Docker Containerization for Developers

Introduction

Docker enables consistent application deployment across different environments. This guide covers Docker essentials for developers.

What is Docker?

Docker packages your application and dependencies into a standardized unit called a container, ensuring it runs the same everywhere.

Dockerfile Structure

# Use official Node.js image as base
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 ["npm", "start"]

Docker Compose

Manage multi-container applications:

# docker-compose.yml
version: '3.8'
 
services:
  web:
    build: .
    ports:
      - "3000:3000"
    environment:
      - DATABASE_URL=postgres://db:5432/myapp
    depends_on:
      - db
 
  db:
    image: postgres:14-alpine
    environment:
      - POSTGRES_PASSWORD=password
      - POSTGRES_DB=myapp
    volumes:
      - postgres_data:/var/lib/postgresql/data
 
volumes:
  postgres_data:

Common Docker Commands

# Build image
docker build -t my-app:1.0 .
 
# Run container
docker run -p 3000:3000 my-app:1.0
 
# View running containers
docker ps
 
# View all containers
docker ps -a
 
# Stop container
docker stop container_id
 
# Remove image
docker rmi image_id
 
# View logs
docker logs container_id
 
# Execute command in container
docker exec -it container_id bash

Best Practices

Minimize Image Size

Use Alpine Linux base images
Remove build dependencies
Use multi-stage builds

# Multi-stage build
FROM node:18 AS builder
WORKDIR /app
COPY . .
RUN npm ci && npm run build
 
FROM node:18-alpine
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY package*.json ./
RUN npm ci --only=production
CMD ["npm", "start"]

Security

Use specific image versions (not latest)
Don't run as root
Scan for vulnerabilities
Use secrets for sensitive data

RUN addgroup -g 1001 -S nodejs
RUN adduser -S nodejs -u 1001
USER nodejs

Performance

Leverage layer caching
Order commands by change frequency
Use .dockerignore file

Container Networking

# Create network
docker network create my-network
 
# Run container on network
docker run --network my-network --name web my-app
 
# Another container can access it at 'http://web:3000'
docker run --network my-network another-app

Volumes for Data Persistence

# Named volume
docker run -v my-data:/app/data my-app
 
# Bind mount
docker run -v /path/on/host:/app/data my-app

Conclusion

Docker standardizes deployment and simplifies development workflows. Master containerization to streamline your development process.