docker-compose：.env 文件未加载

Question

My docker-compose.yml

version: '3'
services:
  test:
    build: .

My Dockerfile

FROM alpine:latest
ENTRYPOINT echo $ARG1 $ARG2

My .env file

ARG1=argument100
ARG2=argument200

If I run docker-compose run test the empty line got printed. However, it I add env_file section to my docker-compose.yml I am getting the expected output.

New docker-compose.yml

version: '3'
services:
  test:
    build: .
    env_file:
    - .env

Running docker-compose again

$ docker-compose run test
argument100 argument200

Am I using an illegal way to pass arguments to the ENTRYPOINT command inside the Docker ? Why is .env not loaded automatically upon docker-compose run ?

Answer 1

The .env file is used to set variables in the docker-compose command itself that can be used to expand variables in the docker-compose.yml file itself. The env_file specification will define variables inside the containers. They operate at two different levels.

There's also a third type of variable, build args, that can be injected into the building of an image.

Each of these has a distinct purpose, and are not multiple ways to do the same thing.