - maxsslconn
   - noepoll
   - nokqueue
   - nopoll
   - nosplice
   - spread-checks
   - tune.bufsize
   - tune.chksize
   - tune.comp.maxlevel
   - tune.http.cookielen
   - tune.http.maxhdr
   - tune.maxaccept
   - tune.maxpollevents
   - tune.maxrewrite
   - tune.pipesize
   - tune.rcvbuf.client
   - tune.rcvbuf.server
   - tune.sndbuf.client
   - tune.sndbuf.server
   - tune.ssl.cachesize
   - tune.zlib.memlevel
   - tune.zlib.windowsize

 * Debugging
   - debug
   - quiet


3.1. Process management and security
------------------------------------

ca-base <dir>
  Assigns a default directory to fetch SSL CA certificates and CRLs from when a
  relative path is used with "ca-file" or "crl-file" directives. Absolute
  locations specified in "ca-file" and "crl-file" prevail and ignore "ca-base".

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.

cpu-map <"all"|"odd"|"even"|process_num> <cpu-set>...
  On Linux 2.6 and above, it is possible to bind a process to a specific CPU
  set. This means that the process will never run on other CPUs. The "cpu-map"
  directive specifies CPU sets for process sets. The first argument is the
  process number to bind. This process must have a number between 1 and 32,
  and any process IDs above nbproc are ignored. It is possible to specify all
  processes at once using "all", only odd numbers using "odd" or even numbers
  using "even", just like with the "bind-process" directive. The second and
  forthcoming arguments are CPU sets. Each CPU set is either a unique number
  between 0 and 31 or a range with two such numbers delimited by a dash ('-').
  Multiple CPU numbers or ranges may be specified, and the processes will be
  allowed to bind to all of them. Obviously, multiple "cpu-map" directives may
  be specified. Each "cpu-map" directive will replace the previous ones when
  they overlap.

crt-base <dir>
  Assigns a default directory to fetch SSL certificates from when a relative
  path is used with "crtfile" directives. Absolute locations specified after
  "crtfile" prevail and ignore "crt-base".

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.
  Note that if haproxy is started from a user having supplementary groups, it
  will only be able to drop these groups if started 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 [min 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).

        - An IPv6 address followed by a colon and optionally 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 maximum level is specified, only messages with a
  severity at least as important as this level will be sent. An optional minimum
  level can be specified. If it is set, logs emitted with a more severe level
  than this one will be capped to this level. This is used to avoid sending
  "emerg" messages on all terminals on some default syslog configurations.
  Eight levels are known :

          emerg  alert  crit   err    warning notice info  debug

log-send-hostname [<string>]
  Sets the hostname field in the syslog header. If optional "string" parameter
  is set the header is set to the string contents, otherwise uses the hostname
  of the system. Generally used if one is not relaying logs through an
  intermediate syslog server or for simply customizing the hostname printed in
  the logs.

log-tag <string>
  Sets the tag field in the syslog header to this string. It defaults to the
  program name as launched from the command line, which usually is "haproxy".
  Sometimes it can be useful to differentiate between multiple processes
  running on the same host.

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 bind-process [ all | odd | even | <number 1-32>[-<number 1-32>] ] ...
  Limits the stats socket to a certain set of processes numbers. By default the
  stats socket is bound to all processes, causing a warning to be emitted when
  nbproc is greater than 1 because there is no way to select the target process
  when connecting. However, by using this setting, it becomes possible to pin
  the stats socket to a specific set of processes, typically the first one. The
  warning will automatically be disabled when this setting is used, whatever
  the number of processes used.

stats socket [<address:port>|<path>] [param*]
  Binds a UNIX socket to <path> or a TCPv4/v6 address to <address:port>.
  Connections to this socket will return various statistics outputs and even
  allow some commands to be issued to change some runtime settings. Please
  consult section 9.2 "Unix Socket commands" for more details.

  All parameters supported by "bind" lines are supported, for instance to
  restrict access to some users or their access rights. Please consult
  section 5.1 for more information.

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.

unix-bind [ prefix <prefix> ] [ mode <mode> ] [ user <user> ] [ uid <uid> ]
          [ group <group> ] [ gid <gid> ]

  Fixes common settings to UNIX listening sockets declared in "bind" statements.
  This is mainly used to simplify declaration of those UNIX sockets and reduce
  the risk of errors, since those settings are most commonly required but are
  also process-specific. The <prefix> setting can be used to force all socket
  path to be relative to that directory. This might be needed to access another
  component's chroot. Note that those paths are resolved before haproxy chroots
  itself, so they are absolute. The <mode>, <user>, <uid>, <group> and <gid>
  all have the same meaning as their homonyms used by the "bind" statement. If
  both are specified, the "bind" statement has priority, meaning that the
  "unix-bind" settings may be seen as process-wide default settings.

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

node <name>
  Only letters, digits, hyphen and underscore are allowed, like in DNS names.

  This statement is useful in HA configurations where two or more processes or
  servers share the same IP address. By setting a different node-name on all
  nodes, it becomes easy to immediately spot what server is handling the
  traffic.

description <text>
  Add a text that describes the instance.

  Please note that it is required to escape certain characters (# for example)
  and this text is inserted into a html page so you should avoid using
  "<" and ">" characters.


3.2. 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".

maxconnrate <number>
  Sets the maximum per-process number of connections per second to <number>.
  Proxies will stop accepting connections when this limit is reached. It can be
  used to limit the global capacity regardless of each frontend capacity. It is
  important to note that this can only be used as a service protection measure,
  as there will not necessarily be a fair share between frontends when the
  limit is reached, so it's a good idea to also limit each frontend to some
  value close to its expected share. Also, lowering tune.maxaccept can improve
  fairness.

maxcomprate <number>
  Sets the maximum per-process input compression rate to <number> kilobytes
  pers second.  For each session, if the maximum is reached, the compression
  level will be decreased during the session. If the maximum is reached at the
  beginning of a session, the session will not compress at all. If the maximum
  is not reached, the compression level will be increased up to
  tune.comp.maxlevel.  A value of zero means there is no limit, this is the
  default value.

maxcompcpuusage <number>
  Sets the maximum CPU usage HAProxy can reach before stopping the compression
  for new requests or decreasing the compression level of current requests.
  It works like 'maxcomprate' but measures CPU usage instead of incoming data
  bandwidth. The value is expressed in percent of the CPU used by haproxy. In
  case of multiple processes (nbproc > 1), each process manages its individual
  usage. A value of 100 disable the limit. The default value is 100. Setting
  a lower value will prevent the compression work from slowing the whole
  process down and from introducing high latencies.

