What Is a WebLogic Server Cluster? WebLogic Server Clusters and WebLogic Server Domains

3 High Availability for WebLogic Server 3-1 3 High Availability for WebLogic Server This chapter describes the Oracle WebLogic Server high availability capabilities used to provide Oracle Fusion Middleware high availability. ■ Section 3.1, What Is a WebLogic Server Cluster? ■ Section 3.2, WebLogic Server Clusters and WebLogic Server Domains ■ Section 3.3, Benefits of Clustering ■ Section 3.4, Key Capabilities of a Cluster ■ Section 3.5, Types of Objects That Can Be Clustered ■ Section 3.6, Communications in a Cluster ■ Section 3.7, Cluster-Wide JNDI Naming Service ■ Section 3.8, Failover and Replication in a Cluster ■ Section 3.9, Whole Server Migration ■ Section 3.10, JMS and JTA High Availability ■ Section 3.11, Administration Server and Node Manager High Availability ■ Section 3.12, Load Balancing ■ Section 3.13, Multi Data Sources ■ Section 3.14, Cluster Configuration and config.xml ■ Section 3.15, About Singleton Services ■ Section 3.16, WebLogic Server and LDAP High Availability For complete documentation of Oracle WebLogic Server clustering, see Oracle Fusion Middleware Using Clusters for Oracle WebLogic Server. 3.1 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 system, or be located on different systems. You can increase a clusters capacity by adding additional server instances to the cluster on an existing system, or you can add systems to the cluster to host the incremental server instances. Each server instance in a cluster must run the same version of WebLogic Server. 3-2 Oracle Fusion Middleware High Availability Guide

3.2 WebLogic Server Clusters and WebLogic Server Domains

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. 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 system definitions, optional network channels, connectors, and startup classes. In each domain, one WebLogic Server instance acts as the Administration Server—the server instance which configures, manages, and monitors all other server instances and resources in the domain. Each Administration Server manages one domain 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. For example, if you create a JDBC connection pool in one domain, you cannot use it with a server instance or cluster in another domain. Instead, you must create a similar connection pool in the second domain. 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.

3.3 Benefits of Clustering