The heart of WebLogic's load-balancing schemes lies in its clustered JNDI and RMI implementation, described in Chapter 4. As the overview pointed out, the replica-aware stubs maintained by the cluster allow calls to the RMI object to be routed to any of the servers in the cluster hosting that object. This scheme underlies WebLogic's support of load balancing for JDBC data sources, EJBs, and distributed JMS destinations, as all of these are implemented using RMI. The rest of this section describes these load-balancing schemes and some of the general conditions under which they will and won't be used.
Both WebLogic 8.1 and 7.0 support several algorithms for balancing requests to clustered objects: round-robin, weight-based, random, and parameter-based routing. By default, WebLogic uses a round-robin policy for load balancing. An example of a server-to-server scenario was illustrated in Figure 14-1, where a JSP deployed to a presentation tier makes a call to an EJB or RMI object deployed to a separate object tier cluster. The algorithm used to choose between the servers in the object tier cluster depends on two factors:
If the RMI object was compiled with a particular load-balancing scheme, that scheme will be used.
If no scheme was explicitly configured, the default load-balancing scheme for the cluster will be used.
You can configure the default load-balancing scheme for the cluster by selecting the cluster in the Administration Console ...