Docker for Developers

Learn Docker fundamentals, container orchestration, and best practices for development workflows.

Docker Basics

What is Docker?

Docker packages your application and its dependencies into a standardized unit called a container. Containers are lightweight, portable, and consistent across environments.

Key Concepts

• Image: A read-only template for creating containers
• Container: A running instance of an image
• Dockerfile: Instructions for building an image
• Volume: Persistent storage for containers
• Network: Communication between containers

Dockerizing a Node.js App

# Build stage
FROM node:20-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

# Production stage
FROM node:20-alpine AS runner
WORKDIR /app
ENV NODE_ENV=production
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
COPY package*.json ./
EXPOSE 3000
CMD ["node", "dist/index.js"]

Docker Compose

Orchestrate multi-container applications:

version: '3.8'
services:
  app:
    build: .
    ports:
      - "3000:3000"
    environment:
      - DATABASE_URL=postgres://user:pass@db:5432/myapp
    depends_on:
      - db
      - redis

  db:
    image: postgres:16-alpine
    environment:
      POSTGRES_DB: myapp
      POSTGRES_USER: user
      POSTGRES_PASSWORD: pass
    volumes:
      - pgdata:/var/lib/postgresql/data

  redis:
    image: redis:7-alpine
    ports:
      - "6379:6379"

volumes:
  pgdata:

Development Workflow

# docker-compose.dev.yml
services:
  app:
    build:
      context: .
      dockerfile: Dockerfile.dev
    volumes:
      - .:/app
      - /app/node_modules
    ports:
      - "3000:3000"
    command: npm run dev

Best Practices

1. Use multi-stage builds to minimize image size
2. Don't run as root — use USER instruction
3. Use .dockerignore to exclude unnecessary files
4. Pin image versions — avoid latest tag in production
5. Use healthchecks for container orchestration

Conclusion

Docker is essential for modern development. It ensures consistency across environments, simplifies deployment, and enables microservice architectures. Master Docker fundamentals and Docker Compose to streamline your development workflow.