Docker Compose how to extend service with build to use an image instead

Question

Having a base docker-compose.yml like the following:

version: '2'
services:
  web:
    build: .
...

How can I extend it to use an image instead?

docker-compose.prod.yml

version: '2'
services:
  web:
    image: username/repo:tag

Running it with docker docker-compose -f docker-compose.yml -f docker-compose.prod.yml up still promps:

Building web
Step 1/x : FROM ...

I tried with docker-compose -f docker-compose.yml -f docker-compose.prod.yml up --no-build:

ERROR: Service 'web' needs to be built, but --no-build was passed.

I'm expecting the "Pulling from name/repo message" instead. Which options do I have? Or do I need to create a complete duplicate file to handle this slight modification?

Answer 1

To use build instead image in docker-compose.override.yml you should replace image with local image name and then build this image with target.

In docker-compose.override.yml:

    image: username-repo-tag
    build:
      context: .
      target: username-repo-tag

In your Dockerfile you should add target to FROM tag:

FROM username/repo:tag as username-repo-tag
...
your instructions
...