Top Level Elements
The Cluster object
The tomcat cluster implementation provides session replication, context attribute replication and
cluster wide WAR file deployment.
Cluster configuration is fairly complex, the default configuration will work
for most people out of the box.
The Tomcat Cluster implementation is very extensible, and hence we have exposed a myriad of options,
making the configuration seem like a lot, but don't lose faith, instead you have a tremendous control
over what is going on.
|Engine vs Host placement|
You can place the
<Cluster> element inside either the
container or the
Placing it in the engine, means that you will support clustering in all virtual hosts of Tomcat,
and share the messaging component. When you place the
<Cluster> inside the
element, the cluster will append the host name of each session manager to the managers name so that two contexts with
the same name but sitting inside two different hosts will be distinguishable.
The session manager element identifies what kind of session manager is used in this cluster implementation.
This manager configuration is identical to the one you would use in a regular
The default value is the
org.apache.catalina.ha.session.DeltaManager that is closely coupled with
SimpleTcpCluster implementation. Other managers like the
are/could be loosely coupled and don't rely on the
SimpleTcpCluster for its data replication.
The Channel and its sub components are all part of the IO layer
for the cluster group, and is a module in it's own that we have nick named "Tribes"
Any configuring and tuning of the network layer, the messaging and the membership logic
will be done in the channel and its nested components.
You can always find out more about Apache Tribes
The Tomcat Cluster implementation uses
Tomcat Valves to
track when requests enter and exit the servlet container. It uses these valves to be able to make
intelligent decisions on when to replicate data, which is always at the end of a request.
The Deployer component is the Tomcat Farm Deployer. It allows you to deploy and undeploy applications
ClusterListener's are used to track messages sent and received using the
If you wish to track messages, you can add a listener here, or you can add a valve to the channel object.
|Deprecated configuration options|
Deprecated settings: In the previous version of Tomcat you were able to control session
manager settings using manager.<property>=value.
This has been discontinued, as the way it was written interferes with
the ability to support multiple different manager classes under one cluster implementation,
as the same properties might have the different effect on different managers.