IBM WAS ND V6 offers a built-in appserver clustering function and the HAManager for protecting WebSphere singleton services. Clustering appservers provides workload management (WLM) and failover for applications that reside on the appserver cluster.

Other clustering techniques can be used for WebSphere end-to-end system high availability, including...

• Database
• LDAP directory server
• Firewalls
• Caching Proxy
• One or more Load Balancers
• HTTP servers

The WebSphere process failover is instantaneous. Be aware, however, that a clustered database server failover (IP-based cluster failover) might take minutes. To minimize the potential downtime, use parallel database servers that are provided by features such as...

• Database Partitioning for DB2 UDB Enterprise Server Edition V8
• Oracle Real Application Clusters (RAC)

There are two kinds of cluster failovers:

1. IP-based cluster failover, such as...
   • IBM High Availability Cluster Multi-Processing for AIX 5L (HACMP)
   • IBM Tivoli System Automation (TSA)
   • Sun Cluster
   • VERITAS Cluster Server

2. Non-IP cluster failover, such as WebSphere WLM and WebSphere HAManager

Usually, IP-based cluster failover is slower (one to five minutes), and non-IP cluster failover is very fast (instantaneous). Whereas the WebSphere V6 HAManager does not require extra software, most non-IP cluster failover still relies on cluster software such as HACMP, TSA, Sun Cluster, or VERITAS Cluster Software to provide the cluster information.

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