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.

maxsslconn <number>
  Sets the maximum per-process number of concurrent SSL connections to
  <number>. By default there is no SSL-specific limit, which means that the
  global maxconn setting will apply to all connections. Setting this limit
  avoids having openssl use too much memory and crash when malloc returns NULL
  (since it unfortunately does not reliably check for such conditions). Note
  that the limit applies both to incoming and outgoing connections, so one
  connection which is deciphered then ciphered accounts for 2 SSL connections.

maxzlibmem <number>
  Sets the maximum amount of RAM in megabytes per process usable by the zlib.
  When the maximum amount is reached, future sessions will not compress as long
  as RAM is unavailable. When sets to 0, there is no limit.
  The default value is 0. The value is available in bytes on the UNIX socket
  with "show info" on the line "MaxZlibMemUsage", the memory used by zlib is
  "ZlibMemUsage" in bytes.

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 "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 "nokqueue" and "noepoll".

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 versions 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.bufsize <number>
  Sets the buffer size to this size (in bytes). Lower values allow more
  sessions to coexist in the same amount of RAM, and higher values allow some
  applications with very large cookies to work. The default value is 16384 and
  can be changed at build time. It is strongly recommended not to change this
  from the default value, as very low values will break some services such as
  statistics, and values larger than default size will increase memory usage,
  possibly causing the system to run out of memory. At least the global maxconn
  parameter should be decreased by the same factor as this one is increased.
  If HTTP request is larger than (tune.bufsize - tune.maxrewrite), haproxy will
  return HTTP 400 (Bad Request) error. Similarly if an HTTP response is larger
  than this size, haproxy will return HTTP 502 (Bad Gateway).

tune.chksize <number>
  Sets the check buffer size to this size (in bytes). Higher values may help
  find string or regex patterns in very large pages, though doing so may imply
  more memory and CPU usage. The default value is 16384 and can be changed at
  build time. It is not recommended to change this value, but to use better
  checks whenever possible.

tune.comp.maxlevel <number>
  Sets the maximum compression level. The compression level affects CPU
  usage during compression. This value affects CPU usage during compression.
  Each session using compression initializes the compression algorithm with
  this value. The default value is 1.

tune.http.cookielen <number>
  Sets the maximum length of captured cookies. This is the maximum value that
  the "capture cookie xxx len yyy" will be allowed to take, and any upper value
  will automatically be truncated to this one. It is important not to set too
  high a value because all cookie captures still allocate this size whatever
  their configured value (they share a same pool). This value is per request
  per response, so the memory allocated is twice this value per connection.
  When not specified, the limit is set to 63 characters. It is recommended not
  to change this value.

tune.http.maxhdr <number>
  Sets the maximum number of headers in a request. When a request comes with a
  number of headers greater than this value (including the first line), it is
  rejected with a "400 Bad Request" status code. Similarly, too large responses
  are blocked with "502 Bad Gateway". The default value is 101, which is enough
  for all usages, considering that the widely deployed Apache server uses the
  same limit. It can be useful to push this limit further to temporarily allow
  a buggy application to work by the time it gets fixed. Keep in mind that each
  new header consumes 32bits of memory for each session, so don't push this
  limit too high.

tune.maxaccept <number>
  Sets the maximum number of consecutive connections a process may accept in a
  row before switching to other work. In single process mode, higher numbers
  give better performance at high connection rates. However in multi-process
  modes, keeping a bit of fairness between processes generally is better to
  increase performance. This value applies individually to each listener, so
  that the number of processes a listener is bound to is taken into account.
  This value defaults to 64. In multi-process mode, it is divided by twice
  the number of processes the listener is bound to. 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.

tune.maxrewrite <number>
  Sets the reserved buffer space to this size in bytes. The reserved space is
  used for header rewriting or appending. The first reads on sockets will never
  fill more than bufsize-maxrewrite. Historically it has defaulted to half of
  bufsize, though that does not make much sense since there are rarely large
  numbers of headers to add. Setting it too high prevents processing of large
  requests or responses. Setting it too low prevents addition of new headers
  to already large requests or to POST requests. It is generally wise to set it
  to about 1024. It is automatically readjusted to half of bufsize if it is
  larger than that. This means you don't have to worry about it when changing
  bufsize.

tune.pipesize <number>
  Sets the kernel pipe buffer size to this size (in bytes). By default, pipes
  are the default size for the system. But sometimes when using TCP splicing,
  it can improve performance to increase pipe sizes, especially if it is
  suspected that pipes are not filled and that many calls to splice() are
  performed. This has an impact on the kernel's memory footprint, so this must
  not be changed if impacts are not understood.

tune.rcvbuf.client <number>
tune.rcvbuf.server <number>
  Forces the kernel socket receive buffer size on the client or the server side
  to the specified value in bytes. This value applies to all TCP/HTTP frontends
  and backends. It should normally never be set, and the default size (0) lets
  the kernel autotune this value depending on the amount of available memory.
  However it can sometimes help to set it to very low values (eg: 4096) in
  order to save kernel memory by preventing it from buffering too large amounts
  of received data. Lower values will significantly increase CPU usage though.

