Using WebLogic Server Clusters

Introduction and Roadmap

This section describes the contents and organization of this guide—Using WebLogic Server® Clusters.

Document Scope and Audience

This document is written for application developers and administrators who are developing or deploying Web-based applications on one or more clusters. It also contains information that is useful for business analysts and system architects who are evaluating WebLogic Server or considering the use of WebLogic Server clusters for a particular application.

The topics in this document are primarily relevant to planning, implementing, and supporting a production environment that includes WebLogic Server clusters. Key guidelines for software engineers who design or develop applications that will run on a WebLogic Server cluster are also addressed.

It is assumed that the reader is familiar with J2EE, HTTP, HTML coding, and Java programming (servlets, JSP, or EJB development).

Guide to this Document

This chapter, Introduction and Roadmap, describes the organization of this guide.
Understanding WebLogic Server Clustering
Communications in a Cluster
Understanding Cluster Configuration
Load Balancing in a Cluster
Failover and Replication in a Cluster
Cluster Architectures
Setting up WebLogic Clusters
Clustering Best Practices
Troubleshooting Common Problems
The WebLogic Cluster API
Configuring BIG-IP^TM Hardware with Clusters.

New and Changed Clustering Features in This Release

The new features in WebLogic Server 9.0 that relate to clustering are describe in the following sections.

Server Migration

Note: Server Migration is not supported on all platforms. See Server Migration in Supported Configurations for WebLogic Server 9.0.

WebLogic Server 9.0 supports automatic and manual migration of a clustered server instance from one machine to another. A Managed Server that can be migrated is referred to as a migratable server. This feature is designed for environments with requirements for high availability.The server migration capability is useful for:

Ensuring uninterrupted availability of singleton services—services that must run on only a single server instance at any given time, such as JMS and the JTA transaction recovery system, when the hosting server instance fails. A Managed Server configured for automatic migration will be automatically migrated to another machine in the event of failure.
Easing the process of relocating a Managed Server, and all the services it hosts, as part of a planned system administration process. An administrator can initiate the migration of a Managed Server from the Administration Console or command line.

The server migration process relocates a Managed Server in its entirety—including IP addresses and hosted applications—to on of a predefined set of available host machines.

Note: Previous releases of WebLogic Server provided the ability to migrate an individual singleton service from one server instance to another. This capability is still supported in WebLogic Server 9.0.

For more information see Server Migration.

Cross-cluster Replication

WebLogic Server 9.0 supports failover across logically or physically separate clusters. The following failover mechanisms are provided:

MAN HTTP Session State Replication

Allows you to replicate HTTP session state synchronously across clusters. You can set up primary and secondary servers in separate clusters. If the primary server in one cluster fails, session state can be replicated to a secondary server in another cluster.
This feature allows you to isolate a cluster, for example in one physical location, power grid, or ISP, while maintaining high availability by allowing failover to another cluster in a separate location.

WAN HTTP Session State Replication

Provides HTTP session state replication across geographically separated clusters. Uses in-memory replication within a cluster and asynchronously persists state to a database in the secondary cluster.

Dynamic Generation of Cluster Address

In previous releases, it was necessary to explicitly define a cluster address when configuring a cluster.

In WebLogic Server 9.0 you can still explicitly define a cluster address, but if you do not, WebLogic dynamically generates the cluster address for each request. For more information, see Cluster Address.