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When people talk about clustering, they often mean different things. The reason is that there are two kinds of cluster failovers:
This approach deals with a Virtual IP Address or IP Alias. The IP Alias is only used for one system at a time. In case of a failover, the IP Alias is moved to the other system. All applications or services have to use the Virtual IP Address to access the cluster.
examples for software using this approach are IBM HACMP, TSA, Sun Cluster, VeRITAS Cluster Server.
In this case, there is a process failover, regardless of the TCP/IP connection parameter. Such a failover is provided by an application or a vendor specific protocol.
For example, WebSphere workload management (WLM) and the WebSphere HAManager use this approach.
Usually, IP-based cluster failover is slower (one to five minutes), and non-IP cluster failover is very fast (instantaneous). While the WebSphere V6 HAManager does not require extra software, most non-IP cluster failover still relies on external cluster software to provide the cluster information.