tune.sndbuf.client <number>
tune.sndbuf.server <number>
  Forces the kernel socket send buffer size on the client or the server side to
  the specified value in bytes. This value applies to all TCP/HTTP frontends
  and backends. It should normally never be set, and the default size (0) lets
  the kernel autotune this value depending on the amount of available memory.
  However it can sometimes help to set it to very low values (eg: 4096) in
  order to save kernel memory by preventing it from buffering too large amounts
  of received data. Lower values will significantly increase CPU usage though.
  Another use case is to prevent write timeouts with extremely slow clients due
  to the kernel waiting for a large part of the buffer to be read before
  notifying haproxy again.

tune.ssl.cachesize <number>
  Sets the size of the global SSL session cache, in a number of blocks. A block
  is large enough to contain an encoded session without peer certificate.
  An encoded session with peer certificate is stored in multiple blocks
  depending on the size of the peer certificate. A block use approximatively
  200 bytes of memory. The default value may be forced at build time, otherwise
  defaults to 20000.  When the cache is full, the most idle entries are purged
  and reassigned. Higher values reduce the occurrence of such a purge, hence
  the number of CPU-intensive SSL handshakes by ensuring that all users keep
  their session as long as possible. All entries are pre-allocated upon startup
  and are shared between all processes if "nbproc" is greater than 1. Setting
  this value to 0 disables the SSL session cache.

tune.ssl.lifetime <timeout>
  Sets how long a cached SSL session may remain valid. This time is expressed
  in seconds and defaults to 300 (5 mn). It is important to understand that it
  does not guarantee that sessions will last that long, because if the cache is
  full, the longest idle sessions will be purged despite their configured
  lifetime. The real usefulness of this setting is to prevent sessions from
  being used for too long.

tune.zlib.memlevel <number>
  Sets the memLevel parameter in zlib initialization for each session. It
  defines how much memory should be allocated for the intenal compression
  state. A value of 1 uses minimum memory but is slow and reduces compression
  ratio, a value of 9 uses maximum memory for optimal speed.  Can be a value
  between 1 and 9. The default value is 8.

tune.zlib.windowsize <number>
  Sets the window size (the size of the history buffer) as a parameter of the
  zlib initialization for each session. Larger values of this parameter result
  in better compression at the expense of memory usage.  Can be a value between
  8 and 15.  The default value is 15.

3.3. 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".


3.4. Userlists
--------------
It is possible to control access to frontend/backend/listen sections or to
http stats by allowing only authenticated and authorized users. To do this,
it is required to create at least one userlist and to define users.

userlist <listname>
  Creates new userlist with name <listname>. Many independent userlists can be
  used to store authentication & authorization data for independent customers.

group <groupname> [users <user>,<user>,(...)]
  Adds group <groupname> to the current userlist. It is also possible to
  attach users to this group by using a comma separated list of names
  proceeded by "users" keyword.

user <username> [password|insecure-password <password>]
                [groups <group>,<group>,(...)]
  Adds user <username> to the current userlist. Both secure (encrypted) and
  insecure (unencrypted) passwords can be used. Encrypted passwords are
  evaluated using the crypt(3) function so depending of the system's
  capabilities, different algorithms are supported. For example modern Glibc
  based Linux system supports MD5, SHA-256, SHA-512 and of course classic,
  DES-based method of crypting passwords.


  Example:
        userlist L1
          group G1 users tiger,scott
          group G2 users xdb,scott

          user tiger password $6$k6y3o.eP$JlKBx9za9667qe4(...)xHSwRv6J.C0/D7cV91
          user scott insecure-password elgato
          user xdb insecure-password hello

        userlist L2
          group G1
          group G2

          user tiger password $6$k6y3o.eP$JlKBx(...)xHSwRv6J.C0/D7cV91 groups G1
          user scott insecure-password elgato groups G1,G2
          user xdb insecure-password hello groups G2

  Please note that both lists are functionally identical.


3.5. Peers
----------
It is possible to synchronize server entries in stick tables between several
haproxy instances over TCP connections in a multi-master fashion. Each instance
pushes its local updates and insertions to remote peers. Server IDs are used to
identify servers remotely, so it is important that configurations look similar
or at least that the same IDs are forced on each server on all participants.
Interrupted exchanges are automatically detected and recovered from the last
known point. In addition, during a soft restart, the old process connects to
the new one using such a TCP connection to push all its entries before the new
process tries to connect to other peers. That ensures very fast replication
during a reload, it typically takes a fraction of a second even for large
tables.

peers <peersect>
  Creates a new peer list with name <peersect>. It is an independent section,
  which is referenced by one or more stick-tables.

peer <peername> <ip>:<port>
  Defines a peer inside a peers section.
  If <peername> is set to the local peer name (by default hostname, or forced
  using "-L" command line option), haproxy will listen for incoming remote peer
  connection on <ip>:<port>. Otherwise, <ip>:<port> defines where to connect to
  to join the remote peer, and <peername> is used at the protocol level to
  identify and validate the remote peer on the server side.

  During a soft restart, local peer <ip>:<port> is used by the old instance to
  connect the new one and initiate a complete replication (teaching process).

  It is strongly recommended to have the exact same peers declaration on all
  peers and to only rely on the "-L" command line argument to change the local
  peer name. This makes it easier to maintain coherent configuration files
  across all peers.

  Example:
    peers mypeers
        peer haproxy1 192.168.0.1:1024
        peer haproxy2 192.168.0.2:1024
        peer haproxy3 10.2.0.1:1024

    backend mybackend
        mode tcp
        balance roundrobin
        stick-table type ip size 20k peers mypeers
        stick on src

        server srv1 192.168.0.30:80
        server srv2 192.168.0.31:80


4. 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
bidirectional 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.


4.1. 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
marked with "(*)" can be optionally inverted using the "no" prefix, eg. "no
option contstats". This makes sense when the option has been enabled by default
and must be disabled for a specific instance. Such options may also be prefixed
with "default" in order to restore default settings regardless of what has been
specified in a previous "defaults" section.


