Error in graph create: requirement failed: The inlets [] and outlets [] must correspond to the inlets [in] and outlets [out]

Question

I'm using akka streams graphDSL to create a runnable graph. There are no compile-time errors wrt inlet / outlet of the stream components. Runtime throws following error:

Any ideas what should I verify to make it run ?

requirement failed: The inlets [] and outlets [] must correspond to the inlets [in] and outlets [out]
at scala.Predef$.require(Predef.scala:219)
at akka.stream.Shape.requireSamePortsAs(Shape.scala:168)
at akka.stream.impl.StreamLayout$CompositeModule.replaceShape(StreamLayout.scala:390)
at akka.stream.scaladsl.GraphApply$class.create(GraphApply.scala:18)
at akka.stream.scaladsl.GraphDSL$.create(Graph.scala:813)
at com.flipkart.connekt.busybees.streams.Topology$.bootstrap(Topology.scala:109)
at com.flipkart.connekt.busybees.BusyBeesBoot$.start(BusyBeesBoot.scala:65)
at com.flipkart.connekt.boot.Boot$.delayedEndpoint$com$flipkart$connekt$boot$Boot$1(Boot.scala:39)
at com.flipkart.connekt.boot.Boot$delayedInit$body.apply(Boot.scala:13)

The graph structure:

source ~> flowRate ~> render ~> platformPartition.in
platformPartition.out(0) ~> formatIOS ~> apnsDispatcher ~> apnsEventCreator ~> merger.in(0)
platformPartition.out(1) ~> formatAndroid ~> httpDispatcher ~> gcmPoolFlow ~> rHandlerGCM ~> merger.in(1)
merger.out ~> evtCreator ~> Sink.ignore

Answer 1

You have an unused inlet or outlet (one of your flows or something isn't connected on all sides). Here are some examples:

This works:

val workingFlow =
  Flow.fromGraph(GraphDSL.create() { implicit b =>
    import GraphDSL.Implicits._
    val intFlow = b.add(Flow[Int])
    FlowShape(intFlow.in, intFlow.out)
  })

The following code produces an error similar to yours, because it has an entire unused flow:

val buggyFlow =
  Flow.fromGraph(GraphDSL.create() { implicit b =>
    import GraphDSL.Implicits._
    val intFlow = b.add(Flow[Int])
    val unusedFlow = b.add(Flow[Int]) // ERROR: This flow is unused
    FlowShape(intFlow.in, intFlow.out)
  })

A slightly more complex example: Here there isn't an entire unused flow, there's just an unused outlet. It produces the same error:

val buggyFlow =
  Flow.fromGraph(GraphDSL.create() { implicit b =>
    import GraphDSL.Implicits._

    val broadcast = b.add(Broadcast[Int](2))
    val intFlow = b.add(Flow[Int])
    val unusedFlow = b.add(Flow[Int]) // ERROR: This flow's outlet isn't used

    broadcast ~> intFlow
    broadcast ~> unusedFlow

    FlowShape(broadcast.in, intFlow.out)
  })