docker-build-cache-config-action

This is an action to generate cache-from and cache-to inputs of docker/build-push-action for effective cache in pull request based development flow.

Problem to solve

Docker BuildKit supports cache.
It imports and exports cache by the following parameters:

cache-from: type=registry,ref=IMAGE
cache-to: type=registry,ref=IMAGE,mode=max

In pull request based development flow, cache is overwritten by pull requests and it causes cache miss.
For example,

1. Initially cache is set to main branch
2. When pull request B is opened,
   • Cache hit
   • Cache is overwritten to B
3. When pull request C is opened,
   • Cache miss
   • Cache is overwritten to C
4. When pull request B is merged into main,
   • Cache miss
   • Cache is overwritten to main branch

Solution

This action generates effective cache config for pull request based development flow.
Basically,

• Cache always points to base branch
• Don’t export cache on pull request

It would reduce time of docker build.

pull_request event

When a pull request is opened, this action instructs docker/build-push-action to import cache of the pull request branch with a fallback to the base branch and the default branch.
It does not export cache to prevent cache pollution.
For example,

cache-from: |
  type=registry,ref=IMAGE:head
  type=registry,ref=IMAGE:base
  type=registry,ref=IMAGE:main
cache-to:

push event of branch

When a branch is pushed, this action instructs docker/build-push-action to import and export cache of the branch with a fallback to the default branch.
For example,

cache-from: |
  type=registry,ref=IMAGE:head
  type=registry,ref=IMAGE:main
cache-to: |
  type=registry,ref=IMAGE:main,mode=max

push event of tag

When a tag is pushed, this action instructs docker/build-push-action to import cache of the default branch.
It does not export cache to prevent cache pollution.
For example,

cache-from: |
  type=registry,ref=IMAGE:main
cache-to:

Others

Otherwise, this action instructs docker/build-push-action to import cache of the triggered branch with a fallback to the default branch.
It does not export cache to prevent cache pollution.
For example,

cache-from: |
  type=registry,ref=IMAGE:head
  type=registry,ref=IMAGE:main
cache-to:

Example

Here is an example to use cache on GHCR (GitHub Container Registry).

      - uses: docker/metadata-action@v3
        id: metadata
        with:
          images: ghcr.io/${{ github.repository }}
      - uses: int128/docker-build-cache-config-action@v1
        id: cache
        with:
          image: ghcr.io/${{ github.repository }}/cache
      - uses: docker/build-push-action@v2
        id: build
        with:
          push: true
          tags: ${{ steps.metadata.outputs.tags }}
          labels: ${{ steps.metadata.outputs.labels }}
          cache-from: ${{ steps.cache.outputs.cache-from }}
          cache-to: ${{ steps.cache.outputs.cache-to }}

For monorepo

You can set a tag prefix to isolate caches.

      - uses: docker/metadata-action@v3
        id: metadata
        with:
          images: ghcr.io/${{ github.repository }}/microservice-name
      - uses: int128/docker-build-cache-config-action@v1
        id: cache
        with:
          image: ghcr.io/${{ github.repository }}/cache
          tag-prefix: |
            microservice-name--
      - uses: docker/build-push-action@v2
        id: build
        with:
          push: true
          tags: ${{ steps.metadata.outputs.tags }}
          labels: ${{ steps.metadata.outputs.labels }}
          cache-from: ${{ steps.cache.outputs.cache-from }}
          cache-to: ${{ steps.cache.outputs.cache-to }}

Inputs

Name	Default	Description
image	(required)	Image name to import/export cache
tag-prefix	[]	An array of tag prefixes

Outputs

Name	Description
cache-from	Parameter for docker/build-push-action
cache-to	Parameter for docker/build-push-action