feat(core)!: add support for tc.host and de-prioritise docker:dind

[kiview]

What does this PR do?

Adds support for reading the tc.host property from the ~/.testcontainers.properties file. This config will have the highest priority for configuring the Docker client.

Why is it important

This brings Testcontainers Desktop support to testcontainers-python and aligns this language with the TestcontainersHostStrategy found it testcontainers-java.

Misc

I wasn't able to get a working testcontainers-python development environment set up on my M2 MacBook. This seems to be related to some kind of Cython 3.0.0 issue, that I don't fully understand and trying to fix it breaks the installation of further dependencies (like pymssql). So I was only able to test it in an Ubuntu Codespaces environment (also required some weird Cython workarounds).

Breaking Changes

• To prioritise tc.host this PR prioritised having that over true docker:dind use cases
• This means we stopped trying to automatically infer the container host IP when running inside a docker:dind container
• When using -v /var/run/docker.sock:/var/run/docker.sock you should be unaffected since your containers run on the original host

[kiview]

Had to do it, to get things working with Testcontainers Cloud within Codespaces (which runs inside a container). I also thought part of this code duplicate what is done in docker_client.py.

[totallyzen]

After some cleanup of the "read file" mechanism, it's LGTM.
Also updated the PR body to add details on why this is potentially a breaking change and what to do about it if you are affected.

[totallyzen]

private function -> moved to the bottom of this file

[massdosage]

We just got bitten by this change when we upgraded from version 3.5.0 to 4.8.1. We have a unit test which spins up a DockerContainer which has an application that exposes a REST end point over HTTP. We connect to this from the unit test to check it's available. So we used to do something like this:

        with DockerContainer(container).with_exposed_ports(8083) as container:
            url = f'http://{container.get_container_host_ip()}:{container.get_exposed_port(8083)}/'
            requests.get(url).raise_for_status()

When we run this in our CI pipeline it is using Docker within Docker and the URL generated above is http://172.17.0.1:32769/ for version 3.5.0. When we upgraded to 4.8.1 the URL changes to be of the form http://localhost:32769 which doesn't resolve and the test fails with a ConnectionRefusedError. I tried various forms of setting a value for tc.host such as tc.host=http://172.17.0.1:32769, tc.host=tcp://172.17.0.1:1234 and they all resulted in connection errors.

Eventually I resorted to moving the old behaviour that I found on this PR into my unit test like so

            if inside_container():
                host = container.get_docker_client().gateway_ip(container.get_wrapped_container().id)
            else:
                host = container.get_container_host_ip()
            url = f'http://{host}:{container.get_exposed_port(8083)}/'

and this works.

Am I doing something completely wrong or is this expected behaviour?

[kiview]

@massdosage Yeah, sorry for this breaking change. Back then the project was in a bit of a hanging state, with us taking over from the older maintainer, and in general, we were unsure how to go forward with this change.

I think for now, your workaround is very clever and thanks for sharing it, we intend to integrate a change like this acutally into the library directly again, to avoid the users having to code around it.

Would you be willing to look into contributing the fix to the library, since I think you understand the issue well and also have a good reproducer at hand? (cc @alexanderankin @balint-backmaker ).

[kiview]

Ah sorry @massdosage ,I see the community (@CarliJoy) is already working on it, maybe you can try to stay in the loop there:
#517 (comment)

[massdosage]

@kiview no problem, I know how these things go. I've joined the discussion on #517 and would be happy to review or try out any proposed changed.