How to use custom host-to-IP mapping

[BenjaminQuandt]

Hi,

i want to use the custom host-to-IP mapping feature from docker. As docker handle the /etc/hosts file a bit special, there is a option to add those entries with the "--add-host" Flag.

see in reference:
https://docs.docker.com/engine/reference/commandline/run/

I didn't see any option to do that in testcontainers for now. Can someone explain how u should use it here?

[mchenla]

Use GenericContainer.withExtraHost(hostname, ipAddress). Add it to your existing container configuration before calling start():

container.withExtraHost("service.internal", "192.0.2.10");

This is the Testcontainers equivalent of:

docker run --add-host service.internal:192.0.2.10 ...

It adds the hostname/IP mapping to the container's /etc/hosts; it does not modify the host machine's hosts file. The IP above is just an example—replace it with an address reachable from your container. The mapping itself does not expose ports or establish connectivity.

This API was already present in Testcontainers 1.18.3: GenericContainer source. Its implementation passes these mappings to Docker's extra-hosts configuration.

AI-assisted answer, checked against the linked source; the example was not run locally.