We already have seen how WebLogic can replicate server-side session-state information to a secondary server, thereby enabling WebLogic to reconstruct the session state on the secondary server in the event of a failure. In order to guarantee high availability, it is sensible to ensure that WebLogic chooses the secondary server from one of the servers running on a different physical machine. By doing this, if a machine hosting multiple WebLogic instances fails, their secondary servers will run on different hardware and not be affected by the crash.
You can specify the set of servers in the cluster that should be considered for holding the replicated session state by assigning machine names to WebLogic instances. You can refine this scheme further by setting up replication groups. A replication group is just a list of preferred servers within the cluster that should be used as secondary servers.
To set up a new machine, click the Machines node in the left pane of the Administration Console, and select the "Configure a new Machine" option. Chapter 13 shows how the Node Manager configuration uses these machine definitions.
A machine name is a tag that can be associated with a number of WebLogic instances. By making these associations, you indicate which servers are running on which machines. WebLogic's clustering framework can use this information to determine the preferred secondary server. By default, the secondary server is ...