public class TransformationFrontend extends UntypedActor {
  List<ActorRef> backends = new ArrayList<ActorRef>();
  int jobCounter = 0;
  @Override
  public void onReceive(Object message) {
    if ((message instanceof TransformationJob) && backends.isEmpty()) {
      TransformationJob job = (TransformationJob) message;
 
      getSender().tell(
          new JobFailed("Service unavailable, try again later", job),
          getSender());
    } else if (message instanceof TransformationJob) {
      TransformationJob job = (TransformationJob) message;
      jobCounter++;
      backends.get(jobCounter % backends.size())
 
          .forward(job, getContext());
    } else if (message.equals(BACKEND_REGISTRATION)) {
      getContext().watch(getSender());
      backends.add(getSender());
    } else if (message instanceof Terminated) {
      Terminated terminated = (Terminated) message;
      backends.remove(terminated.getActor());
 
    } else {
      unhandled(message);
    }
  }
}