Velocity, Struts and Tomcat Clusters

I just recently found my self using Tomcat with Velocity and Struts
And as would be expected I needed to use more than one Tomcat server for load balancing and Reliability so I looked into how to Cluster Tomcat.

There are 3 options with tomcat 5.0

1. Save your session to a file
2. Save your session to a database
3. Use Tomcats multicast Replication

I played with #2 and #3 and found out that Velocity puts a Object into the session object that is used to synchronize on.

It creates a empty Object and put it into the Session then when doing any actions it uses the Object as a mutex so that only thread can act on any session. This sounds smart? Right?

Well when I tried to serialize the session I ran into many problems because Object is not serializeable.

I was banging my head against the table over and over trying to figure out why I was getting session.mutex is not serializeable.

Then I had to try and find where session.mutexwas getting put into the session because I knew that I was not doing it

Finally I found out that it was Velocity Tools that was putting an object into the session.

So I the solution was to recompile velocity tools so I could extend it and I do a synchronize on the session itself. Now there are no extra object to passed to the other clusters.

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