Weblogic Server Clustering
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 machine, or be located on different machines.
You can increase a cluster’s capacity by adding additional server instances to the cluster on an existing machine, or you can add machines to the cluster to host the incremental server instances.
Each server instance in a cluster must run the same version of WebLogic Server.
How Does a Cluster Relate to a Domain?
A cluster is part of a particular WebLogic Server domain.
A domain is an interrelated set of WebLogic Server resources that are managed as a unit.
A domain includes one or more WebLogic Server instances, which can be clustered, non-clustered, or a combination of clustered and non-clustered instances.
A domain can include multiple clusters.
Benefits of Clustering?
The capacity of an application deployed on a WebLogic Server cluster can be increased dynamically to meet demand. You can add server instances to a cluster without interruption of service—the application continues to run without impact to clients and end users.
In a WebLogic Server cluster, application processing can continue when a server instance fails. You “cluster” application components by deploying them on multiple server instances in the cluster—so, if a server instance on which a component is running fails, another server instance on which that component is deployed can continue application processing.
WebLogic Server Communication In a Cluster
WebLogic Server instances in a cluster communicate with one another using two basic network technologies:
IP sockets, which are the conduits for peer-to-peer communication between clustered server instances.
IP unicast or multicast, which server instances use to broadcast availability of services and heartbeats that indicate continued availability.
Key Capabilities of a Cluster