akka http: Server Binding not behaving as expected

Question

I have following code:

val serverSource = Http().bind("localhost", 8080)
val connectionSink = Sink.foreach[IncomingConnection] {
    connection => println(s"Accepted incoming connection from ${connection.remoteAddress}")
  }
val serverBindingFuture = serverSource.to(connectionSink).run()
serverBindingFuture.onComplete {
    case Success(binding) => {
      println("Server binding successful")
      binding.terminate(10 seconds)
    }
    case Failure(ex) => println(s"Server binding failed $ex")
}

As the snippet tells, I am terminating the server binding after 10 seconds. So I expect that if I send the request before this period expires, I should get message 'Accepted incoming connection from...' printed.

But I observe that I always get 'This site can’t be reached', and message is never printed.

Alec Alec · Accepted Answer · 2020-04-28T13:36:49

As the snippet tells, I am terminating the server binding after 10 seconds. So I expect that if I send the request before this period expires, I should get message 'Accepted incoming connection from...' printed.

You've misunderstood the semantics of terminate. The duration argument is a hard deadline for shutdown, not an indication that the server will continue accepting requests until then.

Here's a tweak to your code to demonstrate this.

print Server binding successful as soon as the server is up and wait 10 seconds before calling terminate
print Starting shutdown right before calling terminate and print Finished shutdown as soon as the terminate completes

You should see:

curl 'http://localhost:8080/api triggers the println until Starting shutdown appears
the delay between Starting shutdown and Finished shutdown is likely to be quite short (much shorter that 10 seconds)

val serverSource = Http().bind("localhost", 8080)
val connectionSink = Sink.foreach[IncomingConnection] {
  connection => println(s"Accepted incoming connection from ${connection.remoteAddress}")
}
val serverBindingFuture = serverSource.to(connectionSink).run()
serverBindingFuture.onComplete {
  case Success(binding) => {
    println("Server binding successful")
    system.scheduler.scheduleOnce(10 seconds) {
      println("Starting shutdown")
      binding.terminate(10 seconds).onComplete { termOutcome =>
        println(s"Finished shutdown $termOutcome")
      }
    }
  }
  case Failure(ex) => println(s"Server binding failed $ex")
}

akka http: Server Binding not behaving as expected

1 Answers