title: Determine when Akka Cluster PubSub will broadcast to peer nodes
body: <p>I'm trying to use the <code>DistributedPubSubExtension</code> to broadcast certain actor's existence/location to an akka cluster, but haven't found a reliable way to determine when those messages will actually be broadcast to the cluster.</p>
  
  <p>I initially used <code>SubscribeAck</code> as a signal that the channel was ready, but that message arrives without any regard of the node's status in the cluster.</p>
  
  <p>Next I used <code>MemberUp</code> and <code>CurrentClusterState</code> as a signal, but the messages still did not reach subscribers on other nodes.</p>
  
  <p>I still use <code>MemberUp</code> and <code>CurrentClusterState</code> as a signal to set up a <code>system.scheduler.scheduleOnce</code> to <code>Publish</code> my actors existence to the channel and that is finally being received by subscribers on other nodes. However, arbitrary <em>sleeps</em> seem like a sure-fire way to fail in the future, when the timing happens to be off.</p>
  
  <p>Is there a better indicator when I might actually reach other nodes with a <code>Publish</code> or do i need to roll my own discovery, such as manually calling a <em>discovery</em> actor at a known good path on each node as it comes up?</p>