 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                  (deprecated)  X          X         X         -
compression                               X          X         X         X
contimeout                  (deprecated)  X          -         X         X
cookie                                    X          -         X         X
default-server                            X          -         X         X
default_backend                           X          X         X         -
description                               -          X         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
-- keyword -------------------------- defaults - frontend - listen -- backend -
errorloc303                               X          X         X         X
force-persist                             -          X         X         X
fullconn                                  X          -         X         X
grace                                     X          X         X         X
hash-type                                 X          -         X         X
http-check disable-on-404                 X          -         X         X
http-check expect                         -          -         X         X
http-check send-state                     X          -         X         X
http-request                              -          X         X         X
id                                        -          X         X         X
ignore-persist                            -          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         -
option abortonclose                  (*)  X          -         X         X
option accept-invalid-http-request   (*)  X          X         X         -
option accept-invalid-http-response  (*)  X          -         X         X
option allbackups                    (*)  X          -         X         X
option checkcache                    (*)  X          -         X         X
option clitcpka                      (*)  X          X         X         -
option contstats                     (*)  X          X         X         -
option dontlog-normal                (*)  X          X         X         -
option dontlognull                   (*)  X          X         X         -
option forceclose                    (*)  X          X         X         X
-- keyword -------------------------- defaults - frontend - listen -- backend -
option forwardfor                         X          X         X         X
option http-no-delay                 (*)  X          X         X         X
option http-pretend-keepalive        (*)  X          X         X         X
option http-server-close             (*)  X          X         X         X
option http-use-proxy-header         (*)  X          X         X         -
option httpchk                            X          -         X         X
option httpclose                     (*)  X          X         X         X
option httplog                            X          X         X         X
option http_proxy                    (*)  X          X         X         X
option independent-streams           (*)  X          X         X         X
option ldap-check                         X          -         X         X
option log-health-checks             (*)  X          -         X         X
option log-separate-errors           (*)  X          X         X         -
option logasap                       (*)  X          X         X         -
option mysql-check                        X          -         X         X
option pgsql-check                        X          -         X         X
option nolinger                      (*)  X          X         X         X
option originalto                         X          X         X         X
option persist                       (*)  X          -         X         X
option redispatch                    (*)  X          -         X         X
option redis-check                        X          -         X         X
option smtpchk                            X          -         X         X
option socket-stats                  (*)  X          X         X         -
option splice-auto                   (*)  X          X         X         X
option splice-request                (*)  X          X         X         X
option splice-response               (*)  X          X         X         X
option srvtcpka                      (*)  X          -         X         X
option ssl-hello-chk                      X          -         X         X
-- keyword -------------------------- defaults - frontend - listen -- backend -
option tcp-smart-accept              (*)  X          X         X         -
option tcp-smart-connect             (*)  X          -         X         X
option tcpka                              X          X         X         X
option tcplog                             X          X         X         X
option transparent                   (*)  X          -         X         X
persist rdp-cookie                        X          -         X         X
rate-limit sessions                       X          X         X         -
redirect                                  -          X         X         X
redisp                      (deprecated)  X          -         X         X
redispatch                  (deprecated)  X          -         X         X
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
-- keyword -------------------------- defaults - frontend - listen -- backend -
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                  (deprecated)  X          -         X         X
stats admin                               -          -         X         X
stats auth                                X          -         X         X
stats enable                              X          -         X         X
stats hide-version                        X          -         X         X
stats http-request                        -          -         X         X
stats realm                               X          -         X         X
stats refresh                             X          -         X         X
stats scope                               X          -         X         X
stats show-desc                           X          -         X         X
stats show-legends                        X          -         X         X
stats show-node                           X          -         X         X
stats uri                                 X          -         X         X
-- keyword -------------------------- defaults - frontend - listen -- backend -
stick match                               -          -         X         X
stick on                                  -          -         X         X
stick store-request                       -          -         X         X
stick store-response                      -          -         X         X
stick-table                               -          -         X         X
tcp-request connection                    -          X         X         -
tcp-request content                       -          X         X         X
tcp-request inspect-delay                 -          X         X         X
tcp-response content                      -          -         X         X
tcp-response inspect-delay                -          -         X         X
timeout check                             X          -         X         X
timeout client                            X          X         X         -
timeout clitimeout          (deprecated)  X          X         X         -
timeout connect                           X          -         X         X
timeout contimeout          (deprecated)  X          -         X         X
timeout http-keep-alive                   X          X         X         X
timeout http-request                      X          X         X         X
timeout queue                             X          -         X         X
timeout server                            X          -         X         X
timeout srvtimeout          (deprecated)  X          -         X         X
timeout tarpit                            X          X         X         X
timeout tunnel                            X          -         X         X
transparent                 (deprecated)  X          -         X         X
unique-id-format                          X          X         X         -
unique-id-header                          X          X         X         -
use_backend                               -          X         X         -
use-server                                -          -         X         X
------------------------------------+----------+----------+---------+---------
 keyword                              defaults   frontend   listen    backend


4.2. 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 7 about ACL usage.


appsession <cookie> len <length> timeout <holdtime>
           [request-learn] [prefix] [mode <path-parameters|query-string>]
  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 max 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.

    request-learn
               If this option is specified, then haproxy will be able to learn
               the cookie found in the request in case the server does not
               specify any in response. This is typically what happens with
               PHPSESSID cookies, or when haproxy's session expires before
               the application's session and the correct server is selected.
               It is recommended to specify this option to improve reliability.

    prefix     When this option is specified, haproxy will match on the cookie
               prefix (or URL parameter prefix). The appsession value is the
               data following this prefix.

               Example :
               appsession ASPSESSIONID len 64 timeout 3h prefix

               This will match the cookie ASPSESSIONIDXXXX=XXXXX,
               the appsession value will be XXXX=XXXXX.

    mode       This option allows to change the URL parser mode.
               2 modes are currently supported :
               - path-parameters :
                 The parser looks for the appsession in the path parameters
                 part (each parameter is separated by a semi-colon), which is
                 convenient for JSESSIONID for example.
                 This is the default mode if the option is not set.
               - query-string :
                 In this mode, the parser will look for the appsession in the
                 query string.

