Expose port 3306 of MySQL container

[ocean90]

To allow accessing the container from external the port 3306 should get exposed. This is done by defining ports in the config, see ​https://docs.docker.com/compose/compose-file/#ports.

To retrieve the host port you can then use docker-compose port mysql 3306.

[peterwilsoncc]

48281.2.diff​ accounts for users that may be exposing a database on the default port:

• sets default to a non-standard value, 8836
• allows users to change the port using an environment variable, similar to the local port for the web server

[ocean90]

Replying to peterwilsoncc:

48281.2.diff​ accounts for users that may be exposing a database on the default port:

That’s why my patch only defines the container port to allow docker-compose to choose an ephemeral host port.

[donmhico]

+1 to this. I've tested 48281.2.diff and it works. Hopefully this gets committed soon.

[SergeyBiryukov]

In 47225:

Build/Test Tools: Expose port 3306 of MySQL container.

This only defines the container port to allow docker-compose to choose an ephemeral host port.

Props ocean90, peterwilsoncc.
Fixes #48281.