Export layers to "regular" docker

Hi, thanks for the great action!

I’ve been trying to figure out how to export a buildx build to Docker that includes the layers. Right now I use load: true which allows me to run e.g. docker run subsequently, however now I’m trying to figure out how to export the layers as well.

I have a 2-step build. The first step is a build-push-action build that is cached between runs (using cache-to and saved with actions/cache). My second build is not cached, and re-uses the layers from the first build with cache-from. This second build is saved to docker (through load: true), so I can use docker run and other commands (build file below).

While I need build-push-action in the first build step (in order to export and cache the layers), I’d like to not use it in the second step, and use a regular docker build instead. The reason is that the second step wastes about a minute importing the output with cache-from. Unfortunately, I noticed that when I save the image with load: true, a subsequent docker build won’t be able to re-use the layers, but will see the image as a whole. Is there a way to export the layers from buildx so that I can use them in a regular docker build?

- uses: actions/checkout@v2

- name: Set up docker buildx
  uses: docker/setup-buildx-action@v1

- name: Cache docker layers
  uses: actions/cache@v2
  id: docker-cache
  with:
    path: /tmp/.buildx-cache
    key: ${{ runner.os }}-buildx-${{ hashFiles( '.dockerignore', 'Dockerfile', ...) }}

- name: Build base Docker image
  uses: docker/build-push-action@v2
  with:
    tags: my-image-cached
    cache-from: type=local,src=/tmp/.buildx-cache
    cache-to: ${{ (! steps.docker-cache.outputs.cache-hit) && 'type=local,dest=/tmp/.buildx-cache-new,mode=max' || '' }}
    target: cached # the cached bits are e.g. FROM ubuntu AS cached

# https://github.com/docker/build-push-action/issues/252
- name: Move cache
  run: |
    if [ -d /tmp/.buildx-cache-new ]
    then
      rm -rf /tmp/.buildx-cache
      mv /tmp/.buildx-cache-new /tmp/.buildx-cache
    fi

- name: Build final docker image
  uses: docker/build-push-action@v2
  with:
    tags: my-image
    load: true # effectively makes the image usable in 'docker run'
    cache-from: type=local,src=/tmp/.buildx-cache

- run: docker run my-image ...

[nmattia]

Thanks for all the help here, really appreciated! The workflow is much simpler and about twice as fast. Got yourself a new sponsor 😃

[crazy-max]

You’re welcome, see also https://github.com/dfinity/nns-dapp/pull/357#pullrequestreview-854258755 to export artifacts as it seems it’s what you want so it removes the load overhead.