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18.6. Configuring HTTP session state replication

The preceding discussion has been focused on using mod_jk as a load balancer. The content of the remainder our discussion of clustering HTTP services in JBoss AS applies no matter what load balancer is used.

In Section 18.4, “Configure worker nodes in mod_jk”, we covered how to use sticky sessions to make sure that a client in a session always hits the same server node in order to maintain the session state. However, sticky sessions by themselves are not an ideal solution. If a node goes down, all its session data is lost. A better and more reliable solution is to replicate session data across the nodes in the cluster. This way, the client can hit any server node and obtain the same session state.

The jboss.cache:service=TomcatClusteringCache MBean makes use of JBoss Cache to provide HTTP session replication services to the JBoss Tomcat cluster. This MBean is defined in the deploy/jboss-web-cluster.sar/META-INF/jboss-service.xml file.


Before AS 4.2.0, the location of the HTTP session cache configuration file was deploy/tc5-cluster.sar/META-INF/jboss-service.xml. Prior to AS 4.0.4 CR2, the file was named deploy/tc5-cluster-service.xml.

Below is a typical deploy/jbossweb-cluster.sar/META-INF/jboss-service.xml file. The configuration attributes in the TomcatClusteringCache MBean are very similar to those in the JBoss AS cache configuration.

<mbean code="org.jboss.cache.aop.TreeCacheAop"


    <attribute name="TransactionManagerLookupClass">
    <attribute name="IsolationLevel">REPEATABLE_READ</attribute>
    <attribute name="CacheMode">REPL_ASYNC</attribute>
    <attribute name="ClusterName">
    <attribute name="UseMarshalling">false</attribute>
    <attribute name="InactiveOnStartup">false</attribute>
    <attribute name="ClusterConfig">
        ... ...
    <attribute name="LockAcquisitionTimeout">15000</attribute>
    <attribute name="SyncReplTimeout">20000</attribute>

Note that the value of the mbean element's code attribute is org.jboss.cache.aop.TreeCacheAop, which is different from the other JBoss Cache Mbeans used in JBoss AS. This is because FIELD granularity HTTP session replication (covered below) needs the added features of the TreeCacheAop (a.k.a. PojoCache) class.

The details of all the configuration options for a TreeCache MBean are covered in the JBoss Cache documentation. Below, we will just discuss several attributes that are most relevant to the HTTP cluster session replication.