Docker Image Update Checker Action

Action to check if the base image was updated and your image (published on DockerHub) needs to be rebuilt. This action will use Docker's API to compare the base layers of your image with the base-image, without the need to pull the images.

Inputs

Name	Type	Description
base-image	String	Base Docker Image
image	String	Your image based on base-image
platforms	String	Platforms to check

Output

Name	Type	Description
needs-updating	String	'true' or 'false' if the image needs to be updated or not

Examples

• Minimal
• Single platform
• Multiple platforms

Minimal

Check if the image user/app:latest, that has nginx has 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/docker-image-update-checker@v1
        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:

name: Check docker image

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

jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout
        uses: actions/checkout@v3

      - name: Check if update available
        id: check
        uses: lucacome/docker-image-update-checker@v1
        with:
          base-image: nginx:1.21.0
          image: user/app:latest

      - name: Build and push
        uses: docker/build-push-action@v3
        with:
          context: .
          push: true
          tags: user/app:latest
        if: steps.check.outputs.needs-updating == 'true'

Note

The platforms input is optional and defaults to linux/amd64.

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: Check if update available
        id: check
        uses: lucacome/docker-image-update-checker@v1
        with:
          base-image: nginx:1.21.0
          image: user/app:latest
          platforms: linux/amd64,linux/arm64

build:
    needs: check
    runs-on: ubuntu-latest
    if: needs.check.outputs.needs-updating == 'true'
    steps:
      - name: Checkout
        uses: actions/checkout@v3

      - name: Setup QEMU
        uses: docker/setup-qemu-action@v2
        with:
          platforms: arm64

      - name: Docker Buildx
        uses: docker/setup-buildx-action@v2

      - name: Build and push
        uses: docker/build-push-action@v3
        with:
          context: .
          push: true
          tags: user/app:latest
          platforms: linux/amd64,linux/arm64

Note

If any of the platforms is not present in either the base-image or the image, the action will exit with an error.

Debugging

To debug the action, you can set the DEBUG environment variable to true in the workflow file. The variable can be set at any level.

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/docker-image-update-checker@v1
        with:
          base-image: nginx:1.21.0
          image: user/app:latest
        env:
          DEBUG: true

To make it more convenient, you can use ${{ secrets.ACTIONS_STEP_DEBUG }} to enable debugging only when needed.

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/docker-image-update-checker@v1
        with:
          base-image: nginx:1.21.0
          image: user/app:latest
        env:
          DEBUG: ${{ secrets.ACTIONS_STEP_DEBUG }}

This works even when re-running the action with the Re-run job button and the Enable debug logging checkbox checked. To read more about debugging actions, see Debugging actions.