How do I force JGroups which node to make coordinator?

Currently there is no way to do this. Jgroups has spent considerable time making sure that the coordinator can be any of the nodes in a group. All tasks that maintain and monitor the health of the group membership list are shared among all of the members in the group to make sure that the coordinator duties do not affect the performance of the coordinator too much. The standard GMS (Group MembershipService) protocol stack class is what is responsible for the coordinator selection. Currently it is just the first host in the view list.

To get this behavior, you are going to have to implement your own protocol stack. Interestingly, I've been working on a protocol stack for Jgroups which implements approximately what you are asking for however it is not ready for prime time.

Others may have taken a whack at this issue however. I would recommend posting on the jgroups mailing list and asking the same question.