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From Prigge Scott <>
Subject [users@httpd] TCP SYN behavior and reverse proxy (mod_proxy)
Date Wed, 11 Nov 2009 17:43:47 GMT
Hi. I'm running 2.2.8 on Linux with mod_proxy in a reverse proxy configuration, which is forwarding
data to an application server. And there is a feature within this application which relies
on HTTP POST data from the browser. We also have a third-party authentication module which
is loaded as a shared object. When the authentication shared object not loaded in Apache,
the HTTP POST data is spooled to the application server as it is being received. But when
the auth shared object is loaded, the HTTP POST data is held until all of it is received from
the browser. 

I can see in network traces that in both cases, Apache opens a new TCP connection with the
application server immediately after the initial TCP connection with the browser is established.
But over slow WAN connections for example, it takes a number of minutes to receive all of
the POST data. And since Apache initiates a new TCP connection with the app server immediately,
the TCP connection with the app server remains idle for a number of minutes. When Apache eventually
does receive all of the POST data and begins forwarding it to the application server, the
OS on the app server has timed out the TCP connection and responds with TCP RST packets. As
a result, the browser receives a "502 Bad Gateway" response.

Is there a way I might force Apache or (mod_proxy) to wait until all of the HTTP POST data
is received before establishing a new TCP connection with the app server? I have tried adding
a number of Apache/mod_proxy/mod_proxy_http directives in various combinations, but haven't
been able to change this specific behavior.

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