Docker Swarm with image versions externalized to .env file

The answer is quite simple: it's not a bug, nor a feature. .env is not currently supported by docker stack. You must source manually the .env running export $(cat .env) before running docker stack ...

There is an issue discussing this needs in the Docker Github. https://github.com/docker/docker.github.io/issues/3654 and another one discussing the problem and solution: https://github.com/moby/moby/issues/29133#issuecomment-285980447

The yaml parser in docker stack deploy doesn't have all the same features of that in docker-compose. However, you can use docker-compose config to output a yaml file after it's done all the variable substitutions, extending other files, and merging multiple files together. This effectively turns docker-compose into a preprocessor.

you can create a deploy.sh

export $(cat .env) > /dev/null 2>&1; docker stack deploy ${1:-STACK_NAME}

• The .env parses without regular expressions or unstable tricks.
• Errors on stderr produced by #comments inside the .env will be redirected to stdin (2>&1)
• Undesired prints of all export and error now on stdin too, are redirected to /dev/null. This prevents console flood.
• Those errors do not prevent .env being parsed correctly.

We can define STACK_NAME in our .env but we can also pass our customized stack_name

. deploy.sh <stack_name> (stack_name opcional)

This workaround gave me headaches for 3 nights