Add Support for hosts in the port bindings section

[frank-dspeed]

ports:

• host.box:10090:80

don't works because docker only accepts ips fig could dns request ports befor that and then supply the dns result to docker that would enable the users to deploy one fig.yml that will always bind to the right ip on the host.

[dnephin]

I think this is outside the scope of what compose should handle, however with environment variable interpolation (coming in 1.5.0), you'll be able to use a variable:

ports:
  - $HOST_IP:10090:80

That way you can do whatever you need to on the host to query for the correct ip, and have it injected into the docker-compose.yml using an environment variable.

HOST_IP=$(...) docker-compose up