Get or set env variable in docker-compose.yml file

Question

I have got a docker-compose.yml file and there I define:

extra_hosts:
- "localhost:${MY_MACHINE_IP}"

It works if I define MY_MACHINE_IP as environment var earlier.

What I want to achieve is to perform action like:

extra_hosts:
- "localhost:<get MY_MACHINE_IP from env if it exists, if not set MY_MACHINE_IP env variable with value <docker-machine-ip>>"

In other words: I want to define it in extra_hosts section, if MY_MACHINE_IP is already specified, get it, if not - set this env. variable with value = my docker machine ip.

Is it possible?

Answer 1

Yes in according to docker documentation

docker-compose run SERVICE env

So i think the variables are not global as you may think. You have to pass them as parameters. Read this .

Answer 2

You can use the package ruamel.dcw for that ( dcw for Docker Compose Wrapper, disclaimer: I am the author of that package). It allows you to create a section with key user-data in your docker-compose.yaml file, which is stripped out before handing the file to the normal docker-compose . That section can look like:

user-data:
  author: Your Name <your-name@youremail.com>
  description: container for postfix/submission
  env-defaults:
    PORT: 587    # override during development
    NAME: submission
    DOCKER_BASE: /data0/DATA

and then you can use {PORT} , {NAME} and {DOCKER_BASE} in the rest of the file, with the option of overriding these default values with environment variables.

The utility also write out a file .dcw_env_vars.inc which you can copy into your container and source to get the appropriate values into scripts you RUN from within the Dockerfile