Support inline default values for interpolation

[dnephin]

Implements part of #2441 to support inline default values.

I have no idea how robust this is, but it's a start.

[dnephin]

These 3 lines are the only real substantial modifications.

I also cut out the arg/kwarg handling and just replaced it with a mapping arg, since that's how we use it.

[aanand]

Nice. Maybe we should support ${VAR-default} as well, i.e. substitute the default if VAR is unset, but not if it's set to an empty string? That way you can override a variable to the empty string if you want to.

[dreyks]

oh, this is just what all of us need =) any hope this will be merged soon?

[marcellodesales]

@aanand, @dnephin What needs to be done to get this in? Have been waiting for this for a while

[nicooga]

What about using environment variables in key names? Like in:

version: '2'services:
postgres: {image: 'postgres:9.6'}redis: {image: 'redis:3.2.3'}web_server:
build: ../sources/myappdepends_on: [postgres]env_file: ../env/$ENV.envlinks: [postgres]volumes:
- myapp_${ENV}_source:/source
- myapp_nginx_socks:/tmp/sockssidekiq:
build: ../sources/myappcommand: bundle exec sidekiq -e $ENV -c 2 -q default -q carrierwavedepends_on: [postgres, redis]env_file: ../env/$ENV.envlinks: [postgres, redis]volumes_from: [web_server]volumes:
myapp_${ENV}_db: {external: true}myapp_${ENV}_source: {external: true}myapp_nginx_socks: {external: true}

For values it seems to be working right, but for keys it throws a syntax error:

ERROR: The Compose file './config/myapp.yml' is invalid because:
volumes value Additional properties are not allowed ('myapp_${ENV}db', 'myapp${ENV}_source' were unexpected)

BTW, is this on latest version? I'm getting variables interpolated with a fresh installed docker-compose.

$ docker-compose -v
docker-compose version 1.8.0, build f3628c7

[dnephin]

@marcellodesales I think we're going to try and get this into the next release for the v2.1 file format.

#3653 adds the v2.1 file format, so once that is merged I can rebase this and change it to only apply to the new format.

[dnephin]

What about using environment variables in key names?

Variables are not support in keys. Generally I think this is a bad idea, it leads to a lot of extra complexity.

In your case (and in just about every case so far where this has been requested), it is better to use the PROJECT_NAME or -p to vary the names instead of a variable in the key.

The discussion of variables in keys is not really relevant to this PR, so please open a new issue if you feel this is a necessary addition.

[marcellodesales]

@dnephin Sounds good... I can definitely be up to QA this... I reallllllly need it!

[shin-]

This needs to be rebased, but code LGTM

[aanand]

I'd still like to support ${VAR-default} syntax, if it's easy to implement.

[dnephin]

Ok, rebased, added the ${VAR-default} and gated the feature behind the Compose V2.1 version.

[shin-]

LGTM

[hadim]

Nice addition guys !

I am testing it at the moment the master git code and docker-engine 1.12 and it seems to work great except for volumes defaut values :

version: '2.1'
services:
test:
container_name: test-name
image: busybox
command: "true"
privileged: true
volumes:
- ${DATA_DIR-/home/hadim/test_data_dir}:/data:Z

I get the following error :

ERROR: Invalid interpolation format for "volumes" option in service "test": "${DATA_DIR-/home/hadim/test_data_dir}:/data:Z"

Am I missing something or is that a bug ?

Thanks

[shin-]

@hadim Looks like a bug - do you mind creating a separate issue for it? Thank you for your help!

[hadim]

Sure.

[glensc]

@dnephin#3108 (comment)

i proposed new syntax for 2.1 here:
#3998 (comment)

that shouldn't add complexity as keys can be still not interpolated and makes syntax more similar to other definitions.

[AlJohri]

@shin- With this config: ports: ["${PORT-8000}:${PORT-8000}"]

I'm getting this error: ERROR: Invalid interpolation format for "ports" option in service "app": "${PORT-8000}:${PORT-8000}"

Am I doing something wrong?

[shin-]

@AlJohri please share the output of docker-compose version and your entire Compose file.

[tmack8001]

I also get this same issue where defaults aren't supported... and my docker-compose version is the latest non release candidate, 1.22.0. I'm trying to add an environment variable and default into the "docker_host" of the image.

my-cool-container
image: ${DOCKER_HOST:-docker.something.internal.com}/namespace/my-cool-image:my-cool-tag

but I get the following error while executing docker-compose up:

ERROR: Invalid interpolation format for "image" option in service "my-cool-container": "${DOCKER_HOST:-docker.something.internal.com}/namespace/my-cool-image:my-cool-tag"

[shin-]

Additionally when using the 2.1 file format, it is possible to provide inline default values using typical shell syntax

https://docs.docker.com/compose/compose-file/compose-file-v2/#variable-substitution

Default values only with v2.1 or above.

[tmack8001]

ah thanks @shin- 👍 I was still referring to v2 🤕