23 Using Clusters and High Availability Features

23.1 About Clusters and High Availability Features

One of the most important factors in both high availability and performance is the use of clusters. A cluster is a set of processes running on single or multiple computers that share the same workload. Using a clustered configuration promotes scalability, high availability, and performance.

High availability refers to the ability of users to access a system without loss of service. Deploying a high availability system minimizes the time when the system is down, or unavailable and maximizes the time when it is running, or available. See

Details about using clusters and other high availability features can be located in the application-specific guides listed in Table 23-1:

23.2 Using Clusters with Oracle Fusion Middleware

For production environments that require increased application performance, throughput, or high availability, you can configure two or more Managed Servers to operate as a cluster. A cluster is a collection of multiple Oracle WebLogic Server server instances running simultaneously and working together to provide increased scalability and reliability.

For more information on using clusters with Oracle Fusion Middleware, see the following:

• "Understanding Managed Servers and Managed Server Clusters" in Oracle Fusion Middleware Administrator's Guide

• Oracle Fusion Middleware Using Clusters for Oracle WebLogic Server

• Oracle Real Application Clusters Administration and Deployment Guide

23.3 Using High Availability Features with Oracle Fusion Middleware

In addition to using a clustered architecture within your Fusion Middleware components, there are a number of high availability features built-in to ensure your applications are continuously accessible by the users. The following list provides a few options for setting up a comprehensive high availability system. The options that you integrate depend on your overall performance goals as well as your system architecture. This list is meant to provide examples only.

• Process death detection and automatic restart

  Processes may die unexpectedly due to configuration or software problems. A proper process monitoring and restart system should constantly check the health of the applications and restart them when problems appear.

  A system process should also maintain the number of restarts within a specified time interval. This is also important since continually restarting within short time periods may lead to additional faults or failures. Therefore a maximum number of restarts or retries within a specified time interval should also be designed as well.

• State replication and routing

  For stateful applications, client state can be replicated to enable stateful failover of requests in the event that processes servicing these requests fail.

• Failover

  With a load-balancing mechanism in place, the instances are redundant. If any of the instances fail, requests to the failed instance can be sent to the surviving instances.

• Server load balancing

  When multiple instances of identical server components are available, client requests to these components can be load balanced to ensure that the instances have roughly the same workload.

• Disaster Recovery

  Disaster recovery solutions typically set up two homogeneous sites, one active and one passive. Each site is a self-contained system. The active site is generally called the production site, and the passive site is called the standby site. During normal operation, the production site services requests; in the event of a site failover or switchover, the standby site takes over the production role and all requests are routed to that site. To maintain the standby site for failover, not only must the standby site contain homogeneous installations and applications, data and configurations must also be synchronized constantly from the production site to the standby site.

For more information see the Oracle Fusion Middleware High Availability Guide.