Primary/Secondary(hot-standby) fail over cluster setup

Hi,

Any one has an idea on how to setup Primary/Secondary(hot-standby)weblogic cluster for hot fail over?
i.e. Node A and Node B should be up and running. All the request should go only to Node A;
If Node A is not available, all the request should go to Node B.

We want to do this only with weblogic proxy plug-in.
(external H/W load balancer is not an option for us)

In IBM websphere, it is pretty easy to do by marking primary and secondary server nodes in the plug-in config file but I could not find anything equivalent in weblogic world.

can anyone throw some light ?

-Thanks.