Docker and Containerization Fundamentals

Docker has revolutionized how we develop, ship, and run applications. In this post, we’ll explore the core concepts of containerization and Docker.

What is Docker?

Docker is a platform for developing, shipping, and running applications in containers. Containers are lightweight, portable, and self-sufficient units that can run applications and their dependencies.

Why Use Docker?

1. Consistency

• Same environment from development to production
• No more “works on my machine” issues

2. Isolation

• Applications run in their own containers
• Dependencies don’t conflict with each other

3. Portability

• Run anywhere Docker runs
• Easy deployment across different platforms

Basic Docker Commands

# Build an image
docker build -t my-app .

# Run a container
docker run -d -p 8080:8080 my-app

# List running containers
docker ps

# Stop a container
docker stop container_id

# Remove a container
docker rm container_id

Dockerfile Example

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

# Set working directory
WORKDIR /app

# Copy package files
COPY package*.json ./

# Install dependencies
RUN npm install

# Copy application code
COPY . .

# Expose port
EXPOSE 3000

# Start the application
CMD ["npm", "start"]

Docker Compose for Multi-Container Apps

version: '3.8'
services:
  web:
    build: .
    ports:
      - "3000:3000"
    depends_on:
      - db

  db:
    image: postgres:13
    environment:
      POSTGRES_DB: myapp
      POSTGRES_USER: user
      POSTGRES_PASSWORD: password
    volumes:
      - postgres_data:/var/lib/postgresql/data

volumes:
  postgres_data:

Best Practices

1. Use Multi-Stage Builds: Reduce image size by using multiple build stages
2. Don’t Run as Root: Create non-root users for security
3. Use .dockerignore: Exclude unnecessary files from build context
4. Tag Images Properly: Use semantic versioning for image tags
5. Keep Images Small: Use alpine images and clean up cache

Docker vs Virtual Machines

Docker containers provide a lightweight, efficient way to package and deploy applications, making them ideal for modern development workflows.