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From Rainer Jung <>
Subject Re: mod_jk, lb cluster, multiple web servers
Date Mon, 03 Mar 2008 23:25:25 GMT
Tim Alberts schrieb:
>> By cluster here we mean a farm (i.e. multiple nodes carrying the same 
>> apps) but not session replication?
> Well I use the setting for 'sticky_session' in the load balancer.  As I 
> understand, it doesn't 'replicate' sessions on multiple servers, but 
> checks the request URL to send a request from the same client to the 
> same server throughout the session.
> What I remember when I researched my initial setup of the servers is, 
> there was no 'session replication' so multiple tomcat servers know about 
> every session simultaneously so request can go to any server without 
> loosing the session.  Has this changed, or am I just confused again?

No change. Without special setup there is no session replication, and 
before you want to try that you first want to understand a stable sticky 
load balancing. I only wanted to be sure, we are "only" talking about 
sticky balancing.

>>> 'local' web server will mount the lb cluster when I only have one 
>>> tomcat6 instance listed in the cluster.  The 'www' web server won't 
>>> mount the cluster if it's 3 or 1 tomcat6 instance.  It will mount a 
>>> tomcat6 instance without the cluster.
>>> I seem to be lacking some understanding.  Can multiple web servers 
>>> connect to tomcat6 with mod_jk at the same time, or do I need to 
>>> configure additional connectors for each connection?
>> No, what you are trying to achieve is very normal. The below config 
>> tells us, that the URLs configured in JkMount are send to a load 
>> balancing woker lb, and although you defined three ajp13 workers, the 
>> lb only knows about one of them, "cartman". So lb should send all 
>> requests to cartman.
> I wasn't clear enough in my original post.  The below configuration 
> works for the www server.  When I add the other 2 nodes to the lb 
> (,stan,kyle) I get internal server 
> error (if I remember correctly).

Internal server error sounds bad. Any info in the web server error log?

If you are going to retest, I would consider downloading sources of 
mod_jk 1.2.26 and doing build by yourself. If you have the usual gcc 
tool chain on your Linux system, the build should be very simple and 
you'll have a binary that definitely fits your environment.

Not saying, that your 1.2.23 binary is the cause of the problem, but 
starting with a local build rules out some possibilities. Also there 
were a number of bugs fixed between 1.2.23 and 1.2.26 (although none of 
them directly related to your observation).



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