Akka distributed pub sub: Java implementation not working

Question

Main class for Subscriber: Application.java

package com.mynamespace;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.ComponentScan;

import akka.actor.ActorRef;
import akka.actor.ActorSystem;
import akka.actor.Props;
import akka.contrib.pattern.DistributedPubSubExtension;
import akka.contrib.pattern.DistributedPubSubMediator;

import com.mynamespace.actors.SubscriberActor;

@SpringBootApplication
@ComponentScan(basePackages = "com.mynamespace.*")   
public class Application {

    public static void main(String[] args) throws InterruptedException {

        ApplicationContext ctx = SpringApplication.run(Application.class, args);
        // get hold of the actor system
        ActorSystem system = ctx.getBean(ActorSystem.class);
        ActorRef mediator = DistributedPubSubExtension.get(system).mediator();
        ActorRef subscriber = system.actorOf(
                Props.create(SubscriberActor.class), "subscriber");
       // subscribe to the topic named "content"
        mediator.tell(new DistributedPubSubMediator.Put(subscriber), subscriber);
        // subscriber.tell("init", null);
        System.out.println("Running.");
        Thread.sleep(5000l);
    }
}

Subscriber actor: SubscriberActor.java

package com.mynamespace.actors;

import java.util.ArrayList;
import java.util.List;

import akka.actor.UntypedActor;

import com.mynamespace.message.CategoryServiceRequest;
import com.mynamespace.message.CategoryServiceResponse;

public class SubscriberActor extends UntypedActor {

    @Override
    public void onReceive(Object msg) throws Exception {
        if (msg instanceof CategoryServiceRequest) {
            System.out.println("Request received for GetCategories.");
            CategoryServiceResponse response = new CategoryServiceResponse();
            List<String> categories = new ArrayList<>();
            categories.add("Food");
            categories.add("Fruits");
            response.setCatgories(categories);
            getSender().tell(response, getSelf());
        } else if (msg instanceof String && msg.equals("init")) {
            System.out.println("init called");
        } else {
            System.out
                .println("Unhandelled message received for getCategories.");
        }
    }

}

Application.conf for subscriber

akka {
    loglevel = INFO
    stdout-loglevel = INFO
    loggers = ["akka.event.slf4j.Slf4jLogger"]
    extensions = ["akka.contrib.pattern.DistributedPubSubExtension"]
    actor {
      provider = "akka.cluster.ClusterActorRefProvider"
    }

    remote {
       enabled-transports = ["akka.remote.netty.tcp"]
       netty.tcp {
         hostname = "127.0.0.1"
         port = 0
       }
     }

     cluster {
    seed-nodes = [
      "akka.tcp://mynamespace-actor-system@127.0.0.1:2551",
      "akka.tcp://mynamespace-actor-system@127.0.0.1:2552"]

    auto-down-unreachable-after = 10s
    }

}

Main class for publisher: Application.java

package com.mynamespace;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.ComponentScan;

import akka.actor.ActorRef;
import akka.actor.ActorSystem;
import akka.actor.Props;
import akka.contrib.pattern.DistributedPubSubExtension;
import akka.contrib.pattern.DistributedPubSubMediator;

import com.mynamespace.actors.PublisherActor;

@SpringBootApplication
@ComponentScan(basePackages = "com.mynamespace.*")
public class Application {

    public static void main(String[] args) throws InterruptedException {

        ApplicationContext ctx = SpringApplication.run(Application.class, args);
        // get hold of the actor system
        ActorSystem system = ctx.getBean(ActorSystem.class);
        ActorRef mediator = DistributedPubSubExtension.get(system).mediator();
        ActorRef publisher = system.actorOf(Props.create(PublisherActor.class),
            "publisher");
        mediator.tell(new DistributedPubSubMediator.Put(publisher), publisher);
        Thread.sleep(5000);
        publisher.tell("hi", publisher);
        System.out.println("Running.");
    }
}