  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 (depending on
  the mode used). 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.

  Note : Consider not using this feature in multi-process mode (nbproc > 1)
         unless you know what you do : memory is not shared between the
         processes, which can result in random behaviours.

  Example :
        appsession JSESSIONID len 52 timeout 3h

  See also : "cookie", "capture cookie", "balance", "stick", "stick-table",
             "ignore-persist", "nbproc" and "bind-process".


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. It is limited by
                  design to 4128 active servers per backend. Note that in some
                  large farms, when a server becomes up after having been down
                  for a very short time, it may sometimes take a few hundreds
                  requests for it to be re-integrated into the farm and start
                  receiving traffic. This is normal, though very rare. It is
                  indicated here in case you would have the chance to observe
                  it, so that you don't worry.

      static-rr   Each server is used in turns, according to their weights.
                  This algorithm is as similar to roundrobin except that it is
                  static, which means that changing a server's weight on the
                  fly will have no effect. On the other hand, it has no design
                  limitation on the number of servers, and when a server goes
                  up, it is always immediately reintroduced into the farm, once
                  the full map is recomputed. It also uses slightly less CPU to
                  run (around -1%).

      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.

      first       The first server with available connection slots receives the
                  connection. The servers are choosen from the lowest numeric
                  identifier to the highest (see server parameter "id"), which
                  defaults to the server's position in the farm. Once a server
                  reaches its maxconn value, the next server is used. It does
                  not make sense to use this algorithm without setting maxconn.
                  The purpose of this algorithm is to always use the smallest
                  number of servers so that extra servers can be powered off
                  during non-intensive hours. This algorithm ignores the server
                  weight, and brings more benefit to long session such as RDP
                  or IMAP than HTTP, though it can be useful there too. In
                  order to use this algorithm efficiently, it is recommended
                  that a cloud controller regularly checks server usage to turn
                  them off when unused, and regularly checks backend queue to
                  turn new servers on when the queue inflates. Alternatively,
                  using "http-check send-state" may inform servers on the load.

      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 stickiness
                  to clients which refuse session cookies. This algorithm is
                  static by default, which means that changing a server's
                  weight on the fly will have no effect, but this can be
                  changed using "hash-type".

      uri         This algorithm hashes either the left part of the URI (before
                  the question mark) or the whole URI (if the "whole" parameter
                  is present) and divides the hash value by the total weight of
                  the running servers. The result designates which server will
                  receive the request. This ensures that the 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 by default, which means that
                  changing a server's weight on the fly will have no effect,
                  but this can be changed using "hash-type".

                  This algorithm supports 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 it is not found in a query string after a question mark
                  ('?') 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 by default, which means
                  that changing a server's weight on the fly will have no
                  effect, but this can be changed using "hash-type".

      hdr(<name>) The HTTP header <name> will be looked up in each HTTP
                  request. Just as with the equivalent ACL 'hdr()' function,
                  the header name in parenthesis is not case sensitive. If the
                  header is absent or if it does not contain any value, the
                  roundrobin algorithm is applied instead.

                  An optional 'use_domain_only' parameter is available, for
                  reducing the hash algorithm to the main domain part with some
                  specific headers such as 'Host'. For instance, in the Host
                  value "haproxy.1wt.eu", only "1wt" will be considered.

                  This algorithm is static by default, which means that
                  changing a server's weight on the fly will have no effect,
                  but this can be changed using "hash-type".

      rdp-cookie
      rdp-cookie(<name>)
                  The RDP cookie <name> (or "mstshash" if omitted) will be
                  looked up and hashed for each incoming TCP request. Just as
                  with the equivalent ACL 'req_rdp_cookie()' function, the name
                  is not case-sensitive. This mechanism is useful as a degraded
                  persistence mode, as it makes it possible to always send the
                  same user (or the same session ID) to the same server. If the
                  cookie is not found, the normal roundrobin algorithm is
                  used instead.

                  Note that for this to work, the frontend must ensure that an
                  RDP cookie is already present in the request buffer. For this
                  you must use 'tcp-request content accept' rule combined with
                  a 'req_rdp_cookie_cnt' ACL.

                  This algorithm is static by default, which means that
                  changing a server's weight on the fly will have no effect,
                  but this can be changed using "hash-type".

                  See also the rdp_cookie pattern fetch function.

    <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
        balance hdr(User-Agent)
        balance hdr(host)
        balance hdr(Host) use_domain_only

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

    - all POST requests are eligible 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. Scanning 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", "hash-type" and
             "http_proxy".


bind [<address>]:<port_range> [, ...] [param*]
bind /<path> [, ...] [param*]
  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". The IPv6 equivalent is '::'.

    <port_range>  is either a unique TCP port, or a port range for which the
                  proxy will accept connections for the IP address specified
                  above. The port is mandatory for TCP listeners. Note that in
                  the case of an IPv6 address, the port is always the number
                  after the last colon (':'). A range can either be :
                   - a numerical port (ex: '80')
                   - a dash-delimited ports range explicitly stating the lower
                     and upper bounds (ex: '2000-2100') which are included in
                     the range.

                  Particular care must be taken against port ranges, because
                  every <address:port> couple consumes one socket (= a file
                  descriptor), so it's easy to consume lots of descriptors
                  with a simple range, and to run out of sockets. Also, each
                  <address:port> couple must be used only once among all
                  instances running on a same system. Please note that binding
                  to ports lower than 1024 generally require particular
                  privileges to start the program, which are independent of
                  the 'uid' parameter.

    <path>        is a UNIX socket path beginning with a slash ('/'). This is
                  alternative to the TCP listening port. Haproxy will then
                  receive UNIX connections on the socket located at this place.
                  The path must begin with a slash and by default is absolute.
                  It can be relative to the prefix defined by "unix-bind" in
                  the global section. Note that the total length of the prefix
                  followed by the socket path cannot exceed some system limits
                  for UNIX sockets, which commonly are set to 107 characters.

