Module 11: Docker in CI/CD

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Docker plays a vital role in modern CI/CD pipelines, enabling consistent builds, fast deployments, and portable workflows. In this module, we’ll see how Docker integrates with DevOps pipelines to build, test, and deploy applications automatically.

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🔹 1. Why Use Docker in DevOps Pipelines?

• ✅ Consistency – The same image works in dev, staging, and production.

• ✅ Portability – Works across any cloud or on-premise system.

• ✅ Speed – Build once, deploy anywhere.

• ✅ Scalability – Easily run in Kubernetes, ECS, or Swarm.

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🔹 2. Building and Pushing Images in CI/CD

The most common CI/CD step with Docker is building images and pushing them to a registry (Docker Hub, AWS ECR, GCP Artifact Registry, etc.).

👉 Example with GitHub Actions:

name: Build and Push Docker Image
on: [push]
jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout code
        uses: actions/checkout@v3

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

      - name: Build and push
        uses: docker/build-push-action@v4
        with:
          push: true
          tags: mydockerhubuser/myapp:latest

✅ Every commit automatically builds and pushes a fresh Docker image.

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🔹 3. Deploying Dockerized Apps Automatically

Once an image is built, CI/CD pipelines can deploy it automatically:

• To servers using SSH + docker run

• To Kubernetes clusters with kubectl

• To cloud services (AWS ECS, Google Cloud Run, Azure App Service)

This ensures code changes reach production faster.

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🔹 4. Example Pipeline with GitHub Actions

Here’s a simple pipeline for building and deploying a Node.js app using Docker:

name: CI/CD with Docker
on:
  push:
    branches: [ "main" ]

jobs:
  build-and-deploy:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3

      - name: Build Docker image
        run: docker build -t myapp .

      - name: Run tests
        run: docker run myapp npm test

      - name: Push image to Docker Hub
        run: |
          echo ${{ secrets.DOCKER_PASSWORD }} | docker login -u ${{ secrets.DOCKER_USERNAME }} --password-stdin
          docker tag myapp mydockerhubuser/myapp:latest
          docker push mydockerhubuser/myapp:latest

✅ Builds → tests → pushes → ready for deployment.

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🎯 Wrap Up

In this module, you learned how Docker fits into CI/CD pipelines by:

• Building and pushing images

• Automating deployments

• Running real-world pipelines with GitHub Actions

This makes Docker a cornerstone of modern DevOps workflows.

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