Registry Image Update Checker Action

Action to check if the base image was updated and your image (published on DockerHub or other registry) needs to be rebuilt. This action will use the registry'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	Required	Default value
base-image	String	Base Docker Image	true
image	String	Your image based on base-image	true
os	String	Operating system	false	GH action OS
arch	String	System architecture	false	GH action architecture
verbose	bool	Show verbose output	false	false

Note: os and arch are necessary if you are checking multiarch images and their OS and/or system architecture are different from the one used in the Github action.

If you use a simple image name, like nginx, it will be translated to the default Docker Hub library images as index.docker.io/library/nginx. If you use an image with an owner, like foo/bar, it will be translated to a Docker Hub images as index.docker.io/foo/bar.

The tag is optional, but you could supply it. It will default to latest. You can use it like index.docker.io/library/nginx:latest (full name) or nginx:latest.

Output

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

Examples

Simple update check

This is the only function of this action:

name: Check outdated images

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

jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout
        uses: actions/checkout@v2
      - name: Check if update available
        id: check
        uses: giggio/docker-image-update-checker@v2
        with:
          base-image: library/nginx:1.21.0
          image: user/app:latest
          os: linux # optional
          verbose: true # optional
      - name: Build and push
        uses: docker/build-push-action@v2
        with:
          context: .
          push: true
          tags: user/app:latest
        if: steps.check.outputs.needs-updating == 'true'

Build and update

This action both builds and also checks for an update. Notice the step.if condition:

name: Build image

on:
  schedule:
    - cron:  '0 4 * * *'
  workflow_dispatch:
  push:
    branches:
      - main
    tags:
      - "*"
    paths-ignore:
      - "**.md"
  pull_request:
    branches:
      - main
    paths-ignore:
      - "**.md"

jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout
        uses: actions/checkout@v2
      - name: Check if update available
        id: check
        uses: giggio/docker-image-update-checker@v2
        with:
          base-image: library/nginx:1.21.0
          image: user/app:latest
      - name: Build and push
        uses: docker/build-push-action@v2
        with:
          context: .
          push: true
          tags: user/app:latest
        if: success() && (contains(fromJson('["push", "pull_request"]'), github.event_name) || (steps.check.outputs.needs-updating == 'true' && github.event_name == 'schedule'))

Windows example

# rest of the file omitted
      - name: Check if update available
        id: check
        uses: giggio/docker-image-update-checker@v2
        with:
          base-image: mcr.microsoft.com/windows/servercore:ltsc2022
          image: user/app
          os: windows

See other examples and their runs in this repo.