Docker has revolutionized the way we develop, ship, and run applications. In this comprehensive guide, we'll walk through containerizing a Node.js application from scratch to production-ready deployment.

Why Docker?

Docker solves the classic "it works on my machine" problem by packaging your application with all its dependencies into a standardized unit called a container. Benefits include:

  • Consistency - Same environment everywhere
  • Isolation - No conflicts between applications
  • Portability - Run anywhere Docker is installed
  • Scalability - Easy to replicate and scale

Basic Dockerfile

Let's start with a simple Dockerfile for a Node.js application:

# Use official Node.js image
FROM node:18-alpine

# Set working directory
WORKDIR /app

# Copy package files
COPY package*.json ./

# Install dependencies
RUN npm ci --only=production

# Copy application code
COPY . .

# Expose port
EXPOSE 3000

# Start application
CMD ["node", "server.js"]

Multi-stage Builds

For production, use multi-stage builds to reduce image size:

# Build stage
FROM node:18-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

# Production stage
FROM node:18-alpine
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
EXPOSE 3000
CMD ["node", "dist/server.js"]

Docker Compose

For applications with multiple services, use docker-compose.yml:

version: '3.8'

services:
  app:
    build: .
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=production
      - DATABASE_URL=postgres://db:5432/myapp
    depends_on:
      - db

  db:
    image: postgres:15-alpine
    volumes:
      - postgres_data:/var/lib/postgresql/data
    environment:
      - POSTGRES_DB=myapp
      - POSTGRES_PASSWORD=secret

volumes:
  postgres_data:

Useful Commands

  • docker-compose up -d - Start services in background
  • docker-compose logs -f - Follow logs
  • docker-compose down - Stop and remove containers
  • docker-compose build --no-cache - Rebuild images
Pro tip: Use .dockerignore to exclude unnecessary files like node_modules, .git, and .env from the build context.

Conclusion

Docker simplifies deployment and ensures consistency across environments. Start with simple Dockerfiles and gradually adopt more advanced patterns as your needs grow.

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