Apache HTTP Server/Tomcat Load Balancing Problem

I am trying to load balance our web based application using Apache HTTP Server and Tomcat on Linux.

I think I have setup the environments correctly, although I am not sure of the configuration parameters for either apache or tomcat. We have apache running on one linux server and 2 instances of tomcat running on two nodes with linux installed.

I am using JMeter to test the load on our app. I can get JMeter to send 30 simultanous requests (num of users)  for 4 consecutive intervals in each thread group, however as I change the number of users to 35, I start getting
"HTTP response code: 500
HTTP response message: Internal Server Error" errors.

As I monitor apache's log file, I can see it is receiving all the POST requests, however it seems to me like it is not able to send them all to its workers, tomcat1 and tomcat2, or workers are not capable of accepting and serving these requests.

If you have any suggestions/recommendations on how to configure apache or tomcat to handle more simultanous users, please advise.

I am using:
apache 2.2
mod_jk: download   mod_jk-1.2.21-apache-2.2.x-linux-i686.so
tomcat 5.5.12
jrockit r27

Thank you,
Who is Participating?
Mayank SConnect With a Mentor Associate Director - Product EngineeringCommented:
Yes that is why Tomcat was getting those time out exceptions and showing you a 500 ;)
Mayank SAssociate Director - Product EngineeringCommented:
Are there any error logs in Tomcat's logs? 500 internal error would mean some exception was thrown on the server side. Are you closing your connections, etc properly in finally blocks? Also ensure you don't store any state in the servlets and if you do then they should be thread safe. Difficult to say what it is without knowing what your application does.
NoushinBAuthor Commented:
After turning on exception handling, we noticed our calls to web services were timing out. We increased our WS timeout setting and the application proceeded successfully. Thanx.
Forced accept.

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