Added the docker options override configuration for traefik

[stepbeekio]

See #98 for more detailed proposal. This change adds the additional_ports configuration for traefik. Includes documentation to give entrypoint examples for this escape hatch. The ruby code impacted is relatively small - we essentially just allow a user to add other published ports to the traefik container.

The obvious downside to this is that by using this configuration in isolation a user could bring down their service. Traefik wouldn't know which port to bind as the default entrypoint and would fail to serve traffic.

Added a unit test and tested locally against a running deploy.

[kjellberg]

This can also be used to enable port 443 for https. Just a thought, why not rename additional_ports to just ports, which defaults to [80]. People messing with ports should be smart enough to include port 80 if they configure it.

traefik:
  ports:
    - 80
    - 443
    - 9000

[stepbeekio]

@kjellberg That's a good point. I think it would fit better with moving away from traefik defaults too. I'll get time later today to edit.

[kjellberg]

Actually I need this right now. Was trying to enable https for a website but I had to patch mrsk to add port 443, just 5 seconds before you created this PR. Cloudflare messes up with session cookies, using flexible ssl, so would be nice to support additional ports.

If this get merged, I'd be happy to create a patch that enables ssl with as simple as:

servers:
  web:
    hostname: example.com
    hosts:
      - 206.189.112.50
traefik:
  ports:
    - 80
    - 443
  letsencrypt:
     email: [email protected]

Another thought:

What if two different projects deploys to the same server. How do we keep the traefik config consistent? Should mrsk support this?

Project A

traefik:
  ports:
    - 80
    - 9000
    - 9001

Project B

traefik:
  ports:
    - 80
    - 8080

Deploying Project B will override ports config from Project A. I guess we already have the same problem with args.

[stepbeekio]

@kjellberg Made suggested change to ports and updated README accordingly. Deployed a config using this locally and I like it.

[stepbeekio]

@dhh I've edited the optionize method to allow for nested lists inside arguments that get expanded. I figured that making optionize more flexible in what it accepted would be better than introducing a one-off for traefik options. I'm not a ruby dev so have no idea if there's a smarter way to do this.

[nerdinand]

I ran into problems with this feature with the ActiveSupport main-branch. There, docker_option_args returns [], because config.raw_config.dig(:traefik, "options") returns nil for some reason.