WebLogic Server clusters provide scalability and reliability for your applications by distributing the work load among multiple instances of WebLogic Server. Incoming requests can be routed to a WebLogic Server instance in the cluster based on the volume of work being processed. In case of hardware or other failures, session state is available to other cluster nodes that can resume the work of the failed node.
A WebLogic server cluster consists of multiple WebLogic server instances running simultaneously 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.
Note: Each server instance in a cluster must run the same version of WebLogic.
Relationship between Clusters and Domains
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. A domain also contains the application components deployed in the domain, and the resources and services required by those application components and the server instances in the domain. Examples of the resources and services used by applications and server instances include machine definitions, optional network channels, connectors, and startup classes.
In each domain, one WebLogic server instance acts as the Administration Server—the server instance that configures, manages, and monitors all other server instances and resources in the domain. Each domain contains one Administration Server only. If a domain contains multiple clusters, each cluster in the domain has the same Administration Server. All server instances in a cluster must reside in the same domain; you cannot split a cluster over multiple domains. Similarly, you cannot share a configured resource or subsystem between domains.
Clustered WebLogic server instances behave similarly to non-clustered instances, except that they provide failover and load balancing. The process and tools used to configure clustered WebLogic server instances are the same as those used to configure non-clustered instances. However, to achieve the load balancing and failover benefits that clustering enables, you must adhere to certain guidelines for cluster configuration.
High Availability with WebLogic Clustering
P6 EPPM can utilize WebLogic clustering to continue processing data when a server instance fails. You cluster P6 EPPM by deploying it on multiple server instances in the cluster. If a server instance on which P6 EPPM is running fails, then another running server instance on which P6 EPPM is deployed can continue to process data.
For a more comprehensive product overview, documentation, and community forums for WebLogic and its clustering functionality, see http://www.oracle.com/technetwork/middleware/weblogic/overview/index.html