Rob G wrote:
Hey all,
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
I'm looking for help in trying to tweak settings to prevent this, or
confirmation that I've configured the setup correctly.
Many thanks
Rob
Platform:
Windows Server 2003 SP2
Setup:
Two tomcat instances with a single Apache front end, all on the same server
Versions
Tomcat: 6.0.24
Apache: 2.2.16
mod SSL: 2.2.16
Open SSL: 0.9.8
mod_JK:1.2.30
Your configuration looks very clean to me (no unnecessary settings etc.), which in this
case is a plus (a good base to start tuning).
You may want to upgrade Tomcat to the latest version (6.0.29).
But before you start tuning, you should get some idea of what is actually going
on.
For example, at the moment these errors happen, what are these Tomcats really
doing ?
Are they really busy each processing 200 requests, with 200 threads running and actually
doing something ? (200 is the default for the "maxThreads" attribute of the AJP Connector).
If yes, then you may just need a leaner application, or a bigger system (more RAM, faster
CPU), or more systems. What does the Task Manager tell you about the total system load ?
If not, and many of these threads are waiting, then you may have an issue with a keepAlive
that is too long.
See http://tomcat.apache.org/tomcat-6.0-doc/config/ajp.html, for the connectionTimeout and
keepAliveTimeout attributes.
Whatever you do, first get an idea of the starting situation. Then modify one setting at
a time, and observe (and note) the effects.
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