Oracle WebLogic Server 11g Administration Handbook

What Is a WebLogic Server Cluster?

A WebLogic Server cluster consists of multiple WebLogic Server server instances running simultaneously and working together to provide increased scalability and reliability. A cluster appears to clients to be a single WebLogic Server instance. The server instances that constitute a cluster can run on the same mach... See more

When you create a domain with multiple Managed Servers, all those servers function independent of each other. A cluster, on the other hand, is a group of WebLogic Server instances that work as a single instance from the point of view of a client. The reason you use a cluster is to increase scalability and reliability by taking advantage of a cluste... See more