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From Rob Block <>
Subject ANN: scalable clustered session manager
Date Tue, 22 Feb 2005 08:59:19 GMT
Tomcat users,

I have created a plugin for Tomcat 5 that provides scalable session
clustering by replicating each session to a single node rather than
the whole cluster.  For large-cluster deployments (the primary target
audience of this work), the resource savings for both bandwidth and
per-node memory usage can be dramatic compared to the current full
replication scheme.

The tomcat plugin is hosted at (formerly home to the
full-replication jgroups-based session manager that is now integrated
into Tomcat 5).  The initial (alpha quality) release of the plugin is
available to users and developers now and is under active

To download the plugin: go to tomcat-jg site (above) and select
tomcat-jcluster package under File Releases.  It contains three jar
files, plus release notes for setting it up:

 - catalina-ha.jar – the tomcat plugin 
 - jcluster.jar – jcluster API 
 - jcluster-plugin.jar – jgroups impl of jcluster 

The plugin uses the jcluster API ( for
communication, membership and failover.  Jcluster is a BSD-licensed
set of API’s that specifies group communication functionality similar
to jgroups.  Jgroups is currently required as a separate download as
it is the only jcluster impl.  However, this is only temporary as I
am working on a port to use Tomcat's internal communication classes. 
The jcluster javadoc is online at

The tomcat plugin source is viewable at:

I would appreciate feedback about the usefulness of this project, in
particular, how many of you are deploying Tomcat in large cluster
configurations where current scalability limitations are a concern.

Please address any questions to me at


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