Websphere 6.1 Network Deployment App Server Package provides out-of-the-box support for clustering, thus providing for fail-over and load-balancing.
In a cluster, WAS provides data-replication services for 'session' data, 'WAS dynamic cache' data, etc. across member in a cluster.
But it does not provide replication of objects stored in the Application context or Servlet Context across the nodes of the cluster.
Hence if Ur application relies on state stored in the App Context, then it would fail in a cluster unless U make sure that all the concerned requests (which expect objects in the context) have the same JSESSIONID cookie and session affinity is configured on WAS. In this case, the WAS infrastructure would consider the jsession id present in the request and forward the request to the appropriate Appserver.
Another solution is to use a database or a file and not the Servlet Context for storing data to be shared across sessions.