I used to externalized my image versions to my .env file. This make it easy to maintain and I don't modify my docker-compose.yml file just to upgrade a version, so I'm sure I won't delete a line by mistake or whatever.
But when I try to deploy my services with stack to the swarm, docker engine complains that my image is not a correct reposity/tag, with the exact following message :
Error response from daemon: rpc error: code = 3 desc = ContainerSpec: "GROUP/IMAGE:" is not a valid repository/tag
To fix this, I can fix the image version directly in the docker-compose.yml file. Is there any logic here or it that a bug? But this mixes fix part of the docker-compose and variable ones.
Cheers, Olivier
As already mentioned the .env isn't currently supported by the docker stack.
So the alternative way is to clearly specify the environment file using by env_file, e.g.:
version: '3.3'
services:
foo-service:
image: foo-image
env_file:
- .env
environment:
- SOME_ENV=qwerty
- OTHER_ENV=${SOME_ENV} # Not supported
Update: as per 2024 it still does not support variable substitution neither in env_file nor in environment compose file entry.
Opposite to other answers here it would not either work for docker compose --file your.compose.yml config > processed.yml followed by docker stack deploy --compose-file processed.yml your-stack because the compose file formats for stack and compose mismatch (name, depends_on keys at least).