If one of your connection pools runs out of JDBC connections, the load balancing algorithm may still direct connection requests to the empty pool. Non-clustered services and APIs Several APIs and internal services are not clusterable in WebLogic Server versions 4.5 and 5.1. However, the services do not make use of load balancing or failover features. The JNDI tree lists all of the public objects offered by a server. A server offers a new object by binding a stub representing that object into the JNDI tree.
Clients obtain the stub by connecting to a server and looking up the object by name.
WebLogic Server clusters provide a JNDI tree that contains all of the objects hosted by servers in the cluster. Clients simply connect to a server in the cluster and look up the desired object by name. From the clients' point of view, the lookup procedure is the same regardless of whether or not the object is clustered. For clustered objects, however, the JNDI tree contains replica-aware stubs, which represent object instances that are clustered across multiple servers. In order for a cluster to be scalable, it must ensure that each server is fully utilized.