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From Mårten Svantesson <>
Subject Error 503 on shutting down instance of failover cluster
Date Wed, 01 Oct 2008 12:48:01 GMT

This is actually a question regarding the combination of JBoss 4.0.2RC1 with Tomcat 5.0.28
as a component, and Apache 2.2.3 with mod_proxy_ajp. I hope
this is the correct forum.

To get failover we have two machines, both running Apache and JBoss. mod_proxy_ajp is configured
on both machines to do load balancing between the two
JBoss instances. We also use sticky sessions.

The problem is that if you shut down JBoss on one machine (typically to upgrade our application)
and the JBoss currently is "busy" Apache may give you
errors: Status 503 Service temporarily unavailable.

I can see the following lines in the log:

2008-09-10 18:40:33,664 DEBUG [tomcat.localhost.ROOT.Context] Stopping
2008-09-10 18:40:33,665 DEBUG [tomcat.localhost.ROOT.Context] Stopping filters
A bunch of filters are shut down.
2008-09-10 18:40:33,679 DEBUG [tomcat.localhost.ROOT.Context] Processing standard container
2008-09-10 18:40:33,685 INFO  [org.apache.catalina.core.StandardWrapper] Waiting for 14 instance(s)
to be deallocated

It seems like new requests that happen to be given to this Tomcat (by proxy_ajp) are not getting
any responses until somewhere around when this turns
up in the log:

2008-07-08 14:27:39,622 DEBUG [org.jboss.web.tomcat.tc5.Tomcat5]  Destroyed jboss.web:service=WebServer

It seems like the Tomcat threads don't disconnect (from proxy_ajp) until they are destroyed,
even though no incoming requests are handled. The gap in
time between stopping and destroying Tomcat seems to be due to dependencies on components
(MBeans) that are busy.

I can't see any reason for the idle connections to be open, so maybe it is possible to close
those on stopping one of the MBeans of our application.
What do you think?

We used mod_jk with Apache 1.3 before and the problem got a slightly different symptom there,
instead of getting an error message the response from
Apache was empty.

  Mårten Svantesson
  Senior Developer
  Travelocity Nordic
  +46 (0)8 505 787 23

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