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From bugzi...@apache.org
Subject DO NOT REPLY [Bug 44592] mod_proxy fails to send post request to backend server
Date Mon, 30 Jun 2008 19:38:59 GMT
https://issues.apache.org/bugzilla/show_bug.cgi?id=44592


Spil <apache.org@bachfreund.nl> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEEDINFO                    |ASSIGNED




--- Comment #17 from Spil <apache.org@bachfreund.nl>  2008-06-30 12:38:58 PST ---
It seems I have a problem with the Keep-Alive in conjunction with a changing
order in sending and receiving of the TCP/IP frames.

We noticed that the last successful request from the client (as captured on the
client) near to exactly 5 seconds before the first part of the next POST was
sent by the client. Neither KeepAlive nor KeepAliveTimeout were set on Apache
leaving it default 'on' and 5 seconds.

(numbering of frame differs from previous post in this bugreport)
Trace on client
30 10:05:39.241734 S->C HTTP/1.1 200 OK [PSH,ACK]
31 10:05:39.390101 C->S [ACK]
32 10:05:44.269173 C->S First frame of POST
33 10:05:44.269313 C->S First frame of POST
34 10:05:44.275964 S->C [FIN,ACK]

Trace on proxy (clocks NOT synchronized, frame matching on Seq en Ack in tcp)
1800 11:05:55.007933 S->C SSL Continuation (client trace frame 30)
1801 11:05:55.010493 C->S ACK
1802 11:05:55.013463 C->S ACK
1803 11:05:55.163385 C->S ACK
1804 10:05:59.981127 [FIN,ACK] (client trace frame 34)
1805 10:06:00.048579 SSL Unreassembled packet (client trace frame 32)
1807 10:06:00.049030 Continuation (client trace frame 33)

Due to the latency of the network the sending and receiving order on client and
server-side have switched around.
My workaround was to set a specific KeepAliveTimeout in the Virtual Hosts
affected (37 seconds) on the productive instance. After 2 hours I had 2 more
errors:
- one where the previous request from the client was around 37 seconds before
the failing POST request
- the other had 2 requests in short succesion from which the last one failed
and the request before that was around 37 seconds earlier

The default Keep-Alive Time-Out of the Internet Explorer clients is 60 seconds
(source http://support.microsoft.com/kb/813827). I am now switching the
KeepAliveTimeout on the Apache servers to 67 seconds so it is longer than the
Keep-Alive timeout on the client.

Additionally I found my bug described in
http://support.microsoft.com/kb/921090, the PSH,ACK and FIN,ACK are listed in
the client trace. I am told that wininet.dll builds after the one mentioned in
this article can implement the fix by applying the registry setting
FEATURE_HANDLE_SSL_CLOSE_NOTIFY_KB921090 from the MSKB article. Hopefully I can
have this fix rolled out through the landscape (thousands of PC's) but that
still won't fix issues with clients not under our control.

Some questions remain open
- What are the downsides of increasing the KeepAliveTimeout > 12 times?
- Is apache behaving as should be expected?


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