Creating Docker Github action

This is an example how to create a simple Docker Github action. To get more familiar with Github actions, check official docs.

Start with an empty git repo:

mkdir docker-gha-example
cd docker-gha-example
git init

For repository to be considered a Github action, it is required to have a file action.yml or action.yaml, this metadata file will define inputs, outputs and run configuration.

name: Docker Github action
description: This is an example of Docker Github action
branding:
  icon: star
  color: yellow

inputs:
  name:
    description: who to greet
    required: false
    default: 'world'

outputs:
  greeting:
    description: greeting message

runs:
  using: docker
  image: Dockerfile
  args:
    - ${{ inputs.name }}

For more details on action.yml check docs.

Since docker image is referenced as Dockerfile, it is required to provide it inside repository.

FROM alpine:latest

RUN apk update && apk add bash && rm -rf /var/cache/apk/*

WORKDIR /workspace

COPY . /workspace

ENTRYPOINT [ "/workspace/entrypoint.sh" ]

In this example, an entrypoint is a bash script, so it is required to provide it in repository as well.

#!/bin/bash

echo "Hello $1"

Finally, to test the action, create a Github workflow in this repository under .github/workflows/main.yml.

name: Test action
on: push

jobs:
  test-action:
    runs-on: ubuntu-latest
    steps:
      - name: Run docker action
        id: docker-action
        uses: frennky/docker-gha-example@v1
        with:
          name: 'Github'

      - name: Print output
        run: echo ${{ steps.docker-action.outputs.greeting }}

Creating Docker Github action#

Creating Docker Github action