How to customize network name in docker-compose file - docker-compose

Question

version: '3.8'
services:
foo:
...
networks:
- $FOO_NETWORK
networks:
foo_network:
I am unable to use $FOO_NETWORK under networks, i.e. it allows only to enter a value and not an ENV variable. How do I customize the network name to be taken from the environment variable instead

Answer 1

Environment variables are for values, you want to use it for a key. As far as i know this isn't supported yet and I'm not sure if it'll ever be.
One way you can customise this is to use multiple docker-compose files. Create three files:
one.yml:
version: "3.0"
services:
test:
image: nginx
two.yml:
version: "3.0"
services:
test:
networks:
foo: {}
networks:
foo: {}
three.yml:
version: "3.0"
services:
test:
networks:
bar: {}
networks:
bar: {}
Now you if you run it like this:
docker-compose -f one.yml -f two.yml up
or like this:
docker-compose -f one.yml -f three.yml up
You'll see that the files are merged:
Creating network "network_foo" with the default driver
Recreating network_test_1 ... done
...
Creating network "network_bar" with the default driver
Recreating network_test_1 ... done
You can even spin all three at once:
docker-compose -f one.yml -f two.yml -f three.yml up
Creating network "network_foo" with the default driver
Creating network "network_bar" with the default driver
Creating network_test_1 ... done
Attaching to network_test_1
test_1 | /docker-entrypoint.sh: /docker-entrypoint.d/ is not empty, will attempt to perform configuration
Check out documentation for more: https://docs.docker.com/compose/extends/
Also there is another way, which actually involves using variables to select a network. The way is to use existing networks. You'll need an .env file for this:
network=my_network
and in compose file you do like this:
version: "3.8"
services:
test:
networks:
mynet: {}
networks:
mynet:
external: true
name: $network
As you see there is an option to provide name when using an external network. The network with the name must exist when you start your containers or you'll get an error. You can use a separate file to create networks on a node or just create using CLI. Note that the compose version changed, the feature isn't supported in "3.0".