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From Christopher Schultz <>
Subject Re: Error 503 ocurring when server under load
Date Thu, 07 Oct 2010 22:17:41 GMT
Hash: SHA1


On 10/7/2010 12:59 PM, Rob G wrote:
> Recently migrated a production site (mixture of Servlets and JSPs)
> from Oracle Application Server to Apache/Tomcat. Since then we have
> seen numerous HTTP Error 503 - Service unavailable errors at peak
> times when site is under load. mod_jk.log has the following error
> message(s):
> [2184:1952] [error] jk_lb_worker.c (1473): All tomcat instances
> failed, no more workers left

Just to reinforce a comment by Andre, I think you might want to compare
the request processor counts you have for Tomcat versus mod_jk: the
default maxThreads for a Tomcat <Connector> is 200, while your
MaxClients settings might be different on your Apache httpd configuration.

If you have httpd.MaxClients=250 and connector.maxThreads=200 then you
have a deficit of 50 who will get 503 errors if they try to access your
webapp during peak load.

> Apache: 2.2.16

I believe that only the Worker MPM is available on Microsoft Windows.
Have you explicitly configured an MPM?

> worker.worker1.cachesize=10

You might want to read the documentation for worker.cachesize in

Note that it's deprecated and you should use connection_pool_size instead.

Since you're using Apache 2.x, mod_jk should be able to auto-configure
this value for you.

- From my reading, you may be limiting yourself to 10 simultaneous
connections from Apache httpd to Tomcat, and others will get a 503.
Rainer or Mladen will have to comment to clarify: I am certainly no
expert in mod_jk configurations.

Hope that helps,
- -chris
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Comment: Using GnuPG with Mozilla -


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