Docker.github.io: env_file list order / precedence in docker-compose.yml

[prometheas]

File: compose/compose-file/index.md, CC @londoncalling

Hey there! Please speak briefly to whether the env files towards the top or bottom of the list override env values that may be declared in multiple files. Thanks!

[londoncalling]

@shin- @dnephin can you address this question? I can add the details to the docs, but don't know the answer.

[dnephin]

I'm not sure I understand the question. env always overrides env_file

[prometheas]

@dnephin, given the following declaration in docker_compose.yml:

services:
  some-service:
    env_file:
      - a.env
      - b.env

And the following files:

# a.env
FOO=1

and

# b.env
FOO=hello

Will $FOO be 1 or hello?

[dnephin]

The order of the files is significant, yes. It will be hello

[alanjds]

Can we have this said explicitly on the docs please?

https://docs.docker.com/compose/compose-file/compose-file-v2/#env_file

[londoncalling]

@alanjds This was already added explicitly to the docs in the Version 3 Compose file per the referenced PR ^^ #3517, and is published at: https://docs.docker.com/compose/compose-file/#env_file

I've added further clarification in #3822, and will go ahead and update v2 and v1 with those same changes as well, in this case.

[alanjds]

@londoncalling I see. Thanks.

[londoncalling]

Updates are merged, so this should be published soon. Thanks, @alanjds .