Compose: Support a custom network name for default network

[arun-gupta]

Docker Compose has only --x-networking and --x-network-driver options. --x-networking creates a new bridge or overlay network depending upon where the application is targeted to.

It would be useful to have an option, similar to --net that would allow to target the entire Compose file to a pre-created network. Otherwise existing Compose files will have to be changed.

[dnephin]

You can set the project name with -p or COMPOSE_PROJECT_NAME, which is used as the network name as well.

I think we'd like to supposed a way to set the network name to a different default, but I'm not sure what that will look like yet. Some discussion in #745

[arun-gupta]

Here is the flow I was thinking:

• Create a new overlay network using docker network create
• Use that network with Compose file as docker-compose -n <NETWORK> up -d.

docker-compose -p <PROJECT> up -d will create the network based upon project name. Specifying -n will give an option to override network name.

[aanand]

Have started a tangentially related discussion of specifying networks to join in https://github.com/docker/compose/issues/2478.

[schmunk42]

As far as I remember from my tests you can also create a network and use:

docker network create mynet

app:
   net: 'mynet'

But you need it for every service.

[arun-gupta]

@schmunk42 yes, aware of that but generally all services would be running in the same overlay network. For example, testing can be be done in a bridge network, then in overlay network using Machines, and finally in overlay network on Cloud. So retargeting to different networks would be useful as opposed to baking it in the Compose file.

@aanand will contribute to #2478.

[kevstigneev]

@arun-gupta Compose 1.5 supports variable substitution. E.g.

app:
    net: ${CUSTOM_NET}

CUSTOM_NET=<NETWORK> docker-compose -p <PROJECT> should do the trick.

[dnephin]

I've updated the title to reflect the difference between this issue and #2478

[arun-gupta]

@kevstigneev that worked, scheduled a blog on that.

[aboltart]

One interesting thing what I mentioned. When is used network name with underscore

docker network create test_net

docker network inspect test_net
[
    {
        "Name": "test_net",
        "Id": "92529edbf2f104e174d97c3b4da5e39ca0faca5043004b694fb7a3de728d25db",
        "Scope": "local",
        "Driver": "bridge",
        "IPAM": {
            "Driver": "default",
            "Config": [
                {}
            ]
        },
        "Containers": {},
        "Options": {}
    }
]

docker-compose create network ignoring underscore

docker-compose -f projects/docker/compose/development/definitions/convert.yml --x-networking -p test_net run --rm convert_console bin/rails console
Creating network "testnet" with driver "None"

If used COMPOSE_PROJECT_NAME variable behaviour is the same

-bash-4.2$ docker network ls
NETWORK ID          NAME                DRIVER
92529edbf2f1        test_net            bridge
d9b56ef52ec4        testnet             bridge

[dnephin]

This is a side-effect of using the project name. We normalize the project name, but #2119 is an open issue to consider dropping the normalization.

Either way, allowing a way to set the network name separately fixes it for networks.

[aanand]

Given how we've now implemented networking and network configuration, I think the original stated use case ("target the entire Compose file to a pre-created network") can be served by doing this:

networks:
  default:
    external:
      name: pre-created-network

@arun-gupta: if you're happy with that, I'm going to close this issue.

[arun-gupta]

LGTM

[asfaltboy]

Perhaps it's worth adding the default network name override to the documentation (the syntax to specify external: true also changed)?

I see a PR for this was created already in #9660 , could we review and merge it to save everyone time in the future?