Spring Boot cloud GCP cannot connect to local Google PubSub emulator

Question

Trying to connect to local Google PubSub emulator from Spring boot application for tests.

Using below config
spring.cloud.gcp.pubsub.emulator-host=localhost:8085

Started emulator in local successfully on 8085, Also have set PUBSUB_EMULATOR_HOST=localhost:8085

Note: While connecting to the actual Google PubSub topic everything just works fine.

Answer 1

When using the Pub/Sub emulator, use the FixedTransportChannelProvider and NoCredentialsProvider to create a Publisher or Subscriber . This is demonstrated in UsePubSubEmulatorSnippet.java :

String hostport = System.getenv("PUBSUB_EMULATOR_HOST");
ManagedChannel channel = ManagedChannelBuilder.forTarget(hostport).usePlaintext(true).build();
TransportChannelProvider channelProvider = FixedTransportChannelProvider.create(GrpcTransportChannel.create(channel));

CredentialsProvider credentialsProvider = NoCredentialsProvider.create();

ProjectTopicName topicName = ...

// Use the channel and credentials provider when creating a Publisher or Subscriber.
Publisher publisher =
    Publisher.newBuilder(topicName)
        .setChannelProvider(channelProvider)
        .setCredentialsProvider(credentialsProvider)
        .build();

Answer 2

1. Create a file under src/test/resources/application.properties
2. Set spring.cloud.gcp.pubsub.emulator-host=localhost:8085 inside the test application.properties.
3. Annotate your test class so that Spring picks up your test application.properties:

@RunWith(SpringRunner::class)
@SpringBootTest

EDIT: I created an example project that shows how to use Spring with PubSub emulator in a test (which also requires creating the topic and subscription): https://github.com/nhartner/pubsub-emulator-demo

Answer 3

We can use Testcontainers approach for using all the supported services. It provides you with a docker container where the emulators would be running and help to use different configurations for multiple projects and update test setup as per the individual test case. For pubsub, please use the below configuration you can create the initial setup: ie topics and subscriptions

companion object {
    private val log = logger(GCPSetup::class.java)
    private val emulator: PubSubEmulatorContainer = PubSubEmulatorContainer(
        DockerImageName.parse("gcr.io/google.com/cloudsdktool/cloud-sdk:316.0.0-emulators")
    )

    init {
        emulator.start()
    }

    @Configuration
    class EmulatorConfiguration{
        @Bean
        fun credentialProvider() = NoCredentialsProvider()
    }
    @DynamicPropertySource
    fun emulatorProperties(registry:DynamicPropertyRegistry){
        registry.add("spring.cloud.gcp.pubsub.emulator-host") { emulator.emulatorEndpoint }
    }
}

The above example is in Kotlin, but you can use the above configuration in static block in java.