High Availability and Failover

An AS Java cluster has the following single points of failure (SPOF):

·        Database

·        Enqueue Service

·        Message Service

The other cluster elements (dispatcher and server processes) represent no SPOFs in the sense that a breakdown in one of them would not affect the entire system.

·        The dispatcher is stateless, this means that running transactions are not hindered. It can be restarted, or from the outset, two dispatchers can be started.

·        If a server process fails, the session is terminated. One way of getting round this problem is to make the session persistent.

For more information about failover at application level, see:

·        Failover for J2EE Web Applications

·        Failover for RMI-P4 Applications

New Communication Schema

The figure below shows the cluster elements and the communication between them. The single points of failure are shown at the bottom.

You can see that the server processes do not communicate with each other. The advantage of this communication schema is that the number of connections only increases linearly with the number of server processes.

Additional Information

For more information, see the complete SAP NetWeaver AS Java: High Availability documentation.