Port mapping for ipv4 & ipv6 can cause different ports to be mapped and getMappedPort function will return wrong port

[vsamofal]

Expected Behaviour

I want to get a predictable port number and host,

the problem seems to be in this file - https://github.com/testcontainers/testcontainers-node/blob/main/packages/testcontainers/src/utils/bound-ports.ts

method - resolveHostPortBinding
line - return hostPortBindings[0].hostPort;

Actual Behaviour

We have tests that are running in parallel and it was quite hard to identify that issue, because locally on mac os everything is fine, but on latest ubuntu the problem auto assigning port appear

testcontainers/testcontainers-dotnet#825 - same issue for .net

So what happening:

1. Starting a redis container (doesn't matter which one, it just an example)
2. withExposedPorts(6389) - let docker to auto assign host port
3. calling getMappedPort function -> may return ipv4 or ipv6 port, depends on your luck

Testcontainer Logs
...

Steps to Reproduce

1. In this environment ubuntu 22
2. With this config.
3. Run '...'

  const container = await new GenericContainer(
    `${options.imageName}:${options.imageTag}`,
  )
    .withExposedPorts(6379)
    .start();

  // eslint-disable-next-line no-console
  console.timeEnd(`start redis`);

  const redisConfig = {
    port: container.getMappedPort(6379),
    host: 'localhost',
  } satisfies RedisStartedConfig;

7. Run docker ps, and see that there are 2 ports actually

Environment Information

• Operating System: ubuntu
• Docker Version: 24+
• Node version: 20+
• Testcontainers version: 10.8.1

we temporary fixed it by retrieving ipv4 port from the docker inspect info:

import { StartedTestContainer } from 'testcontainers/build/test-container';

export function retrievePortFromBinding(
  container: StartedTestContainer,
  sourcePort: number,
): number {
  return Number.parseInt(
    // eslint-disable-next-line @typescript-eslint/no-explicit-any
    (container as never as any).inspectResult.NetworkSettings.Ports[
      `${sourcePort}/tcp`
    ].find((p: { HostIp: string; HostPort: string }) => p.HostIp === '0.0.0.0')
      .HostPort,
  );
}

[cristianrgreco]

Thanks for raising, I'll need to look into it. Testcontainers resolves a list of host IPs, the order of which is determined by several factors like node version and OS. When we get the mapped port we probably need to find the port where the host matches the order, similar as you've done

[vsamofal]

The order actually is quite random, even in one test execution, we do start redis & postgres, we have around 20 files with tests, and for each file we start dbs, and some files are passing and some not, seems like it's super random from docker side.

[cristianrgreco]

Yep I think docker returns the ports in random order, but we should be able to find the one we want by host