7.6 EJB high availability and failover
Many J2EE applications rely on Enterprise JavaBeans (EJBs) to implement key business logic. Therefore, providing a resilient and highly available EJB runtime system is a critical task for any EJB container provider. WAS V6 satisfies this requirement for EJB applications by providing an advanced high availability (HA) solution which guarantees that EJB requests can be serviced continuously even during various types of failures.
The EJB HA solution is not an isolated implementation; instead, it is part of a broader scope of HA solutions provided by WebSphere as core services to almost all kinds of J2EE components running in WebSphere. Please refer to Chapter 9, WebSphere HAManager for details.
When an EJB client makes calls from within the WebSphere container, client container or outside of a container, the request is handled by the EJB container in one of the cluster members. If that cluster member fails, the client request is automatically redirected to another available server. In IBM WAS ND V6, the EJB HA is achieved by a combination of three WebSphere services: the HAManager, the EJB server cluster and EJB workload management (WLM).