DevOps: Docker, CI/CD & Deployment

Bridge the gap between coding and operations. Learn to containerize applications, automate workflows with GitHub Actions, and deploy to the cloud.

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1. Docker (Containerization)

Docker packages your application and its dependencies into a “container” that runs consistently on any environment (Dev, Stage, Prod).

Key Concepts

Image: The blueprint/template (read-only). Built from a Dockerfile.
Container: A running instance of an Image.
Dockerfile: A script containing instructions to build the image.

Hands-on: Dockerizing a Node.js App

Create Dockerfile in your project root:

# Base Image
FROM node:18-alpine

# Work Directory
WORKDIR /app

# Copy package.json and install dependencies
COPY package*.json ./
RUN npm install

# Copy source code
COPY . .

# Expose port
EXPOSE 3000

# Start command
CMD ["npm", "start"]

Build the Image:
```
docker build -t my-node-app .
```
Run the Container:
```
docker run -p 3000:3000 my-node-app
```

Docker Compose

Manages multi-container applications (e.g., App + Database). defined in docker-compose.yml.

version: '3'
services:
  web:
    build: .
    ports:
      - "3000:3000"
  redis:
    image: "redis:alpine"

2. CI/CD with GitHub Actions

Continuous Integration (CI): Automatically building and testing code changes. Continuous Deployment (CD): Automatically releasing code to production.

Setting up a Workflow

Create .github/workflows/main.yml:

name: CI/CD Pipeline

on:
  push:
    branches: [ "main" ]
  pull_request:
    branches: [ "main" ]

jobs:
  build-and-test:
    runs-on: ubuntu-latest

    steps:
    - uses: actions/checkout@v3

    - name: Set up Node.js
      uses: actions/setup-node@v3
      with:
        node-version: '18.x'

    - name: Install dependencies
      run: npm install

    - name: Run Tests
      run: npm test

  deploy:
    needs: build-and-test
    if: github.ref == 'refs/heads/main'
    runs-on: ubuntu-latest
    
    steps:
      - name: Deploy to Production
        run: echo "Simulating deployment to AWS/Heroku..."
        # Add actual deployment scripts here (e.g., AWS CLI, Heroku CLI)

What this does:

Triggers on push to main.
Spins up a Linux VM.
Installs Node & deps.
Runs tests.
If tests pass -> Deploys!

3. Deployment Strategies

1. Traditional VPS (Virtual Private Server)

Providers: DigitalOcean, Linode, AWS EC2.
Process: SSH into server, pull git repo, run npm start (usually with PM2 process manager).
Pros: Full control, cheap.
Cons: Manual maintenance (updates, security patches).

2. PaaS (Platform as a Service)

Providers: Heroku, Render, Railway, Fly.io.
Process: Push to Git -> Magic happens.
Pros: Zero config, auto-scaling, easy HTTPS.
Cons: More expensive at scale.

3. Serverless

Providers: AWS Lambda, Vercel Functions, Cloudflare Workers.
Process: Upload just the function code.
Pros: Pay-per-use, infinite scaling.
Cons: Cold starts, stateless limitations.

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