Docker & containerization

Perfect — let’s go through Docker & containerization for Node.js, which is essential for consistent, portable, and scalable deployments.

1️⃣ What is Docker?

Docker = platform for containerizing applications
Container = lightweight, isolated environment with all dependencies included
Benefits:
- Consistent environments across development, staging, production
- Portable → runs anywhere Docker is installed
- Scalable → works well with orchestration tools (Kubernetes, Docker Swarm)

2️⃣ Why Use Docker with Node.js?

Avoid “it works on my machine” problems
Package Node.js runtime + npm modules + environment variables together
Easy deployment to cloud providers (AWS, DigitalOcean, Heroku, Vercel)
Works well with CI/CD pipelines

3️⃣ Docker Basics

a) Dockerfile

Defines how to build your container image

# Use official Node.js LTS image
FROM node:20
 
# Set working directory
WORKDIR /app
 
# Copy package.json and install dependencies
COPY package*.json ./
RUN npm install
 
# Copy application code
COPY . .
 
# Expose port
EXPOSE 3000
 
# Start the app
CMD ["node", "index.js"]

FROM → base image
WORKDIR → sets working directory inside container
COPY → copies files into container
RUN npm install → installs dependencies inside container
CMD → command to run the app

b) Build Docker Image

docker build -t my-node-app .

c) Run Container

docker run -p 3000:3000 my-node-app

Maps container port 3000 to host port 3000

4️⃣ Docker Compose

Define multi-container apps (Node.js + database) in docker-compose.yml

version: "3"
services:
  app:
    build: .
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=production
    depends_on:
      - db
 
  db:
    image: postgres:16
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: postgres
      POSTGRES_DB: mydb
    ports:
      - "5432:5432"

Start all services: docker-compose up
Stop all services: docker-compose down

5️⃣ Benefits for Node.js Applications

Environment consistency → works the same on dev, staging, production
Dependency isolation → no conflicts with system Node.js version
Portability → deploy anywhere Docker is supported
Scalability → works with container orchestration platforms

6️⃣ Best Practices

Use small base images (e.g., node:alpine) for smaller containers
.dockerignore → exclude unnecessary files (node_modules, logs)
Multi-stage builds → reduce final image size
Set NODE_ENV=production in production containers
Use Docker Compose for development with multiple services

7️⃣ Key Takeaways

Docker makes Node.js apps portable, consistent, and scalable
Combine with PM2, environment variables, and CI/CD pipelines for production-ready deployments
Works well with databases, caching, and other microservices in containers

Next, we could cover Node.js production best practices, combining performance, monitoring, logging, security, clustering, and deployment strategies for real-world apps.

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