Broadcast messages are not working in a cluster?

[Eugene Dzhurinsky]

I'm trying to create a simple proof of concept for working with a group of actors in a cluster.

I've created the following example 

https://gist.github.com/jdevelop/b57c9b1b0e0063b4ccc1

the problem is - sending a Broadcast message to a consistent-hashing-group router, obtained from the cluster configuration - seems to send a message only to a single routee - not all of them.

The sample output from the code above:

Started akka://Test/user/routeeA/$h
Started akka://Test/user/routeeA/$i
Started akka://Test/user/routeeA/$f
Started akka://Test/user/routeeA/$j
Started akka://Test/user/routeeA/$a
Started akka://Test/user/routeeA/$g
Started akka://Test/user/routeeA/$b
Started akka://Test/user/routeeA/$c
Started akka://Test/user/routeeA/$e
Started akka://Test/user/routeeA/$d
Started akka://Test/user/splitter/$b
Started akka://Test/user/splitter/$a
Received data to process
Broadcasting work for akka://Test/user/routerA
Received broadcast from akka.tcp://Te...@127.0.0.1:2552/user/splitter/$a
Worker Actor[akka.tcp://Te...@127.0.0.1:2551/user/routeeA/$a#410953742] wants some data
Process to respond akka.tcp://Te...@127.0.0.1:2552/user/splitter/$a
Worker Actor[akka.tcp://Te...@127.0.0.1:2551/user/routeeA/$a#410953742] completes its job

As it is seen - the only one actor receives the broadcast message - not 10, which is weird.

Can you please advice how to fix that (without using DistributedPubSubMediator)?

Thank you!

[Eugene Dzhurinsky]

I have changed the line

router ! Broadcast(WhosOnDuty)

into 

router ! ConsistentHashableEnvelope(Broadcast(WhosOnDuty), WhosOnDuty)

And that solved the issue. So it seems the cluster-aware router "unwraps" the Broadcast message and then passes it to the, thus using the "normal" delivery mode for the given route.

Interestingly, the code

router ! Broadcast(Broadcast(WhosOnDuty))

works as expected too - so the message is being sent to all routees.

I don't know if it's an expected behavior, but seems to be quite surprising for me.

[Dmitry Semenov]

Not sure if it relative to the problem you want to solve, but you can do following stuff to get all routees

def guardianReceive: Actor.Receive = {
  case DiscoverChildren ⇒
    router ! GetRoutees
  case Routees(routees) =>
    routees.foreach {
      case ActorRefRoutee(ref) => addWorker(ref)
        ref ! GuardianRegistration
    }
}

[Patrik Nordwall]

Hi Eugene,

That should be fixed. I have created an issue.

https://github.com/akka/akka/issues/16611

Thanks for reporting.

/Patrik

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[Assaf Abulafia]

Hi,

any idea if that issue ended up in akka 2.4?

I'm stumbling upon something similar, not sure if this is the same bug or not,

when sending a Broadcast to all actors behind a consistent hashing router, I get the following error (where MyMessage is the broadcast's payload)

a.routing.ConsistentHashingRoutingLogic  : Message [MyMessage] must be handled by hashMapping, or implement [akka.routing.ConsistentHashingRouter$ConsistentHashable] or be wrapped in [akka.routing.ConsistentHashingRouter$ConsistentHashableEnvelope]

thanks,

Assaf