Docker compose .env confusion

Background

I want to specify the location of .env file for variable substitution of docker-compose yml file, there is a need to separate .env, .production.env for different usage scenarios.

Problems

Some responses in stackoverflow quotes "env_file" keyword and --env-file tag which are not the same thing as .env file, env_file and --env-file tag only pass environment variables to containers, but not variable substitutions of docker-compose file, they are totally different things.

Solutions

cat the env file content to the docker compose file to read contents of .env with custom name. E.g.: alt.env

env $(cat alt.env) docker-compose up --build

References

- https://stackoverflow.com/a/67495905/2361494

Dot env file is not found in docker compose file

Background

So there is a case I need to substitue the variables defined in .env to the docker compose for further process, but when I run the docker-compose up command, the variable refer in docker compose file cannot be interpreted.  

Reason

Normally the .env file sits to the same directory as the docker compose yml file, and is expected the docker compose command being executed in the current directory of the docker compose file and the .env file, which I am not in this case.

Solutions

If the current directory is not the place where the compose file is sitting in, we need to specify --project-directory to allow docker-compose program to be able to recognize the directory where the yml file and the .env file sits in, the correct command after fixing is as follows

docker-compose -f {docker-compose-file-dir} --project-directory={directory-of-docker-compose-file} up -d