Extend env_file behavior in the compose file to work like --env-file CLI option

[juergsch]

Description

Unfortunately, the two do have similar names but different behavior.

• This can be confusing.
• There seems to be no way to define a .env.override file inside the compose file for interpolation to e.g. override a path setting of the volumes section. Of course overriding could be done by the command line. But the composes file seems to be the right place for that.

Example:
The DATA_ROOT_DIR is defined in the .env file. For development, the .env.dev.override should define another location for DATA_ROOT_DIR.

--> In the example below, DATA_ROOT_DIR is taken from .env, not from .env.dev.override

services:
opensearch:
image: opensearchproject/opensearch:latest
container_name: opensearch
env_file:
- path: .env
- path: .env.dev.override
required: false
volumes:
- ${DATA_ROOT_DIR}:/usr/share/opensearch/data # Persist collected data
...

*** Thanks a lot for this great product ***

[ndeloof]

• This can be confusing.

Indeed, this is a source for many users to misunderstand interpolation not working as intended. But this is our legacy, we can't just change this. We could declare aliases to limit ambiguity, but issue will remain

• There seems to be no way to define a .env.override file inside the compose file for interpolation

Right, compose.yaml file is not expected to define the .env file path, otherwise there's no benefit to use variables !

I guess I'll have to close this feature request as "not planned".