When your business process is configured for clustering, the BPEL Service Engine's failover capabilities ensure throughput of running business process instances. When business process instances encounter an engine failure, any suspended instances are picked up by all available BPEL Service Engines.
To configure failover, in the BPEL Service Engine properties, set the EngineExpiryInterval property so that it registers itself as alive frequently enough to meet the demands of your system. Optimizing this property setting might require some testing. The default setting is 15.