Environment variables in ARGS

Docker Engine Compose
1

I was playing around with args and env_file and realised the env_file does not work in args as it is stated in the docs: https://docs.docker.com/compose/compose-file/#envfile

Interestingly it DOES WORK if the env_file is called .env which is the default name. It seems this file is loaded earlier.

My docker-compose file looks as following:

# This should test the environment with the latest snapshots
# This is based on base.yml
version: '2'
services:
  elasticsearch:
    env_file:
      - snapshot.env
    build:
      context: Dockerfile
      args:
        TEST: ${TEST}

If I run docker-compose config I get the following output:

WARNING: The TEST variable is not set. Defaulting to a blank string.
networks: {}
services:
  elasticsearch:
    build:
      args:
        TEST: ''
      context: /Users/ruflin/Dev/tmp/compose-testing/Dockerfile
    environment:
      TEST: abcd
version: '2.0'
volumes: {}

If I now change the line - snapshot.env to -.env, rename also my env file and run it again, I get:

networks: {}
services:
  elasticsearch:
    build:
      args:
        TEST: abcd
      context: /Users/ruflin/Dev/tmp/compose-testing/Dockerfile
    environment:
      TEST: abcd
version: '2.0'
volumes: {}

This brings up two questions from my side:

  • Why does .env work and snapshot.env doesn’t?
  • Is there an option to specific env variables for args in a separate file?

The problem with .env auto discovery is that in case I have a second compose file which extends this one in a different directory, it will not interpret the .env file for the first composer file.

1 Like
2

Just on a related note, it appears that docker-compose run -e NAME=VALUE [...etc] has a similar problem – it doesn’t work as described in the docs, either. I get the same “variable is not set” message as your snapshot.env example gets. And I’m on docker-compose.yml v3.2.

Just adding to this thread on the off-chance that Docker notices …