Build and Publishing Docker Image via GitHub Workflow

What is GitHub Actions and GitHub Workflows?

GitHub Actions

GitHub Actions is a continuous integration and continuous delivery (CI/CD) platform that allows you to automate your build, test, and deployment pipeline. You can create workflows that build and test every pull request to your repository, or deploy merged pull requests to production.

GitHub Actions goes beyond just DevOps and lets you run workflows when other events happen in your repository. For example, you can run a workflow to automatically add the appropriate labels whenever someone creates a new issue in your repository.

GitHub provides Linux, Windows, and macOS virtual machines to run your workflows, or you can host your own self-hosted runners in your own data center or cloud infrastructure.

GitHub Workflows

A workflow is a configurable automated process that will run one or more jobs. Workflows are defined by a YAML file checked in to your repository and will run when triggered by an event in your repository, or they can be triggered manually, or at a defined schedule.

Workflows are defined in the .github/workflows directory in a repository, and a repository can have multiple workflows, each of which can perform a different set of tasks. For example, you can have one workflow to build and test pull requests, another workflow to deploy your application every time a release is created, and still another workflow that adds a label every time someone opens a new issue.

Let’s Start

1. Create Dockerfile

To create Dockerfile and add it to GitHub repository

1. Create a DockerFile with ARG variable.
2. Create two branchs - latest.

Example:

ARG BUSYBOX_TAG
FROM busybox:${BUSYBOX_TAG}

2. Create Workflow

To create workflow file

1. Create .github/workflow folder inside the GitHub repository.
2. Create docker-image.yml workflow file.
3. Copy and paste following code into docker-image.yml file.

Example:

name: Docker Image CI

on:
  push:
    branches: [ "latest" ]

jobs:

  build:

    runs-on: ubuntu-latest
    
    steps:
    
    # Checkout a Git repository at a particular version
    - name: Checkput
      uses: actions/checkout@v3

    # Set up Docker Buildx
    - name: Docker Setup Buildx
      uses: docker/setup-buildx-action@v3.0.0
    
    # Login against a Docker registry
    - name: Docker Login
      if: github.event_name != 'pull_request'
      uses: docker/login-action@v3.0.0
      with:
        username: ${{ secrets.HUB_USERNAME }}
        password: ${{ secrets.HUB_ACCESS_TOKEN }}

    # Extract metadata (tags, labels) for Docker
    - name: Docker Metadata action
      uses: docker/metadata-action@v5.0.0
      with:
        images: ${{ vars.IMAGE_NAME }}
    
    # Build and push Docker images
    - name: Build and push Docker images
      uses: docker/build-push-action@v5.0.0
      with:
        build-args: BUSYBOX_TAG=${{ vars.BUSYBOX_TAG }}
        context: .
        file: ./Dockerfile
        labels: ${{ steps.meta.outputs.labels }}
        platforms: linux/amd64,linux/arm64,linux/arm/v6,linux/arm/v7
        push: ${{ github.event_name != 'pull_request' }}
        tags: ${{ vars.IMAGE_NAME }}:${{ vars.BUSYBOX_TAG }}

    # Update a Docker Hub repository description from README.md
    - name: Docker Hub Description
      uses: peter-evans/dockerhub-description@v3.4.2
      with:
        username: ${{ secrets.HUB_USERNAME }}
        password: ${{ secrets.HUB_ACCESS_TOKEN }}
        repository: ${{ vars.IMAGE_NAME }}
        short-description: Docker Image - My BusyBox
        readme-filepath: ./README.md

3. Create Secrets and Variables

Secrets in GitHub workflow file

Name	Description
secrets.HUB_USERNAME	Username used to log against the Docker registry
secrets.HUB_ACCESS_TOKEN	Password or personal access token used to log against the Docker registry

Variables in GitHub workflow file

Name	Description
vars.IMAGE_NAME	Base name of Docker images
vars.BUSYBOX_TAG	Tag of Docker images

Create Repository Secrets and Variables

1. Navigate to the main apge of repository.
2. Under your repository name, click Settings. If you cannot see the Settings tab, select the dropdown menu, then click Settings.
3. In the Security section of the sidebar, select Secrets and variables, then click Actions.

Create Secrets

1. Click the Secrets tab.
2. Click New repository secret.
3. In the Name field, type a name for your secret.
4. In the Secret field, enter the value for your secret.
5. Click Add secret.

Create Variables

1. Click the Variables tab.
2. Click New repository variable.
3. In the Name field, type a name for your variable.
4. In the Value field, enter the value for your variable.
5. Click Add variable.

Create Environment Secrets and Variables

1. Navigate to the main page of the repository.
2. Under your repository name, click Settings. If you cannot see the Settings tab, select the dropdown menu, then click Settings.
3. In the left sidebar, click Environments.
4. Click on the environment that you want to add a secret to.

Create Secrets

1. Under Environment secrets, click Add secret.
2. Type a name for your secret in the Name input box.
3. Enter the value for your secret.
4. Click Add secret.

Create Variables

1. Under Environment variables, click Add variable.
2. Type a name for your secret in the Name input box.
3. Enter the value for your secret.
4. Click Add variable.

4. Test Workflow

1. Since workflow’s trigger is a push event on latest branch.
2. Push a commit on latest branch.
3. Under your repository name, click Actions. If you cannot see the Actions tab, select the dropdown menu, then click Actions.
4. The commit message for the push that triggered the workflow will be visible.
5. Once the workflow completed, click the commit message to check the status of workflow.

5. Check Docker Image on DockerHub

Now, the Docker image already push to your registry.

References

• GitHub Actions Documentation

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