EJBs and Clustering
EJBs can be configured to operate in a
clustered environment, leveraging WebLogic’s support
for load balancing and failover. In a single-server configuration,
the client uses WebLogic-specific stubs corresponding to the
EJBHome and EJBObject
interfaces. When you deploy EJBs to a WebLogic cluster or to multiple
Managed Servers, WebLogic supplies specialized versions of the EJB
home and EJB object stubs. Both of these stubs provide load-balancing
and failover support, first at the level of looking up a home object,
and second at the level of invoking an EJB method. As discussed in
Chapter 4, any of the features of
WebLogic’s clustered EJB support come directly from
the operation of RMI objects in a clustered environment.
A cluster-aware EJBHome stub knows about the
EJBHome objects on all WebLogic servers in the
cluster. Client calls to the home stub are load-balanced between the
servers to which the EJB has been deployed. The cluster-aware stub
also provides failover for lookup requests by automatically routing
requests to another available server in the cluster, when the
original server hosting an EJB becomes unreachable. WebLogic supports
clustered home stubs for all the EJB types — the
home-is-clusterable element in the
weblogic-ejb-jar.xml descriptor file determines
whether the home object for an EJB is cluster-aware. If you specify
true as the value of this setting, the EJB compiler ensures that the home stubs for the EJB are cluster-aware. By default, EJB ...
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