[Pacemaker] virtual IP or real IP address

[gilberto migliavacca]

Hi

I have a question. I've seen in the mailing list
a lot of example with the IPAddr/IPAddr2 resource agent

this resource agent manages the Virtual IP.

Could anybody explain me why I have to create a
virtual IP istead of using the real IP?

for instance

I have a cluster with 2 nodes and 1 tomcat on both
machines
My purpose is just to start and stop (maybe configure)
these tomcat instances.

I've created a configuration with the IPsrcaddr resource
agent I think this should manage the real IP, isn't it?

Could anybody point me in the right direction?

thanks in advance

gilberto