Quick and dirty load balancer

gistfile1.scala

trait Frontend {
  this: Core =>

  def config: Config
  val log = LoggerFactory.getLogger(getClass)

  def route(flow:Flow[HttpRequest, Future[HttpResponse], Unit]): Route = {
      path("dictionaries" / Segment / "suggestions"){ dictionaryId =>
        get{
          parameters("ngr"){ ngr =>
            ctx =>
                Source.single(ctx.request)
                  .via(flow)
                  .runWith(Sink.head)
                  .flatMap(r => ctx.complete(r))
        }
      }
    }
  }

  def start() = {
    val flow = Flow() { implicit b =>
      import akka.stream.scaladsl.FlowGraph.Implicits._

      val balance = b.add(Balance[HttpRequest](2))
      val merge = b.add(Merge[Future[HttpResponse]](2))

      val proxyTo51 = Flow[HttpRequest].map(_ =>
        Http().singleRequest(HttpRequest(uri = Uri("http://localhost:4051/dictionaries/hello/suggestions?ngr=hond")))
      )
      val proxyTo52 = Flow[HttpRequest].map(_ =>
        Http().singleRequest(HttpRequest(uri = Uri("http://localhost:4052/dictionaries/hello/suggestions?ngr=hond")))
      )

      balance ~> proxyTo51 ~> merge
      balance ~> proxyTo52 ~> merge

      (balance.in, merge.out)
    }

    Http().bind(
      interface = config.getString("frontend.interface"),
      port = config.getInt("frontend.port")
    ).to(Sink.foreach { conn =>
      log.info(s"Connection from ${conn.remoteAddress}")
      conn.flow.join(route(flow)).run()
    }).run()
  }
}