Integrating Play Framework 2.6 with gRPC and Netty

Question

At the time I write this post, Play Framework is at v2.6.0-M4. The v2.5 version of the framework had difficulties to work with gRPC because of Netty conflicts (see this stackoverflow answer).

I'm starting to look into gRPC and protobufs. Already ported a project from Play Framework 2.5 > 2.6.0-M4 in anticipation of the actual release. Currently I have some questions regarding integration of gRPC. I'm wondering how to let the gRPC server work along nicely with Play Framework. I know that v2.6 switched to Akka HTTP server instead of Netty, while I use the grpc-netty dependency in sbt so maybe I'll have to switch the project to Netty again (here's how).

For testing purposes, I created a quick and dirty GrpcServer.scala class that starts up a thread with the GrpcServer listening. I managed to add ScalaPB with gRPC and generate/compile my protobufs. It works perfectly to communicate with a small testing NodeJS app but I have to startup this server app independently from the main project:

private def start(): Unit = {
    server = ServerBuilder.forPort(GrpcServer.port).addService(GreeterGrpc.bindService(new GreeterImpl, executionContext)).build.start
    GrpcServer.logger.info("Server started, listening on " + GrpcServer.port)
    sys.addShutdownHook {
        System.err.println("*** shutting down gRPC server")
        self.stop()
        System.err.println("*** server shut down")
    }
}

Possible solutions to integrate gRPC in Play Framework

Now for the real integration in Play Framework v2.6, I'm looking for suggestions. Here's some things I can do:

• Create a module and start the gRPC server when Play Framework starts up, like described in this stackoverflow answer. This would mean that we run the gRPC server on a different port next to the existing server (Akka HTTP server from Play Framework 2.6)
• Create a Scala Command and make it long-running. So we always make sure we start a command that runs the gRPC server when we start our application on a server.
• Switch from Akka HTTP to Netty in Play Framework v2.6 and tightly integrate gRPC with the existing Netty server so it hooks into the existing Netty server instead of creating a server on our own. I would like this solution but not sure how to deal with it. It certainly would avoid having two separate http stacks running.

Any tips/ideas for a clean integration are helpful as there's not much information about Play Framework and gRPC available, except that there were issues in the previous 2.5 version...