move code to src/test

* so that it compiles and tests pass
* fix some additional snip references in getting started

akka-docs/src/test/scala/docs/cluster/TransformationBackend.scala

@@ -0,0 +1,52 @@
+package scala.docs.cluster
+
+import language.postfixOps
+import scala.concurrent.duration._
+import akka.actor.Actor
+import akka.actor.ActorRef
+import akka.actor.ActorSystem
+import akka.actor.Props
+import akka.actor.RootActorPath
+import akka.cluster.Cluster
+import akka.cluster.ClusterEvent.CurrentClusterState
+import akka.cluster.ClusterEvent.MemberUp
+import akka.cluster.Member
+import akka.cluster.MemberStatus
+import com.typesafe.config.ConfigFactory
+
+//#backend
+class TransformationBackend extends Actor {
+
+  val cluster = Cluster(context.system)
+
+  // subscribe to cluster changes, MemberUp
+  // re-subscribe when restart
+  override def preStart(): Unit = cluster.subscribe(self, classOf[MemberUp])
+  override def postStop(): Unit = cluster.unsubscribe(self)
+
+  def receive = {
+    case TransformationJob(text) => sender() ! TransformationResult(text.toUpperCase)
+    case state: CurrentClusterState =>
+      state.members.filter(_.status == MemberStatus.Up) foreach register
+    case MemberUp(m) => register(m)
+  }
+
+  def register(member: Member): Unit =
+    if (member.hasRole("frontend"))
+      context.actorSelection(RootActorPath(member.address) / "user" / "frontend") !
+        BackendRegistration
+}
+//#backend
+
+object TransformationBackend {
+  def main(args: Array[String]): Unit = {
+    // Override the configuration of the port when specified as program argument
+    val port = if (args.isEmpty) "0" else args(0)
+    val config = ConfigFactory.parseString(s"akka.remote.netty.tcp.port=$port").
+      withFallback(ConfigFactory.parseString("akka.cluster.roles = [backend]")).
+      withFallback(ConfigFactory.load())
+
+    val system = ActorSystem("ClusterSystem", config)
+    system.actorOf(Props[TransformationBackend], name = "backend")
+  }
+}