Stateful session bean failover
In WAS on z/OS, the distribution of IIOP requests is handled by the Location Service Daemon. When a request for an EJB lookup arrives at the controller region, the controller region points the requestor to the Location Service Daemon. Then the requestor sends a locate request to the daemon, the daemon assigns a controller to the client, one of the servants of the assigned controller creates the EJB and all subsequent calls to the EJB from the same requestor go through the same controller.
The state replication of a stateful session bean is also based on DRS, similar to HTTP session replication.
The J2EE 1.4 specification requires HTTP session state objects to be able to contain local references to EJBs. Using local references to EJBs has big performance advantages. WAS V6 can collocate stateful session bean replicas and HTTP session replicas for hot failover. In other words, if an HTTP session object in a server contains a local reference to a stateful session EJB instance in the same server, both HTTP session and EJB session are replicated to the same replica in the replication domain. In case of a failover, the HTTP session still holds the local reference to the EJB and is able to locate the local session EJB instance.
Another aspect regarding WebSphere z/OS EJB session failover is failover among servant regions for unmanaged servers. In an unmanaged z/OS server, stateful session bean failover among servants can be enabled. Failover only occurs between the servants of a given unmanaged server. If an unmanaged z/OS server has only one servant, then enabling failover has no effect. To enable failover between servants in an unmanaged server, use the Administrative Console to add a new custom property called...
EJBContainerEnableUnmanagedServerReplication...to the servant JVMs and set it to true.
Because you might not want to enable failover for every single stateful session bean in the EJB container, you can override the EJB container settings at either the application or EJB module level. You can either enable or disable failover at each of these levels. This is the same as WebSphere on other platforms. See Stateful session bean failover for more information about this topic.
To enable sysplex-wide distribution of EJB requests, a WAS and its Location Service Daemon must be started on each system. A DVIPA can be used as the sysplex-wide Location Service Daemon IP. The Sysplex Distributor uses this IP to balance requests across the systems. In this configuration, the stateful session EJB sessions must be replicated using DRS. Also, a shared HFS should be used for passivating EJBs.