    <param*>      is a list of parameters common to all sockets declared on the
                  same line. These numerous parameters depend on OS and build
                  options and have a complete section dedicated to them. Please
                  refer to section 5 to for more details.

  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
            bind /var/run/ssl-frontend.sock user root mode 600 accept-proxy

        listen http_https_proxy
            bind :80
            bind :443 ssl crt /etc/haproxy/site.pem

  See also : "source", "option forwardfor", "unix-bind" and the PROXY protocol
             documentation, and section 5 about bind options.


bind-process [ all | odd | even | <number 1-32>[-<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 or range,
                  whose values must all be 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

        listen management
            bind 10.0.0.4:80
            bind-process 1-4

  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 7). This is
  typically used to deny access to certain sensitive 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 7 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 set
  by the global "tune.http.cookielen" setting and defaults to 63 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 8 about logging.


capture request header <name> len <length>
  Capture and log the last 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>.

  The complete 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
  differentiate 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 nor to their
  length, though it is wise to keep them low to limit memory usage per session.
  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 8
             about logging.


capture response header <name> len <length>
  Capture and log the last 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>.

  The complete 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 nor to their
  length, though it is wise to keep them low to limit memory usage per session.
  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 8
             about logging.


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 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".

compression algo <algorithm> ...
compression type <mime type> ...
compression offload
  Enable HTTP compression.
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    yes   |   yes  |   yes
  Arguments :
    algo     is followed by the list of supported compression algorithms.
    type     is followed by the list of MIME types that will be compressed.
    offload  makes haproxy work as a compression offloader only (see notes).

  The currently supported algorithms are :
    identity  this is mostly for debugging, and it was useful for developing
              the compression feature. Identity does not apply any change on
              data.

    gzip      applies gzip compression. This setting is only available when
              support for zlib was built in.

    deflate   same as gzip, but with deflate algorithm and zlib format.
              Note that this algorithm has ambiguous support on many browsers
              and no support at all from recent ones. It is strongly
              recommended not to use it for anything else than experimentation.
              This setting is only available when support for zlib was built
              in.

  Compression will be activated depending on the Accept-Encoding request
  header. With identity, it does not take care of that header.
  If backend servers support HTTP compression, these directives
  will be no-op: haproxy will see the compressed response and will not
  compress again. If backend servers do not support HTTP compression and
  there is Accept-Encoding header in request, haproxy will compress the
  matching response.

  The "offload" setting makes haproxy remove the Accept-Encoding header to
  prevent backend servers from compressing responses. It is strongly
  recommended not to do this because this means that all the compression work
  will be done on the single point where haproxy is located. However in some
  deployment scenarios, haproxy may be installed in front of a buggy gateway
  with broken HTTP compression implementation which can't be turned off.
  In that case haproxy can be used to prevent that gateway from emitting
  invalid payloads. In this case, simply removing the header in the
  configuration does not work because it applies before the header is parsed,
  so that prevents haproxy from compressing. The "offload" setting should
  then be used for such scenarios.

  Compression is disabled when:
    * the request does not advertise a supported compression algorithm in the
      "Accept-Encoding" header
    * the response message is not HTTP/1.1
    * HTTP status code is not 200
    * response contain neither a "Content-Length" header nor a
      "Transfer-Encoding" whose last value is "chunked"
    * response contains a "Content-Type" header whose first value starts with
      "multipart"
    * the response contains the "no-transform" value in the "Cache-control"
      header
    * User-Agent matches "Mozilla/4" unless it is MSIE 6 with XP SP2, or MSIE 7
      and later
    * The response contains a "Content-Encoding" header, indicating that the
      response is already compressed (see compression offload)

  Note: The compression does not rewrite Etag headers, and does not emit the
        Warning header.

  Examples :
        compression algo gzip
        compression type text/html text/plain

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 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 ] [ preserve ] [ httponly ] [ secure ]
              [ domain <domain> ]* [ maxidle <idle> ] [ maxlife <life> ]
  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 server responses if the client did not

              already have a cookie that would have permitted it to access this
              server. When used without the "preserve" option, if the server
              emits a cookie with the same name, it will be remove before
              processing.  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. By default, unless the "indirect" option is added,
              the server will see the cookies emitted by the client. Due to
              caching effects, it is generally wise to add the "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". Note: it is highly
              recommended not to use "indirect" with "prefix", otherwise server
              cookie updates would not be sent to clients.

    indirect  When this option is specified, no cookie will be emitted to a
              client which already has a valid one for the server which has
              processed the request. If the server sets such a cookie itself,
              it will be removed, unless the "preserve" option is also set. In
              "insert" mode, this will additionally remove cookies from the
              requests transmitted to the server, making the persistence
              mechanism totally transparent from an application point of view.
              Note: it is highly recommended not to use "indirect" with
              "prefix", otherwise server cookie updates would not be sent to
              clients.

    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.

    preserve  This option may only be used with "insert" and/or "indirect". It
              allows the server to emit the persistence cookie itself. In this
              case, if a cookie is found in the response, haproxy will leave it
              untouched. This is useful in order to end persistence after a
              logout request for instance. For this, the server just has to
              emit a cookie with an invalid value (eg: empty) or with a date in
              the past. By combining this mechanism with the "disable-on-404"
              check option, it is possible to perform a completely graceful
              shutdown because users will definitely leave the server after
              they logout.

    httponly  This option tells haproxy to add an "HttpOnly" cookie attribute
              when a cookie is inserted. This attribute is used so that a
              user agent doesn't share the cookie with non-HTTP components.
              Please check RFC6265 for more information on this attribute.

    secure    This option tells haproxy to add a "Secure" cookie attribute when
              a cookie is inserted. This attribute is used so that a user agent
              never emits this cookie over non-secure channels, which means
              that a cookie learned with this flag will be presented only over
              SSL/TLS connections. Please check RFC6265 for more information on
              this attribute.

