Code for 2.2. Spotlight: Cluster Node Roles

Backend.scala

class TransformationBackend extends Actor {
  val cluster = Cluster(context.system)

  override def preStart(): Unit =
    cluster.subscribe(self, classOf[MemberUp])
  override def postStop(): Unit =
    cluster.unsubscribe(self)

  def receive = {
    case state: CurrentClusterState ⇒
      state.members.filter(_.status == MemberStatus.Up) foreach register
    case MemberUp(m) ⇒ register(m)
    case job => //...
  }

  def register(member: Member): Unit =
    if (member.hasRole("front"))
      context.actorSelection(RootActorPath(member.address) /
          "user" / "frontend") ! BackendRegistration
}