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From Tim Alberts <>
Subject Re: mod_jk, lb cluster, multiple web servers
Date Mon, 03 Mar 2008 23:06:22 GMT
Rainer Jung wrote:
> Hi Tim,
> Tim Alberts schrieb:
>> I have 3 physical servers, all 3 running tomcat6 and the 2 web 
>> applications (one for local, one for www) just fine.  Two of these 
>> have apache web servers (local and www), both configured and running 
>> static content by themselves just fine.
>> Ideally, I want the 3 tomcat6 instances to be a lb cluster for the 
>> two web servers.  For reasons I don't understand, it isn't working.  The
> 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?

>> '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).

> If you can reproduce your problem with single requests, then you can 
> set your JkLogLevel to debug, restart the web server and send a single 
> request. The log file will tell you, what mod_jk configured during 
> startup, if it found a worker it will send the request to, and what it 
> got back from the worker. I assume, that you already checked, if you 
> have error messages in the JK log file?
I am only at 'info' log level so I haven't seen anything in the log file 
that helped.  I will up the setting and re-test.

> If you add the other two members to the list of members of lb, can you 
> see them in the status worker?
My first answer was yes, but now that you ask I don't remember, I'll 
have to retest that.
> Just in case one of the two web servers uses an even more recent 
> version of mod_jk: we made our vhost handling more strict. JkMounts 
> now have to be inside the VirtualHost (if you use them) or you must 
> use JkMountCopy to inherit mounts from the global server to a vhost.
All mod_jk are the same version.

> Regards,
> Rainer
>> Servers are Apache2.2.3 Tomcat6.0.14 
>> #
>> #
>> # List workers
>> worker.list=lb,jkstatus
>> #
>> # Define cartman
>> worker.cartman.port=8009
>> worker.cartman.type=ajp13
>> worker.cartman.socket_timeout=300
>> worker.cartman.lbfactor=1
>> #
>> # Define stan
>> worker.stan.port=8009
>> worker.stan.type=ajp13
>> worker.stan.socket_timeout=300
>> worker.stan.lbfactor=1
>> #
>> # Define kyle
>> worker.kyle.port=8009
>> worker.kyle.type=ajp13
>> worker.kyle.socket_timeout=300
>> worker.kyle.lbfactor=1
>> #
>> #
>> # Define lb
>> #
>> # Define a 'jkstatus' worker using status
>> worker.jkstatus.type=status
>> Apache config file mounts the local applications like:
>>    JkMount /localapp lb
>>    JkMount /localapp/* lb
>> Apache config file mounts the www applications like:
>>    JkMount /wwwapp lb
>>    JkMount /wwwapp/* lb
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