Support changing the listening port via $POSTGRES_PORT

[cansjt]

I am aware of issues #302 and #196. I do believe, though, the issue still hasn't been properly addressed.

Indeed in those issues, the solutions provided all assumes you are in control of the command line that starts the container (with docker) or use docker-compose. But there are plenty of use cases where these assumptions do not hold. Especially in a cloud context. PaaS and CI/CD systems, to name a few, do not necessarily let you provide extra arguments to the container's startup command line. Leaving us with environment variables as the only mean to configure the container (if you don't want to build a docker image of your own).

It would be extremely helpful if that feature was implemented here, instead of having to implement it on your own when needed.

So, please, do reconsider implementing this (#196 contains a solution, though I have not tested it). Thanks.

[tianon]

All the CI/CD systems I'm aware of that didn't previously allow customizing the container command have since added support for doing so (since customizing the container command is every bit as important for customizing a container as environment variables are). Do you have any more specific examples of systems which still do not support modifying command?

[cansjt]

@tianon Sorry for the lag. We use CircleCI. Their CI system is container based, you can do some level or Docker in Docker, but mostly to build docker images, not to run docker containers as services. They do offer VMs, within which you can run plain docker commands. But their VM images are clearly not their priority and quite outdated. Which leads you to lengthy updates within the CI build itself, which is a waste of time, on top of the VM start-up time which is not great.

[yosifkit]

command is in the docker section of the documentation that you link to:

jobs:
  build:
    docker:
      - image: buildpack-deps:trusty # primary container
        environment:
          ENV: CI

      - image: mongo:2.6.8
        command: [--smallfiles]

      - image: postgres:9.4.1
        environment:
          POSTGRES_USER: root

      - image: redis@sha256:54057dd7e125ca41afe526a877e8bd35ec2cdd33b9217e022ed37bdcf7d09673

So you should be able to add command to postgres just like they do to mongo.