PublisherActor.java

package com.mynamespace.actors;

import scala.concurrent.Future;
import akka.actor.ActorRef;
import akka.actor.UntypedActor;
import akka.contrib.pattern.DistributedPubSubExtension;
import akka.contrib.pattern.DistributedPubSubMediator;
import akka.dispatch.Mapper;
import akka.pattern.Patterns;
import akka.util.Timeout;

import com.mynamespace.message.CategoryServiceRequest;
import com.mynamespace.message.CategoryServiceResponse;

public class PublisherActor extends UntypedActor {

    // activate the extension
    ActorRef mediator = DistributedPubSubExtension.get(getContext().system())
        .mediator();

    public void onReceive(Object msg) {
        if (msg instanceof String) {
            Timeout timeOut = new Timeout(50000l);
            mediator.tell(new DistributedPubSubMediator.Send(
                    "/user/subscriber", new CategoryServiceRequest()),
                    getSelf());
            Future<Object> response = Patterns.ask(mediator,
                    new DistributedPubSubMediator.Send("/user/subscriber",
                            new CategoryServiceRequest()), timeOut);
            Future<CategoryServiceResponse> finalresponse = response.map(
                    new Mapper<Object, CategoryServiceResponse>() {

                        @Override
                        public CategoryServiceResponse apply(Object parameter) {
                            CategoryServiceResponse responseFromRemote = (CategoryServiceResponse) parameter;
                            System.out.println("received:: list of size:: "
                                + responseFromRemote.getCatgories().size());
                            return responseFromRemote;
                        }

                    }, getContext().system().dispatcher());
        } else if (msg instanceof DistributedPubSubMediator.SubscribeAck) {
            System.out.println("subscribbed.......");

        } else {
            unhandled(msg);
        }
    }
}

Application conf for publisher is same as of subscriber. Both are running on different ports on the same system.

I have two seed nodes defined and running on my local system. Somehow I am not able to ASK/TELL subscriber from producer (both running on different nodes) via DistributedPubSub Mediator.

After running Subscriber then publisher: I don't get any exceptions or any dead letter references printed in stdout/logs.

Is it possible to be able to view what actor references my mediator holds?

Need help to find issues or possible issues.

One thing you might want to try is to upgrade akka to 2.4.0-RC2 on which the PubSub pattern got into the akka-cluster-tools module. I'm using this on both Java and Scala with similar pattern as yours and it works nicely. Corresponding versioned official doc: http://doc.akka.io/docs/akka/2.4.0-RC2/java/distributed-pub-sub.html — waterscar, Sep 10 '15 at 07:59
I am having exactly (Spring Boot + Akka) same problem. Using Akka v2.4.17. Publish/Subscribe works fine, Put/Send does not (subscruber after Put does not receive SubscribeAck), used samples from http://doc.akka.io/docs/akka/current/java/distributed-pub-sub.html#distributed-pub-sub-send-java — spam, Feb 24 '17 at 22:39
@spam: I have the exact same problem. Did you manage to solve it? I'm running out of ideas, I think i'll have to debug the scala code to see what's up, and as you pointed out, the problem most likely is on the subscriber that never gets that SubscribeAck. Any pointers will be very helpful — João Antunes, Aug 08 '17 at 10:03
@spam: I ended up using the Publisher Subscribe with groups and 'send only one to group' option on. Works as a charm! (thanks still, your comment telling me that the Publish worked was helpful) — João Antunes, Aug 08 '17 at 10:50

score 0 · Answer 1 · answered Aug 08 '17 at 10:53

I had the same problem, after the comments from @spam and my own experiments the thing I can recommend is to use Publish/Subscribe with groups and sendOneMessageToEachGroup=true.

Is it supposed that the Send only works locally? if so the documentation doesn't explicit that. But I can also tell by the code there that this specific part of the documentation has been overlooked apparently (as change the Class names but then don't invoke those, invoke the previous ones on the previous examples)

Hope this helps anyone that has this issue, as the docs are a bit misleading apparently

Akka distributed pub sub: Java implementation not working

1 Answers1