Group Members
Each group has a unique group name, which identifies its members to the group service.
In each group, every member must be able to assume any role, according to its current ordinal. You can satisfy this requirement in a natural way if all the members are process instances of one application program, compiled from source code with identical functionality (though they may execute on different hardware and operating system platforms).
Member applications and the group service are all within the same realm, and usually run on host computers within a local area network.
The first member to join a group establishes heartbeat and timeout parameters for the entire group, based on the activation interval property that the first member supplies in the join call. For consistent behavior, ensure that all members of a group supply the same activation interval.
An application can join several groups. Nonetheless, an application must not join a group a second time, that is, if it is already a member of that group.