Connecting to NATS cluster (pub/sub) not working

Hello,

I’ve integrated NATS Java in my project, and it’s all working fine when using a single NATS instance, but it’s not working when I’m using NATS Java with a cluster. I’ve ended up writing the simplest possible code. Please check this simple code:

public class NatsSimpleClusterExample {
  public NatsSimpleClusterExample() {
  String[] servers = new String[] {
        "nats://localhost:7244",
        "nats://localhost:7245",
        "nats://localhost:7246"
    };

    Runnable consumer = () -> {
      ConnectionFactory cf = new ConnectionFactory();
      cf.setServers(servers);

      try {
        Connection nc = cf.createConnection();
        System.out.println("Consumer connected to: " + nc.getConnectedUrl());
        nc.subscribe("TEST", m -> System.out.println(new String(m.getData())));
      } catch (Exception e) {
        System.out.println(e.getMessage());
      }
    };

    new Thread(consumer).start();

    Runnable producer = () -> {
      ConnectionFactory cf = new ConnectionFactory();
      cf.setServers(servers);
      try {
        Connection nc = cf.createConnection();
        System.out.println("Producer connected to: " + nc.getConnectedUrl());
        long i = 0;
        while (true) {
          nc.publish("TEST", String.valueOf(i).getBytes());
          if (i % 1000000 == 0) {
            System.out.println("Published: " + i + " elements...");
          }
          i++;
        }
      } catch (Exception e) {
        System.out.println(e.getMessage());
      }
    };

    new Thread(producer).start();
  }

  public static void main(String[] args) {
    new NatsSimpleClusterExample();
  }
}

Result being:

Consumer connected to: nats://localhost:7246
Producer connected to: nats://localhost:7245
Published: 0 elements...
Published: 1000000 elements...
Published: 2000000 elements...
Published: 3000000 elements...
Published: 4000000 elements...
Published: 5000000 elements...
Published: 6000000 elements...

So the producer IS producing data, but the consumer IS NOT subscribing to it? Am I missing something here? My NATS instances are running and all looks good.

Thanks in advance for your help!

[kozlovic]

@magdkudama If your test program is as described above, you are setting the server URLs to:

String[] servers = new String[] {
        "nats://localhost:7244",
        "nats://localhost:7245",
        "nats://localhost:7246"
    };

These are the ROUTE listen ports, not the clients, which based on your config files are 4222, 4223 and 4224.

Furthermore, since you are using 2 connections for subscribe and publish and running the subscriber first but in a thread, you should make sure that the subscription has reached the server before starting publishing (if you don’t want to miss ANY message). If that’s the case, you should do a nc.flush() after the nc.subscribe() call and notify the main thread that you reached that point before starting the publisher thread.

[magdkudama]

That sounds good, thanks both for your help.