    domain    This option allows to specify the domain at which a cookie is
              inserted. It requires exactly one parameter: a valid domain
              name. If the domain begins with a dot, the browser is allowed to
              use it for any host ending with that name. It is also possible to
              specify several domain names by invoking this option multiple
              times. Some browsers might have small limits on the number of
              domains, so be careful when doing that. For the record, sending
              10 domains to MSIE 6 or Firefox 2 works as expected.

    maxidle   This option allows inserted cookies to be ignored after some idle
              time. It only works with insert-mode cookies. When a cookie is
              sent to the client, the date this cookie was emitted is sent too.
              Upon further presentations of this cookie, if the date is older
              than the delay indicated by the parameter (in seconds), it will
              be ignored. Otherwise, it will be refreshed if needed when the
              response is sent to the client. This is particularly useful to
              prevent users who never close their browsers from remaining for
              too long on the same server (eg: after a farm size change). When
              this option is set and a cookie has no date, it is always
              accepted, but gets refreshed in the response. This maintains the
              ability for admins to access their sites. Cookies that have a
              date in the future further than 24 hours are ignored. Doing so
              lets admins fix timezone issues without risking kicking users off
              the site.

    maxlife   This option allows inserted cookies to be ignored after some life
              time, whether they're in use or not. It only works with insert
              mode cookies. When a cookie is first sent to the client, the date
              this cookie was emitted is sent too. Upon further presentations
              of this cookie, if the date is older than the delay indicated by
              the parameter (in seconds), it will be ignored. If the cookie in
              the request has no date, it is accepted and a date will be set.
              Cookies that have a date in the future further than 24 hours are
              ignored. Doing so lets admins fix timezone issues without risking
              kicking users off the site. Contrary to maxidle, this value is
              not refreshed, only the first visit date counts. Both maxidle and
              maxlife may be used at the time. This is particularly useful to
              prevent users who never close their browsers from remaining for
              too long on the same server (eg: after a farm size change). This
              is stronger than the maxidle method in that it forces a
              redispatch after some absolute delay.

  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
        cookie SRV insert indirect nocache maxidle 30m maxlife 8h

  See also : "appsession", "balance source", "capture cookie", "server"
             and "ignore-persist".


default-server [param*]
  Change default options for a server in a backend
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments:
    <param*>  is a list of parameters for this server. The "default-server"
              keyword accepts an important number of options and has a complete
              section dedicated to it. Please refer to section 5 for more
              details.

  Example :
        default-server inter 1000 weight 13

  See also: "server" and section 5 about server options


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.

  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"


dispatch <address>:<port>
  Set a default server address
  May be used in sections :   defaults | frontend | listen | backend
                                 no    |    no    |   yes  |   yes
  Arguments :

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

    <ports>   is a mandatory port specification. All connections will be sent
              to this port, and it is not permitted to use port offsets as is
              possible with normal servers.

  The "dispatch" keyword designates a default server for use when no other
  server can take the connection. In the past it was used to forward non
  persistent connections to an auxiliary load balancer. Due to its simple
  syntax, it has also been used for simple TCP relays. It is recommended not to
  use it for more clarity, and to use the "server" directive instead.

  See also : "server"


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 200, 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.

  Code 200 is emitted in response to requests matching a "monitor-uri" rule.

  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 200, 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.

  Code 200 is emitted in response to requests matching a "monitor-uri" rule.

  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.

  Code 200 is emitted in response to requests matching a "monitor-uri" rule.

  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"


force-persist { if | unless } <condition>
  Declare a condition to force persistence on down servers
  May be used in sections:    defaults | frontend | listen | backend
                                  no   |    yes   |   yes  |   yes

  By default, requests are not dispatched to down servers. It is possible to
  force this using "option persist", but it is unconditional and redispatches
  to a valid server if "option redispatch" is set. That leaves with very little
  possibilities to force some requests to reach a server which is artificially
  marked down for maintenance operations.

  The "force-persist" statement allows one to declare various ACL-based
  conditions which, when met, will cause a request to ignore the down status of
  a server and still try to connect to it. That makes it possible to start a
  server, still replying an error to the health checks, and run a specially
  configured browser to test the service. Among the handy methods, one could
  use a specific source IP address, or a specific cookie. The cookie also has
  the advantage that it can easily be added/removed on the browser from a test
  page. Once the service is validated, it is then possible to open the service
  to the world by returning a valid response to health checks.

  The forced persistence is enabled when an "if" condition is met, or unless an
  "unless" condition is met. The final redispatch is always disabled when this
  is used.

  See also : "option redispatch", "ignore-persist", "persist",
             and section 7 about ACL usage.


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
  exceptional loads.

  Since it's hard to get this value right, haproxy automatically sets it to
  10% of the sum of the maxconns of all frontends that may branch to this
  backend. That way it's safe to leave it unset.

  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
                                 yes   |    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 equipment 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.


hash-type <method>
  Specify a method to use for mapping hashes to servers
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments :
    map-based   the hash table is a static array containing all alive servers.
                The hashes will be very smooth, will consider weights, but will
                be static in that weight changes while a server is up will be
                ignored. This means that there will be no slow start. Also,
                since a server is selected by its position in the array, most
                mappings are changed when the server count changes. This means
                that when a server goes up or down, or when a server is added
                to a farm, most connections will be redistributed to different
                servers. This can be inconvenient with caches for instance.

    avalanche   this mechanism uses the default map-based hashing described
                above but applies a full avalanche hash before performing the
                mapping. The result is a slightly less smooth hash for most
                situations, but the hash becomes better than pure map-based
                hashes when the number of servers is a multiple of the size of
                the input set. When using URI hash with a number of servers
                multiple of 64, it's desirable to change the hash type to
                this value.

    consistent  the hash table is a tree filled with many occurrences of each
                server. The hash key is looked up in the tree and the closest
                server is chosen. This hash is dynamic, it supports changing
                weights while the servers are up, so it is compatible with the
                slow start feature. It has the advantage that when a server
                goes up or down, only its associations are moved. When a server
                is added to the farm, only a few part of the mappings are
                redistributed, making it an ideal algorithm for caches.
                However, due to its principle, the algorithm will never be very
                smooth and it may sometimes be necessary to adjust a server's
                weight or its ID to get a more balanced distribution. In order
                to get the same distribution on multiple load balancers, it is
                important that all servers have the same IDs.

