Docker Image Update Checker Action

This action checks if a Docker image needs to be updated based on the base image it uses (e.g. FROM nginx:1.21.0). By default it checks for all platforms, but you can specify the platforms to check.

Inputs

Name	Type	Description
base-image	String	Base Docker Image. This is the image you have as FROM in your Dockerfile
image	String	Your image based on base-image
platforms	String	Platforms to check (default all), e.g. linux/amd64,linux/arm64

Output

Name	Type	Description
needs-updating	String	'true' or 'false' if the image needs to be updated or not
diff-images	String	List of images (platforms) that need to be updated
diff-json	String	JSON output of the images (platforms) that need to be updated with the list of layers

Runners

The action works on ubuntu and windows runners with or without a docker/login-action step. Without a login step, it will perform an anonymous pull of the manifests, except for Docker Hub because the Runners already have a token provided by GitHub (I can't find any documentation on this, but the token is there and it works).

It also works on macos runners, but because docker is not installed on the runners, you can't use the docker/login-action, so you can only use it with public images and anonymous pulls.

Authentication

To authenticate with a Docker registry, you can use the docker/login-action in a step before this action.

Examples

• Minimal
• Single platform
• Multiple platforms

Minimal

Check if the image user/app:latest, that has nginx as a base image, needs to be updated:

name: Check docker image

on:
  schedule:
    - cron:  '0 4 * * *'

jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      - name: Check if update available
        id: check
        uses: lucacome/[email protected]
        with:
          base-image: nginx:1.21.0
          image: user/app:latest

      - name: Check result
        run: echo "Needs updating: ${{ steps.check.outputs.needs-updating }}"

Single platform

Check if the image user/app:latest, that has nginx has a base image, needs to be updated and build and push the image if needed:

name: Check docker image

on:
  schedule:
    - cron:  '0 4 * * *'

jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout
        uses: actions/[email protected]

      - name: Check if update available
        id: check
        uses: lucacome/[email protected]
        with:
          base-image: nginx:1.21.0
          image: user/app:latest
          platforms: linux/amd64

      - name: Build and push
        uses: docker/[email protected]
        with:
          context: .
          push: true
          tags: user/app:latest
        if: steps.check.outputs.needs-updating == 'true'

Multiple platforms

Check if the image user/app:latest, that has nginx has a base image, needs to be updated for linux/amd64 and linux/arm64:

name: Check docker image for multiple platforms

on:
  schedule:
    - cron:  '0 4 * * *'

jobs:
  check:
    runs-on: ubuntu-latest
    outputs:
      needs-updating: ${{ steps.check.outputs.needs-updating }}
    steps:
      - name: Login to Docker Registry
        uses: docker/[email protected]
        with:
          username: ${{ secrets.DOCKER_USERNAME }}
          password: ${{ secrets.DOCKER_PASSWORD }}

      - name: Check if update available
        id: check
        uses: lucacome/[email protected]
        with:
          base-image: nginx:1.21.0
          image: user/app:latest
          platforms: linux/amd64,linux/arm64 # Use 'all' to check all platforms

  build:
    needs: check
    runs-on: ubuntu-latest
    if: needs.check.outputs.needs-updating == 'true'
    steps:
      - name: Checkout
        uses: actions/[email protected]

      - name: Setup QEMU
        uses: docker/[email protected]
        with:
          platforms: arm64

      - name: Docker Buildx
        uses: docker/[email protected]

      - name: Build and push
        uses: docker/[email protected]
        with:
          context: .
          push: true
          tags: user/app:latest
          platforms: linux/amd64,linux/arm64

Note

The platforms input is optional and defaults to all.

Debugging

If something is not working as expected, you can enable debug logging to get more information (a lot more information). You can re-run the action with the Enable debug logging checkbox checked for a single run or set the ACTIONS_STEP_DEBUG secret to true in the repository's secrets. For more information on debugging actions, see Enabling debug logging.