currently RHEL 5 includes httpd 2.2.3 which does not include the BALANCER_* environment variables that were addid in 2.2.4 via PR 39806 URL: https://issues.apache.org/bugzilla/show_bug.cgi?id=39806 As well as the BALANCER_ROUTE_CHANGED environment variable added in 2.2.4. This functionality is needed so that an RHEL 5 server can be used as the "front end load palancing proxy" to backend servers running a PHP web application.
Thanks for filing the report. We are rebasing mod_proxy to 2.2.9 in 5.4, which brings in the fix for this bug. *** This bug has been marked as a duplicate of bug 252024 ***