Specify the env file docker compose uses

Question

Is it possible to specify the env file that docker compose uses for variable substitution? Currently it defaults to ".env" but I have different flavours of compose files which should have different envs.

Answer 1

You can use inheritance for this. If you have one "base" service where you set up the environment, all of your other services can inherit from that.

Example:

version: "2"

services:
  base:
    env_file:
      - my_env.txt

  web:
    extends:
      service: base
    image: foo

  database:
    extends:
      service: base
    image: foo-db

The above example has everything in the same file, but you can also split this up into multiple files, where the base service would reside in a base.yaml file. You just need to add file: base.yaml to the extends section. Please see the documentation here.

I use this approach for setting the proxy variables for all containers. I have a proxy.yaml file that defines a proxy-app service that picks up the proxy environment variables from the shell. All of my real services extend the proxy-app service and thus inherit the environment settings from that service.