The BuildKit Cache Dance

Save RUN --mount=type=cache caches on GitHub Actions or other CI platforms

The BuildKit Cache Dance allows saving RUN --mount=type=cache caches on GitHub Actions or other CI platforms by extracting the cache from the previous build and injecting it into the current build.

Use cases:

• apt-get (/var/cache/apt, /var/lib/apt)
• Go (/root/.cache/go-build)
• etc.

This reproducible-containers/buildkit-cache-dance action was forked from overmindtech/buildkit-cache-dance (archived on September 2023). This action be used for "non-reproducible" containers too.

Examples

apt-get GitHub Actions

Dockerfile:

FROM ubuntu:22.04
ENV DEBIAN_FRONTEND=noninteractive
RUN \
  --mount=type=cache,target=/var/cache/apt,sharing=locked \
  --mount=type=cache,target=/var/lib/apt,sharing=locked \
  rm -f /etc/apt/apt.conf.d/docker-clean && \
  echo 'Binary::apt::APT::Keep-Downloaded-Packages "true";' >/etc/apt/apt.conf.d/keep-cache && \
  apt-get update && \
  apt-get install -y gcc

Action:

---
name: Build
on:
  push:

jobs:
  Build:
    runs-on: ubuntu-22.04
    steps:
      - uses: actions/checkout@v4
      - uses: docker/setup-buildx-action@v3
      - uses: docker/metadata-action@v5
        id: meta
        with:
          images: Build

      - name: Cache
        uses: actions/cache@v3
        id: cache
        with:
          path: |
            var-cache-apt
            var-lib-apt
          key: cache-${{ hashFiles('.github/workflows/test/Dockerfile') }}

      - name: inject cache into docker
        uses: reproducible-containers/[email protected]
        with:
          cache-map: |
            {
              "var-cache-apt": "/var/cache/apt",
              "var-lib-apt": "/var/lib/apt"
            }
          skip-extraction: ${{ steps.cache.outputs.cache-hit }}

      - name: Build and push
        uses: docker/build-push-action@v5
        with:
          context: .
          cache-from: type=gha
          cache-to: type=gha,mode=max
          file: Dockerfile
          push: ${{ github.event_name != 'pull_request' }}
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}

Real-world examples:

• https://github.com/rootless-containers/slirp4netns/blob/v1.2.2/.github/workflows/release.yaml#L18-L36
• https://github.com/containers/fuse-overlayfs/blob/40e0f3c/.github/workflows/release.yaml#L17-L36

CacheMap Options

Optionally, instead of a single string for the target, you can provide an object with additional options that should be passed to --mount=type=cache in the values cache-map JSON. The target path must be present in the object as a property.

      - name: inject cache into docker
        uses: reproducible-containers/[email protected]
        with:
          cache-map: |
            {
              "var-cache-apt": {
                "target": "/var/cache/apt",
                "id": "1"
              },
              "var-lib-apt": "/var/lib/apt"
            }
          skip-extraction: ${{ steps.cache.outputs.cache-hit }}

CLI Usage

In other CI systems, you can run the script directly via node:

curl -LJO https://github.com/reproducible-containers/buildkit-cache-dance/archive/refs/tags/v3.1.0.tar.gz
tar xvf buildkit-cache-dance-3.1.0.tar.gz

During injection:

node  ./buildkit-cache-dance-3.1.0/dist/index.js --cache-map '{"var-cache-apt": "/var/cache/apt", "var-lib-apt": "/var/lib/apt"}'

After build during extraction:

node  ./buildkit-cache-dance-3.1.0/dist/index.js --extract --cache-map '{"var-cache-apt": "/var/cache/apt", "var-lib-apt": "/var/lib/apt"}'

Here are the available options:

build-cache-dance [options]
Save 'RUN --mount=type=cache' caches on GitHub Actions or other CI platforms

Options:
  --extract      Extract the cache from the docker container (extract step). Otherwise, inject the cache (main step)
  --cache-map    The map of actions source to container destination paths for the cache paths
  --scratch-dir  Where the action is stores some temporary files for its processing. Default: 'scratch'
  --skip-extraction  Skip the extraction of the cache from the docker container
  --help         Show this help

Releases

v1

v1 follows the original design of overmindtech/buildkit-cache-dance.

v1 is composed of two actions:

• reproducible-containers/buildkit-cache-dance/[email protected]
• reproducible-containers/buildkit-cache-dance/[email protected]

See the releases/v1 branch.

v2

v2 is composed of the single reproducible-containers/buildkit-cache-dance action.

v3

Rewrote the action in TypeScript and adds support for cache-map that gets a string of files that need to be injected as a JSON string. This makes it possible to inject multiple directories in one call and simplifies the usage.

This release also makes it possible to run the script outside GitHub Actions in other CI platforms or locally using command line arguments.

Acknowledgement

• Thanks to Alexander Pravdin for the basic idea in this comment.
• Thanks to the authors of the original overmindtech/buildkit-cache-dance.