GitHub Actions with Docker - Mini Project: Build & Apply

GitHub Actions with Docker

📖 Scenario: You work in a small team that wants to automate building a Docker image for your app whenever code is pushed to GitHub. You will create a GitHub Actions workflow file that builds a Docker image using a simple Dockerfile.

🎯 Goal: Build a GitHub Actions workflow file named docker-build.yml that triggers on pushes to the main branch, builds a Docker image from the provided Dockerfile, and tags it with latest.

📋 What You'll Learn

Create a basic Dockerfile with a simple command

Create a GitHub Actions workflow file named docker-build.yml

Configure the workflow to trigger on pushes to main

Add a job that builds the Docker image using the Dockerfile

Tag the Docker image as latest

💡 Why This Matters

🌍 Real World

Automating Docker image builds on code changes helps teams deliver software faster and with fewer errors.

💼 Career

Knowing how to use GitHub Actions with Docker is a key skill for DevOps engineers and developers working with containerized applications.

1

Create a simple Dockerfile

Create a file named Dockerfile with these exact contents:
FROM alpine:latest
CMD ["echo", "Hello from Docker"]

Docker

# Create a Dockerfile with FROM alpine:latest and CMD ["echo", "Hello from Docker"]

Need a hint?

Use FROM alpine:latest to start from a small Linux image.
Use CMD ["echo", "Hello from Docker"] to print a message when the container runs.

2

Create GitHub Actions workflow file

Create a file named .github/workflows/docker-build.yml and add the following header lines:
name: Docker Build
on:
push:
branches: [main]

Docker

FROM alpine:latest
CMD ["echo", "Hello from Docker"]

# Create .github/workflows/docker-build.yml with name and on push to main branch
# Your code here

Need a hint?

Use name: Docker Build to name the workflow.
Use on: push: branches: [main] to trigger on pushes to main branch.

3

Add job to build Docker image

In .github/workflows/docker-build.yml, add a job named build that runs on ubuntu-latest and uses these steps:
1. actions/checkout@v3
2. docker build -t myapp:latest . run in a run step

Docker

name: Docker Build
on:
  push:
    branches: [main]

# Add a job named build that runs on ubuntu-latest
# Add steps to checkout code and build Docker image tagged myapp:latest
# Your code here

Need a hint?

Use jobs: to define jobs.
Use runs-on: ubuntu-latest to specify the runner.
Use actions/checkout@v3 to get the code.
Use docker build -t myapp:latest . to build the image.

4

Print confirmation message

Add a final step in the build job that prints Docker image built successfully using a run step.

Docker

name: Docker Build
on:
  push:
    branches: [main]
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Build Docker image
        run: docker build -t myapp:latest .

# Add a step to print 'Docker image built successfully'
# Your code here

Need a hint?

Add a step with run: echo "Docker image built successfully" to show success.