Symptoms
Users will occasionally receive an error page reporting a "Bad gateway" condition, which translates to "httpd couldn't get a response from the application server."
Cause
This can result from a known issue in Apache, affecting versions 2.0.63 through to 2.2.3, and was marked as resolved with 2.2.4.
Httpd wasn't checking for one of the possible conditions for its connections to the application server, so would periodically (e.g. once in tens of thousands of requests) use a connection handle that had been reset by the appserver.
Resolution
Upgrade to the latest version of httpd (2.2.13 as at 14.08.2009).
If you're using a webserver compiled from source and have a strong reason not to upgrade, you also have the option of making a tiny edit to the source as described in one of the comments and recompiling.
Additional information
Severity: Low
Article ID: CONFKB200212803