HTTP ports exposed in interact hook do not match the dockerfile EXPOSE

[cmacdonald]

Hence its difficult to document which ports a user should connect to.
See for example this from Terrier:

The jig could simply assume that it should expose the ports as they were requested.

[arjenpdevries]

I think (...) that the first time you run a docker exposing that port, it actually uses the port you request - but then the port is not available for the next time you run a docker exposing that port, so it automatically maps to a different one.

I.e., it is docker not the jig doing that, as far as I understand.

[ryan-clancy]

Yeah, by default Docker uses a random port on the host side so that containers that require the same port don't collide (i.e., we could both run a MySQL container on a server without colliding with each other).

We can add in some explicit port mappings within the jig (after the workshop, currently have no bandwidth) that are passed through to Docker.

[arjenpdevries]

After starting jig in interact mode, this command gives you the actual mapping:

docker port $(docker ps -aql)

If you expose 50000/tcp like us, you can request just the port number using:

 docker inspect --format='{{(index (index .NetworkSettings.Ports "50000/tcp") 0).HostPort}}' $(docker ps -aql)