@Override
    public void memberJoined(DistributionManager distributionManager,
        InternalDistributedMember id) {
      if (!agent.isListening()) {
        return;
      }
      synchronized (this) {
        if (!distributedMembers.contains(id)) {
          distributedMembers.add(id);
          agent.addPendingJoin(id);
          agent.joinProcessor.resumeHandling();
        }
      }
    }
This method is invoked when a new member joins the system. If the member is an application VM
or a GemFire system manager, we note it.

@see JoinLeaveListener#nodeJoined
geode-core/src/main/java/org/apache/geode/internal/admin/remote/RemoteGfManagerAgent.java