Q:

Topic not created in PubSub Emulator

I an trying Google PubSub Java Client library with Google PubSub Emulator.
I am running the PubSub Emulator as a docker container.
I can access the Emulator from my local machine using url like
http://localhost:32805/v1/projects/<DUMMY_PROJECT_ID>/topics
http://localhost:32805/v1/projects/<DUMMY_PROJECT_ID>/subscriptions
Have created a topic using
http://localhost:32805/v1/projects/<DUMMY_PROJECT_ID>/topics/<DUMMY_TOPIC_NAME>
a subscription using
http://localhost:32805/v1/projects/<DUMMY_PROJECT_ID>/subscriptions/<DUMMY_SUBSCRIPTION_NAME>
can push msgs using
http://localhost:32805/v1/projects/<DUMMY_PROJECT_ID>/topics/<DUMMY_TOPIC_NAME>:publish
can pull msgs using
http://localhost:32805/v1/projects/<DUMMY_PROJECT_ID>/subscriptions/<DUMMY_SUBSCRIPTION_NAME>:pull
Java application is also running as a separate docker container and has following env vars set...
PUBSUB_EMULATOR_HOST --- localhost:32805

PUBSUB_PROJECT_ID --- <DUMMY_PROJECT_ID>

and the following code...
    String hostport = System.getenv("PUBSUB_EMULATOR_HOST");

    ManagedChannel channel = ManagedChannelBuilder.forTarget(hostport).usePlaintext().build();

    try {
        TransportChannelProvider channelProvider = FixedTransportChannelProvider
                .create(GrpcTransportChannel.create(channel));

        CredentialsProvider credentialsProvider = NoCredentialsProvider.create();

        // Set the channel and credentials provider when creating a `TopicAdminClient`.
        // Similarly for SubscriptionAdminClient
        TopicAdminClient topicClient = TopicAdminClient.create(TopicAdminSettings.newBuilder()
                .setTransportChannelProvider(channelProvider).setCredentialsProvider(credentialsProvider).build());

        TopicName topicName = TopicName.of(projectID, "niks-test-01");

        topicClient.createTopic(topicName);

        // Set the channel and credentials provider when creating a `Publisher`.
        // Similarly for Subscriber
        Publisher publisher = Publisher.newBuilder(topicName).setChannelProvider(channelProvider)
                .setCredentialsProvider(credentialsProvider).build();
    } catch (Exception e) {
        System.out.println(e.getMessage());
    } finally {
        channel.shutdown();
    }

Application is up and the above code also executes successfully but when I query the topic
using http://localhost:32805/v1/projects/<DUMMY_PROJECT_ID>/topics it returns nothing...
After printing lot of logs I see that app is stuck @ topicClient.createTopic(topicName); no further logs or exceptions...
Any idea whats wrong here... Thanks...
Edit#1: Found that it is less of an emulator issue but more of a docker issue... Containers r not able to talk using localhost...

A:

As found during my initial investigation, it was not an application issue but more of a docker issue.
During further investigation I found that containers might not be using same network.
So I created a network with
docker network create test-network
and then
docker run --network=test-network -itd --name=pubsub-emulator <IMAGE_NAME>
&
docker run --network=test-network -itd --name=pubsub-app <IMAGE_NAME> -e PUBSUB_EMULATOR_HOST=pubsub-emulator:<INTERNAL_PORT
Now the app is able to communicate with the pubsub-emulator...

