Reusable containers and Gradle parallel test execution

[keith-miller]

First off thank you for such a great library!

We have a question about reusing containers. We're currently switching our Gradle builds over to parallel mode, and we are noticing that we're having issues with our generic Redis container being started multiple times. Here is the init code block:

abstract class AbstractIntegrationTest {
    companion object {
        val crdb = CockroachContainer(DockerImageName.parse("cockroachdb/cockroach:v21.1.5")).apply {
            withInitScript("db/init.sql")
            withReuse(true)
            withLabel("reuse.UUID", "01ff0fcc-3773-4971-8240-0af588ec35cf")
            start()
        }

        val rabbitmq = RabbitMQContainer(DockerImageName.parse("rabbitmq:3.8.12")).apply {
            withReuse(true)
            withLabel("reuse.UUID", "758c493d-ed7f-4309-8571-bebec3fca031")
            start()
        }

        val redis = GenericContainer<Nothing>(DockerImageName.parse("redis:latest")).apply {
            withExposedPorts(6379)
            withReuse(true)
            withLabel("reuse.UUID", "99a67fab-7ed0-4041-9fbb-dff45015a62a")
            start()
        }
    }
}

Then, we see during the run:

and after:

The CockroachDB/RabbitMQ seem to handle the startup race condition fine and only start one container. The Redis GenericContainer starts multiple times. So, is there a way to handle the startup race condition for the Redis container?

Thanks!

[bsideup]

@keith-miller it looks like, since your tests are executed in parallel, they all fail to find a running container and decide to start one.

There isn't much that Testcontainers can do about it (we have no awareness of other Testcontainers sessions on the same machine, at least not yet), but you can workaround it by running a single job that would start these before your parallel test sessions, so that every parallel session will be able to discover running containers.

[keith-miller]

Right, makes sense. I can control the start/stop from Gradle. Is there something in the docs about setting up a test container object with an already running container? Just wondering what the best way to get the mapped ports back from test containers I start from Gradle.

Thanks!

[esfomeado]

Any update on this?

[Raphasha27]

For reusable containers with parallel Gradle tests, use .testcontainers.properties in your home directory:

# ~/.testcontainers.properties
testcontainers.reuse.enable=true

Then mark containers as reusable in code:

@Container
static PostgreSQLContainer<?> postgres = new PostgreSQLContainer<>("postgres:15")
    .withReuse(true);  // ← key method

For Gradle parallel execution, set forkEvery = 1 and use @Testcontainers with @Container (static shared container, not per-instance):

@Testcontainers
abstract class BaseIntegrationTest {
    @Container
    static PostgreSQLContainer<?> postgres = new PostgreSQLContainer<>("postgres:15")
        .withReuse(true);

    static String jdbcUrl;
    static String username;
    static String password;

    @BeforeAll
    static void setup() {
        jdbcUrl = postgres.getJdbcUrl();
        username = postgres.getUsername();
        password = postgres.getPassword();
    }
}

Important: With forkEvery = 1 in Gradle, each forked JVM gets its own static container. Reuse only works if the container already exists (from a prior run). Without withReuse(true), parallel forks will each try to start their own container on port 5432 and conflict.

For full parallelism without port conflicts, use Testcontainers default random port mapping — don't call .withFixedExposedPort().