How to use Github actions to build a docker image

Setting Up a GitHub Repository with Docker and GitHub Actions

Setting Up a Git Repository

1. Create a new repository on GitHub.

2. Clone the repository to your local machine.

3. Ensure the following minimum required files are included in the repository:

   • .github/workflows/docker-build.yml: Defines the GitHub Actions workflow for building and pushing the Docker image.
   • Dockerfile: Contains the instructions to build the Docker image.
   • app.py: A simple Python script (e.g., print("Hello Test!")).
   • requirements.txt: Can be empty or contain dependencies.
   • .gitignore: Can be empty but is useful for ignoring unnecessary files.

Creating some files

• app.py

print("Hello Test!")

• requirements.txt

# This file can be left empty or include dependencies

• .gitignore

# This file can be left empty or include dependencies

• Dockerfile

# Use an official Python image as the base
FROM python:3.11

# Set the working directory in the container
WORKDIR /app

# Copy project files into the container
COPY . /app/

# Create a virtual environment in /app/venv
RUN python -m venv venv

# Activate the virtual environment and install dependencies
RUN /app/venv/bin/pip install --upgrade pip && \
    /app/venv/bin/pip install --no-cache-dir -r requirements.txt

# Run the application using the virtual environment
CMD ["/app/venv/bin/python", "app.py"]

• docker-build.yml

name: Build and Push Docker Image

on:
  push:
    branches:
      - main  # Change this if using a different branch

jobs:
  build:
    runs-on: ubuntu-latest

    steps:
      - name: Checkout Repository
        uses: actions/checkout@v3

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

      - name: Log in to DockerHub
        uses: docker/login-action@v2
        with:
          username: ${{ secrets.DOCKER_USERNAME }}
          password: ${{ secrets.DOCKER_PASSWORD }}

      - name: Build and Push Docker Image
        uses: docker/build-push-action@v4
        with:
          context: .
          file: ./Dockerfile
          push: true
          platforms: linux/amd64,linux/arm64
          tags: ${{ secrets.DOCKER_USERNAME }}/docker_test:latest

Note: I set up platforms as I will use the image on a Mac.

Storing Docker Hub Credentials in GitHub Secrets

Credentials must be stored securely in GitHub:

1. Go to GitHub > Your Repository > Settings > Secrets and variables > Actions.
2. Click New repository secret and add:
   • DOCKER_USERNAME = Your DockerHub username.
   • DOCKER_PASSWORD = Your DockerHub password.

A free DockerHub account allows only one private repository.

Verifying the Setup

After pushing changes to the repository, GitHub will automatically build and push the Docker image to DockerHub. You can verify the process:

• On DockerHub: Check that the image was successfully pushed.
• On GitHub: Inspect the logs in GitHub Actions to confirm the build and push process was completed successfully.