A distributed session can run in multiple Sun Java System Application Server instances, if:
Each server instance has access to the same session state data. Application Server provides the following types of high availability storage for HTTP session and stateful session bean data:
In-memory replication on other servers in the cluster. In-memory replication is enabled by default with the cluster profile.
The use of in-memory replication requires the Group Management Service (GMS) to be enabled. For more information about GMS, see Group Management Service.
If server instances in a cluster are located on different machines, ensure that the following prerequisites are met:
To ensure that GMS and in-memory replication function correctly, the machines must be on the same subnet.
To ensure that in-memory replication functions correctly, the system clocks on all machines in the cluster must be synchronized as closely as possible.
High-availability database (HADB). For information about how to enable this database, see configure-ha-cluster(1).
The HADB software is supplied with the Application Server standalone distribution of Sun Java System Application Server. For information about available distributions of Sun Java System Application Server, see Distribution Types and Their Components in Sun Java System Application Server 9.1 Installation Guide. HADB features are available only in the enterprise profile. For information about profiles, see Usage Profiles in Sun Java System Application Server 9.1 Administration Guide.
Each server instance has the same distributable web application deployed to it. The web-app element of the web.xml deployment descriptor file must contain the distributable element.
The web application uses high-availability session persistence. If a non-distributable web application is configured to use high-availability session persistence, the server writes an error to the log file.