Hi Ravi,
When you are saying FlipFlop that means active / passive? and it is expected that the fundamental solution to make the change? if this is the case, In this redbook you have some examples:
WebSphere Application Server Network Deployment V6: High Availability Solutions
www.redbooks.ibm.com/abstracts/sg246688.... I have work with HACMP and the solution works very, very fine (with WAS and with Message Broker).
I have work with Linux HA Cluster product called Poliserver with Portal Server and the same. As i know Red Hat Enterprise version can implement OS Cluster.
In Windows you can do with Microsoft Cluster (i have see for clusters of FileNet)
Sure that in virtualize environments there are more solutions.
Hope this helps,
regards,