title: how to configure a Akka Pub/Sub to run on same machine?
body: <p>I am following the Distributed Publish Subscribe in Cluster example in Akka. However, I would like to run all the actor (publisher and subscribers) on the same node (my laptop). I am not sure if I understand how to configure that, could somebody help me? is it possible to use the runOn or should it be declared in a configuration file? Currently, 
  I run into this error:</p>
  
  <pre><code>Caused by: akka.ConfigurationException: ActorSystem [akka://mySystem] 
  needs to have a 'ClusterActorRefProvider' enabled in the 
  configuration, currently uses [akka.actor.LocalActorRefProvider]
  </code></pre>