Router.scala

class Router(routeeProps: Props, parallelism: Int) extends Actor with ActorLogging {

  private def partitionCampaign(cid: String): Int = {
    val rawMod = cid.hashCode % parallelism
    rawMod + (if (rawMod < 0) parallelism else 0)
  }

  override def receive: Receive = initialized(ListMap.empty[Int, ActorRef])

  def initialized(routees: Map[Int, ActorRef]): Receive = {
    case cacheCmd: CacheCmd =>
      val partition = partitionCampaign(cacheCmd.cid)
      val (newRoutees, updated) = routees.updateIfMissing(partition)(context.actorOf(routeeProps))
      newRoutees(partition).tell(cacheCmd, sender())
      if (updated)
        context.become(initialized(newRoutees))
  }
}