Implement 'overwrite_mutlivals' config option

[shcallaway]

In your docker-compose.override.yml, the overwrite_multivals config option allows you to specify which multivalue fields should be overwritten instead of concatenated with the base.

For example:

services:
  gateway:
    ports:
      - "80"
    overwrite_multivals:
      - ports

I am totally ripping off this guy's idea: #3939

This PR is a work in progress. Todo:

• compose/config/validation.py
• Unit tests
• Documentation

[shcallaway]

Do users want a generalized overwrite_multivals option? Or do they only care about overwriting ports? I have opened a separate PR for the latter: #5355

[leonaves]

+1

[drsharp]

@shcallaway I would vote for a generalized option...

we have a use case where the depends_on section is different for some of us in development. For example, the base docker compose for a given service we have depends on two cache stores, one for worker jobs and one for key-value storage. In development, we just run a single Redis for both, but we need them separate in non-development environments. It would be nice to be able to override the depends_on section and rewrite it, but currently the overrides just append.

So consider this a vote in favor of something more general than just ports.

note, if I could "fish my wish" it would simply be that whatever key I put in an override would fully override that key, not append. That would mean if I have something like:

services:
  xyz:
    ports:
       - "443:9876"
    depends_on:
      - service-a
      - service-b
      - service-c

and I wanted it to also depend on service-d in my local development, then I'd have my override look like:

services:
  xyz:
    depends_on:
      - service-a
      - service-b
      - service-c
      - service-d

Currently, to just add an extra service, I can just add that one (because it appends) but I would much prefer the flexibility of a per-section overwrite. For example, in the case I mentioned at the start, if the base uses service-a, service-b, and service-c, but I only want to depend on service-a and service-b, then a full per-key overwrite would allow me to set:

services:
  xyz:
    depends_on:
      - service-a
      - service-b

and be good to go.

I know this may be a corner case, but the idea of only appending when it's a list just seems overly constrictive to me.

[d0ruk]

Currently the only (besides the COMPOSE_FILE) solution is;

docker-compose -f docker-compose.yml -f docker-compose.prod.yml up

The only difference between the dev and prod configs is some ports arrays. I can just do

docker-compose -f docker-compose.yml up for prod, if this feature merged into upstream.

Anyone?

[nyetwurk]

Please take this

[robtayl0r]

+1

[shcallaway]

Closing because this particular design won't be approved. I may revisit this feature in the future.