env file-named volume in docker-compose - docker

Question

I'm new to Docker. I am writing a docker-compose file which creates 2 containers, foo and bar, sharing a volume data:
services:
foo:
container_name: foo
build: ./foo
volumes:
- data:/var/lib/
bar:
container_name: bar
build: ./bar
volumes:
- data:/var/lib/
depends_on:
- foo
volumes:
data:
Now, I want to use the environment variable TAG, to tag containers and volumes, in order to specify if it's for test or production. I expects something like this:
services:
foo:
container_name: foo_${TAG}
build: ./foo
volumes:
- data_${TAG}:/var/lib/
bar:
container_name: bar_${TAG}
build: ./bar
volumes:
- data_${TAG}:/var/lib/
depends_on:
- foo
volumes:
data_${TAG}:
Obviously, docker-compose is unhappy because of the last line containing data_${TAG}:.
How can I name my volume with TAG env variable?

Answer 1

If you create your volumes in advance, you can use the variable on external volume names like this (note that the reference inside of compose is a fixed name but it points to a variable external volume name):
$ cat docker-compose.volvar.yml
version: '2'
volumes:
data:
external:
name: test-data-${TAG}
services:
source:
image: busybox
command: /bin/sh -c 'echo From ${TAG} >>/data/common.log && sleep 10m'
environment:
- TAG
volumes:
- data:/data
target:
image: busybox
command: tail -f /data/common.log
depends_on:
- source
environment:
- TAG
volumes:
- data:/data
Create your volumes in advance with a docker volume create command:
$ docker volume create test-data-dev
test-data-dev
$ docker volume create test-data-uat
test-data-uat
$ docker volume create test-data-stage
test-data-stage
And here's an example of running it (I didn't use different directories or change the project name, so compose just replaced my containers each time, but I could have easily changed the project to run them all concurrently with the same results):
$ TAG=dev docker-compose -f docker-compose.volvar.yml up -d
Creating test_source_1
Creating test_target_1
$ docker logs test_target_1
From dev
$ TAG=uat docker-compose -f docker-compose.volvar.yml up -d
Recreating test_source_1
Recreating test_target_1
$ docker logs test_target_1
From uat
$ TAG=stage docker-compose -f docker-compose.volvar.yml up -d
Recreating test_source_1
Recreating test_target_1
$ docker logs test_target_1
From stage
$ # just to show that the volumes are saved and unique,
$ # rerunning uat generates a second line
$ TAG=uat docker-compose -f docker-compose.volvar.yml up -d
Recreating test_source_1
Recreating test_target_1
$ docker logs test_target_1
From uat
From uat

Answer 2

I don't know if this is possible like that but here is what I do:
I have a docker-compose.yml file like that
services:
foo:
container_name: foo_${TAG}
build: ./foo
volumes:
- /var/lib/
bar:
container_name: bar_${TAG}
build: ./bar
volumes:
- /var/lib/
depends_on:
- foo
And then I create a file docker-compose.override.yml that contains
services:
foo:
volumes:
- data_dev:/var/lib/
bar:
volumes:
- data_dev:/var/lib/
This way when you launch docker-compose, it will use the main file and use the other file to override its values.
You should then have 3 files:
docker-compose.yml
docker-compose.override-prod.yml
docker-compose.override-dev.yml
And then when you build you have the choice between those 2:
(What I do) I copy docker-compose.override-.yml to docker-compose.override.yml and Docker Compose with automatically takes those 2 files
You can provide the 2 files to use to the docker compose file (I forgot what the paramter is... I guess it's "-f")
I hope it helps