Docker labels retriever

This action retrieves the values of labels from the metadata of an image on Docker Hub, GitHub Packages or Google Container Registry, by calling the Docker API. The image isn't actually pulled so it's very fast.

Usage

For each label of the image, this action sets an output whose name is the name of the label in lower case. You have to set an id for the step of this action, so you can use the outputs in the next steps of your workflow with ${{ steps.the_id.outputs.name_of_label }}.

Here's an example of a workflow where the values of two labels, version and maintainer, set when the image has been previously built, are retrieved:

    name: Example workflow
    on: push

    jobs:
      build:
        runs-on: ubuntu-latest
        steps:

          - name: Check labels
            id: labels # this id will be reused below
            uses: axel-op/docker-labels-retriever@v1.0.0
            with:
              image: owner/repo/image:tag
              registry: github-packages
              accessToken: ${{ secrets.GITHUB_TOKEN }}

          # You can then get the values
          - name: Another step
            # ... in an if condition:
            if: steps.labels.outputs.version == '...'
            # ... in an environment variable:
            env:
              VERSION: ${{ steps.labels.outputs.version }}
              MAINTAINER: ${{ steps.labels.outputs.maintainer }}
            # ... or directly in your scripts:
            run: |
              echo "${{ steps.labels.outputs.version }}"
              echo "${{ steps.labels.outputs.maintainer }}"

Inputs

registry: required. Accepted values are:
- docker-hub
- github-packages
- gcr (Google Container Registry)
image: required. Format is:
- namespace/repository with Docker Hub
- owner/repository/image_name with GitHub Packages
- project_id/image with Google Container Registry
You can add a specific tag. The tag latest will be used by default.

With Docker Hub

dockerHubUsername: required only for private images. It must be the username of an account that can access the image. Omit it with public images.
accessToken: required only for private images. It can be a password or an access token. Omit it with public images.

With GitHub Packages

accessToken: required, even with public images. In most cases the GITHUB_TOKEN should be fine.

With Google Container Registry

hostname: required. Hostname of the image. Could be:
- gcr.io
- eu.gcr.io
- us.gcr.io
- asia.gcr.io
accessToken: required only for private images. It must be a JSON key of a service account with sufficient privileges. Omit it with public images.