tree ef6b2166a4849815772693919b70f9b34b085549
parent 5564555b868ec23e00f6e6e954ce244154765ef6
author Willy Tarreau <w@1wt.eu> 1430487473 +0200
committer Willy Tarreau <w@1wt.eu> 1430487677 +0200
encoding latin1

MEDIUM: http: add option-ignore-probes to get rid of the floods of 408

Recently some browsers started to implement a "pre-connect" feature
consisting in speculatively connecting to some recently visited web sites
just in case the user would like to visit them. This results in many
connections being established to web sites, which end up in 408 Request
Timeout if the timeout strikes first, or 400 Bad Request when the browser
decides to close them first. These ones pollute the log and feed the error
counters. There was already "option dontlognull" but it's insufficient in
this case. Instead, this option does the following things :
   - prevent any 400/408 message from being sent to the client if nothing
     was received over a connection before it was closed ;
   - prevent any log from being emitted in this situation ;
   - prevent any error counter from being incremented

That way the empty connection is silently ignored. Note that it is better
not to use this unless it is clear that it is needed, because it will hide
real problems. The most common reason for not receiving a request and seeing
a 408 is due to an MTU inconsistency between the client and an intermediary
element such as a VPN, which blocks too large packets. These issues are
generally seen with POST requests as well as GET with large cookies. The logs
are often the only way to detect them.

This patch should be backported to 1.5 since it avoids false alerts and
makes it easier to monitor haproxy's status.
(cherry picked from commit 0f228a037a3565c83309dc9c0e2e546f94c17e8a)