  The default hash type is "map-based" and is recommended for most usages.

  See also : "balance", "server"


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. If this option
  is used with "http-check expect", then it has precedence over it so that 404
  responses will still be considered as soft-stop.

  See also : "option httpchk", "http-check expect"


http-check expect [!] <match> <pattern>
  Make HTTP health checks consider response contents or specific status codes
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments :
    <match>   is a keyword indicating how to look for a specific pattern in the
              response. The keyword may be one of "status", "rstatus",
              "string", or "rstring". The keyword may be preceded by an
              exclamation mark ("!") to negate the match. Spaces are allowed
              between the exclamation mark and the keyword. See below for more
              details on the supported keywords.

    <pattern> is the pattern to look for. It may be a string or a regular
              expression. If the pattern contains spaces, they must be escaped
              with the usual backslash ('\').

  By default, "option httpchk" considers that response statuses 2xx and 3xx
  are valid, and that others are invalid. When "http-check expect" is used,
  it defines what is considered valid or invalid. Only one "http-check"
  statement is supported in a backend. If a server fails to respond or times
  out, the check obviously fails. The available matches are :

    status <string> : test the exact string match for the HTTP status code.
                      A health check response will be considered valid if the
                      response's status code is exactly this string. If the
                      "status" keyword is prefixed with "!", then the response
                      will be considered invalid if the status code matches.

    rstatus <regex> : test a regular expression for the HTTP status code.
                      A health check response will be considered valid if the
                      response's status code matches the expression. If the
                      "rstatus" keyword is prefixed with "!", then the response
                      will be considered invalid if the status code matches.
                      This is mostly used to check for multiple codes.

    string <string> : test the exact string match in the HTTP response body.
                      A health check response will be considered valid if the
                      response's body contains this exact string. If the
                      "string" keyword is prefixed with "!", then the response
                      will be considered invalid if the body contains this
                      string. This can be used to look for a mandatory word at
                      the end of a dynamic page, or to detect a failure when a
                      specific error appears on the check page (eg: a stack
                      trace).

    rstring <regex> : test a regular expression on the HTTP response body.
                      A health check response will be considered valid if the
                      response's body matches this expression. If the "rstring"
                      keyword is prefixed with "!", then the response will be
                      considered invalid if the body matches the expression.
                      This can be used to look for a mandatory word at the end
                      of a dynamic page, or to detect a failure when a specific
                      error appears on the check page (eg: a stack trace).

  It is important to note that the responses will be limited to a certain size
  defined by the global "tune.chksize" option, which defaults to 16384 bytes.
  Thus, too large responses may not contain the mandatory pattern when using
  "string" or "rstring". If a large response is absolutely required, it is
  possible to change the default max size by setting the global variable.
  However, it is worth keeping in mind that parsing very large responses can
  waste some CPU cycles, especially when regular expressions are used, and that
  it is always better to focus the checks on smaller resources.

  Last, if "http-check expect" is combined with "http-check disable-on-404",
  then this last one has precedence when the server responds with 404.

  Examples :
         # only accept status 200 as valid
         http-check expect status 200

         # consider SQL errors as errors
         http-check expect ! string SQL\ Error

         # consider status 5xx only as errors
         http-check expect ! rstatus ^5

         # check that we have a correct hexadecimal tag before /html
         http-check expect rstring <!--tag:[0-9a-f]*</html>

  See also : "option httpchk", "http-check disable-on-404"


http-check send-state
  Enable emission of a state header with HTTP health checks
  May be used in sections :   defaults | frontend | listen | backend
                                 yes   |    no    |   yes  |   yes
  Arguments : none

  When this option is set, haproxy will systematically send a special header
  "X-Haproxy-Server-State" with a list of parameters indicating to each server
  how they are seen by haproxy. This can be used for instance when a server is
  manipulated without access to haproxy and the operator needs to know whether
  haproxy still sees it up or not, or if the server is the last one in a farm.

  The header is composed of fields delimited by semi-colons, the first of which
  is a word ("UP", "DOWN", "NOLB"), possibly followed by a number of valid
  checks on the total number before transition, just as appears in the stats
  interface. Next headers are in the form "<variable>=<value>", indicating in
  no specific order some values available in the stats interface :
    - a variable "name", containing the name of the backend followed by a slash
      ("/") then the name of the server. This can be used when a server is
      checked in multiple backends.

    - a variable "node" containing the name of the haproxy node, as set in the
      global "node" variable, otherwise the system's hostname if unspecified.

    - a variable "weight" indicating the weight of the server, a slash ("/")
      and the total weight of the farm (just counting usable servers). This
      helps to know if other servers are available to handle the load when this
      one fails.

    - a variable "scur" indicating the current number of concurrent connections
      on the server, followed by a slash ("/") then the total number of
      connections on all servers of the same backend.

    - a variable "qcur" indicating the current number of requests in the
      server's queue.

  Example of a header received by the application server :
    >>>  X-Haproxy-Server-State: UP 2/3; name=bck/srv2; node=lb1; weight=1/2; \
           scur=13/22; qcur=0

  See also : "option httpchk", "http-check disable-on-404"

http-request { allow | deny | tarpit | auth [realm <realm>] | redirect <rule> |
              add-header <name> <fmt> | set-header <name> <fmt> }
             [ { if | unless } <condition> ]
  Access control for Layer 7 requests

  May be used in sections:   defaults | frontend | listen | backend