Image and build together

[dnephin]

Fixes #2092

Allow both image and build in a service config, and use image as the image name when building, if it exists.

[dnephin]

Rebased, now only applies to V2 config.

[aanand]

LGTM

[graingert]

@dnephin does this allow something like:

# docker-compose.yml
production:
   - image: ham/spam
   - build: ./spam
development:
   - image: ham/spam-dev
   - build: ./spam
   - dockerfile: Dockerfile-dev

# spam/Dockerfile
FROM ubuntu
RUN apt-get install nginx npm
COPY . /usr/bin/src/
RUN npm build
EXPOSE 80 443
CMD ["nginx", "-g", "daemon off;"]

# spam/Dockerfile-dev
FROM ham/spam # build on parent ham/spam.
RUN npm start # start live reloader

[aanand]

@graingert Yes, but you have to use the v2 file format to use image and build together:

version: 2
services:
  production:
    image: ham/spam
    build: ./spam
  development:
    image: ham/spam-dev
    build:
      context: ./spam
      dockerfile: Dockerfile-dev

You probably wouldn't actually define development and production as separate services in the same file, though. More likely you'd put the core config in docker-compose.yml and the development override in docker-compose.override.yml:

# docker-compose.yml
version: 2
services:
  spam:
     image: ham/spam
     build: ./spam

# docker-compose.override.yml
version: 2
services:
  spam:
    image: ham/spam-dev
    build:
      context: ./spam
      dockerfile: Dockerfile-dev

[graingert]

@aanand How does docker-compose know it needs to build "ham/spam" for docker-compose.override.yml's Dockerfile-dev to work?

[aanand]

I see what you were getting at now. Compose doesn't support dependent builds - you should use a tool like Shipwright for that.

[graingert]

@aanand ah nice, thanks

[dnephin]

I've been prototyping a tool in https://github.com/dnephin/dobi that would support building chains of images (as well as a bunch of other things). There are a few docs and examples, but it could definitely use more, I need one for the ordered build use case.