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High Availability Manager (HAManager) enhances the availability of singleton services in WebSphere. These singleton services include:
| Transaction service - Transaction log recovery |
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| Messaging service - Messaging engine restarting |
The HAManager runs as a service within each WebSphere process (Deployment Manager, Node Agents, or appservers) that monitors the health of WebSphere singleton services. In the event of a server failure, the HAManager will failover any singleton service that was running on the failed server to a peer server. Examples of such a failover include the recovery of any in-flight transactions or restarting any messaging engines that were running on the failed server. As depicted in Figure 6-1, each appserver process runs a HAManager component and shares information through the underlying communication infrastructure Distribution and Consistency Services (DCS) such that no single point of failure would exist in the topology. Every member in a WebSphere cluster knows where singleton services are running.
Figure 6-1 HAManager architecture
This peer-to-peer failover model dramatically improves recovery time. Also, WebSphere clusters can be made highly available with a simpler setup. No external high availability software is required.
Deployment Managers and Node Agents cannot be made highly available with HAManager. Refer to Part 5, Using external clustering software for information about how to achieve this.
