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From "Michael Whiteley" <mwhite...@materialogic.com>
Subject [users@httpd] Possible problem with mod_proxy/mod_proxy_balancer BalancerMembers on Apache 2.2.8+
Date Wed, 08 Apr 2009 20:59:07 GMT
After upgrading from Apache 2.2.6 to Apache 2.2.9, when gracefully shutting down one of our
Embedded Tomcats on our application
server, we notice a temporary outage (503) from our proxy balancer before the Hot Standby
(status=+H) takes over.

Layout:
- Application proxy server (Apache 2.2.9)
   - Proxies requests via mod_proxy/mod_proxy_balancer/mod_proxy_ajp to application server
- Application server (Java)
   - Runs master Java application server with Embedded Tomcat (Tomcat/5.5.17) on port 8009
   - Runs slave Java application server with Embedded Tomcat (Tomcat/5.5.17) on port 8008

When the application proxy server was Apache 2.2.6, we were able to gracefully shutdown the
master Tomcat server (calling
embedded.stop()), and the Hot Standby (status=+H) BalancerMember would immediately start serving
requests.  After the upgrade to
2.2.9, we see "HTTP/1.1 503 This application is not currently available" while the active
BalancerMember is shutting down before the
Hot Standby takes over (~ 1 second). These errors appear in both the Tomcat access log and
the Apache access log.

I have recompiled and tested Apache versions 2.2.6, 2.2.8, 2.2.9 and 2.2.11 to verify that
this problem exists at some point after
version 2.2.6.  I still had the problem when switching the BalancerMember protocol from ajp://
to http://, so I think this rules out
AJP-specific issues.  I was unable to reproduce the problem using Apache servers as the BalancerMembers,
so I'm speculating this has
something to do with the interaction with Tomcat.

Please let me know what other information would be helpful in resolving this issue.

Proxy conf:
=================================
ProxyPassMatch /(.+/)?application.server$		balancer://production_server

<Proxy balancer://production_server/>
	BalancerMember ajp://server.domain.tld:8009/	lbset=1	retry=10	loadfactor=100
	BalancerMember ajp://server.domain.tld:8008/	lbset=2	retry=10	status=+H

	ProxySet lbmethod=bytraffic
</Proxy>
=================================

Thanks,

Michael


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