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From "Martin Registe, Jr." <>
Subject RE: Setup of with multiple host and TC instances
Date Thu, 22 Mar 2012 21:08:20 GMT

Let me see if I've got this straight. You've got:
* A hw load-balancer out front
* 5 physical servers each running:
 - 1 Apache httpd
 - 2 Tomcats

This allows you to have physical-server redundancy (x5) and also the ability to take one TC
instance down on each server for maintenance while leaving the other one running. Right?

Yes this is correct

First question: do all httpd instances know about all Tomcat instances? Or, does httpd only
know about the two instances that are co-located with it on 
the same physical server?

Httpd only know about the two instances that re collocated with it on the same physical server

If https only knows about its local 2 Tomcat instances, then you'll only need 2 workers, etc.
I have no idea how this could possibly work with sticky sessions unless the hw lb knows how
to dispatch to the right http/2xTomcat physical server, in which case you are wasting your
time with all these extra processes.

The hw loadbalancer sends the traffic to port 80...
apache takes it and using the file sends it to one of TC instances 
then apache sends it back through the hw lb it has a sessionid and jvm tag on in the host
header so it knows which jvm it came from

What about <Engine>? It would be nice to confirm that your jvmRoute(s)
is(are) set correctly.

TC1    <Engine name="Catalina" defaultHost="localhost" jvmRoute="jvm1">
TC2    <Engine name="Catalina" defaultHost="localhost" jvmRoute="jvm2">

That depends. The host should always be "localhost", since your httpd instances only talk
to the co-located Tomcats, right?


My next thoughts
I don't know exactly how this is working but it definitely is working and doesn't seem to
be getting sessions jumping from one jvm to the other (on the same physical server).  I will
play around with the configuration some more but this has been working for over a year.  You
are saying if I just go with 



everything will continue to work, correct?


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