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/TransformationFrontend.scala

@@ -0,0 +1,60 @@
+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.Terminated
+import akka.pattern.ask
+import akka.util.Timeout
+import com.typesafe.config.ConfigFactory
+import java.util.concurrent.atomic.AtomicInteger
+
+//#frontend
+class TransformationFrontend extends Actor {
+
+  var backends = IndexedSeq.empty[ActorRef]
+  var jobCounter = 0
+
+  def receive = {
+    case job: TransformationJob if backends.isEmpty =>
+      sender() ! JobFailed("Service unavailable, try again later", job)
+
+    case job: TransformationJob =>
+      jobCounter += 1
+      backends(jobCounter % backends.size) forward job
+
+    case BackendRegistration if !backends.contains(sender()) =>
+      context watch sender()
+      backends = backends :+ sender()
+
+    case Terminated(a) =>
+      backends = backends.filterNot(_ == a)
+  }
+}
+//#frontend
+
+object TransformationFrontend {
+  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 = [frontend]")).
+      withFallback(ConfigFactory.load())
+
+    val system = ActorSystem("ClusterSystem", config)
+    val frontend = system.actorOf(Props[TransformationFrontend], name = "frontend")
+
+    val counter = new AtomicInteger
+    import system.dispatcher
+    system.scheduler.schedule(2.seconds, 2.seconds) {
+      implicit val timeout = Timeout(5 seconds)
+      (frontend ? TransformationJob("hello-" + counter.incrementAndGet())) onSuccess {
+        case result => println(result)
+      }
+    }
+
+  }
+}