M1 fw fw
| || Gossip Router || *similarly
+----+ || || configured
| | || || cluster
Ma Mb || ||
You can also view members (M*) as unique host. Only M1 has access to the outside world. Can Ma and Mb use the same channel as M1 did? And effectively send and receive messages in the outside world using the Router?
Here's a vertical view of my schema, hopefully a better view than the previous.