   Cluster cluster = Cluster.get(getContext().getSystem());    //subscribe to cluster changes   @Override   public void preStart() {     cluster.subscribe(getSelf(), ClusterEvent.initialStateAsEvents(),          MemberEvent.class, UnreachableMember.class);   }    //re-subscribe when restart   @Override   public void postStop() {     cluster.unsubscribe(getSelf());   }    @Override   public Receive createReceive() {     return receiveBuilder()       .match(