When a node is brought online, it uses multicast discovery to learn about other nodes. You can see the gist here: https://github.com/nanopack/mist/blob/master/main.go#L68-L76

Propagating events is really simple: When a client subscribes to a particular node, the node will replicate the subscription to all nodes in the cluster, and relay any messages from the 'proxied' subscriptions back to the client.