Cluster Basics

To run session replication in your Tomcat 8 container, the following steps should be completed:

• All your session attributes must implement java.io.Serializable
• Uncomment the Cluster element in server.xml
• If you have defined custom cluster valves, make sure you have the ReplicationValve defined as well under the Cluster element in server.xml
• If your Tomcat instances are running on the same machine, make sure the tcpListenPort attribute is unique for each instance, in most cases Tomcat is smart enough to resolve this on it’s own by autodetecting available ports in the range 4000-4100
• Make sure your web.xml has the <distributable/> element
• If you are using mod_jk, make sure that jvmRoute attribute is set at your Engine <Engine name=”Catalina” jvmRoute=”node01″ > and that the jvmRoute attribute value matches your worker name in workers.properties
• Make sure that all nodes have the same time and sync with NTP service!
• Make sure that your loadbalancer is configured for sticky session mode.

Load balancing can be achieved through many techniques, as seen in the Load Balancing chapter.

Note: Remember that your session state is tracked by a cookie, so your URL must look the same from the out side otherwise, a new session will be created.

Note: Clustering support currently requires the JDK version 1.5 or later.

The Cluster module uses the Tomcat JULI logging framework, so you can configure logging through the regular logging.properties file. To track messages, you can enable logging on the key:org.apache.catalina.tribes.MESSAGES