Support multi-stage build targets

[jahsome]

I may be going about this wrong, but I have a container which needs asset dependencies installed and compiled for a production build but not local/development builds. Specifically, I need to install npm dependencies and run gulp.

I couldn't think of a way to accomplish this, other than to create a multi-stage build in the Dockerfile and attempt to reference the specific stage but I don't see a way to do that with the init command.

If I have missed something or am attempting some grave sin by attempting this, I welcome any feedback.

Cheers!

[efekarakus]

😄 Heya @jake-harris !
Would modifying the build section of the manifest for your service help in this situation? https://github.com/aws/copilot-cli/wiki/Services#build
Under build there is an args property that map to the --build-args flag while building your container image. So I wonder if that can be used to refer to a specific stage.

If this helps, you can modify the manifest before deploying to the "test" environment and the image should build properly before pushing to the ECR repository.

[jahsome]

Thanks for the response!

Modifying the manifest with args would probably get me there, but would require some rethinking of my Dockerfile, and potentially eliminate the multi-stage build. Unfortunately I have other workflows dependent upon some of the stages so I don't think that's an option for me particularly.

Ideally, in the manifest, there would be a

image:
  build:
    dockerfile: path/to/dockerfile
    context: context/dir
    args:
      key: value
    target: my-build-stage

Which would output to:

docker build --file path/to/dockerfile --build-arg key=value context/dir --target=my-build-stage

[efekarakus]

Thanks yeah that totally makes sense, I've updated the issue with a feature request label for us to prioritize in our sprints!
As we make progress on the task, this issue will get updated.