High availability manager



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WebSphere Application Server includes a high availability manager (HAM) component whose main function is to eliminate single points of failure.

HAM runs inside the JVM of a WAS cell and and ensures that key services stay running by employing a strategy that moves sessions between available application servers, rather than relying on dedicated sessions to a single appserver, which is the strategy employed by the deployment manager. HAM provides peer-to-peer failover for critical services.

HAM takes advantage of fault tolerant storage technologies such as network attached storage (NAS)

HAM is responsible for managing the availability of singletons within the cell. Examples of singletons include:

HAM continually monitors the application server environment. If an application server component fails, the HAM takes over the in-flight and in-doubt work for the failed server. This action significantly improves application server availability.

In a highly available environment, all single points of failure are eliminated. Because the HAM function is dynamic, any configuration changes that you make and save while an application server is running are eventually be picked up and used. You do not have to restart an application server to enable a change. For example, if you change a policy for a messaging engine high availability group while the messaging engine is running, the new policy is dynamically loaded and applied, and the behavior of the messaging engine reflects this change.

To provide this focused failover service, the HAM supervises the JVMs of the application servers that are core group members. The HAM uses one of the following methods to detect failures: