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Docker Fundamentals

🎯 Introduction

Docker is a platform for developing, shipping, and running applications in containers. Containers package applications with all dependencies, ensuring consistency across environments.

📚 Core Concepts

Container vs Virtual Machine

Virtual Machine:
┌─────────────────────────────────┐
│        Application              │
│        Bins/Libs                │
│        Guest OS                 │
│    ┌──────────────────────┐    │
│    │   Hypervisor         │    │
│    └──────────────────────┘    │
│        Host OS                  │
│        Infrastructure           │
└─────────────────────────────────┘

Container:
┌─────────────────────────────────┐
│        Application              │
│        Bins/Libs                │
│    ┌──────────────────────┐    │
│    │   Docker Engine      │    │
│    └──────────────────────┘    │
│        Host OS                  │
│        Infrastructure           │
└─────────────────────────────────┘

🐳 Installation

Ubuntu/Debian

# Update packages
sudo apt update

# Install prerequisites
sudo apt install -y ca-certificates curl gnupg lsb-release

# Add Docker's official GPG key
sudo mkdir -p /etc/apt/keyrings
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | \
    sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg

# Add Docker repository
echo \
  "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu \
  $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

# Install Docker
sudo apt update
sudo apt install -y docker-ce docker-ce-cli containerd.io docker-compose-plugin

# Start Docker
sudo systemctl start docker
sudo systemctl enable docker

# Add user to docker group
sudo usermod -aG docker $USER

Verify Installation

docker --version
docker run hello-world

🔧 Basic Commands

Images

# Pull image
docker pull nginx:latest
docker pull ubuntu:20.04

# List images
docker images
docker image ls

# Remove image
docker rmi nginx
docker image rm nginx

# Search images
docker search nginx

# Inspect image
docker inspect nginx

Containers

# Run container
docker run nginx
docker run -d nginx                    # Detached mode
docker run -it ubuntu bash             # Interactive
docker run -p 8080:80 nginx            # Port mapping
docker run -v /host:/container nginx   # Volume mount

# List containers
docker ps                               # Running
docker ps -a                            # All

# Stop container
docker stop container_id

# Start container
docker start container_id

# Remove container
docker rm container_id
docker rm -f container_id               # Force remove

# Execute command in container
docker exec -it container_id bash

# View logs
docker logs container_id
docker logs -f container_id             # Follow logs

# Container stats
docker stats
docker stats container_id

📝 Dockerfile

Basic Dockerfile

# Use base image
FROM ubuntu:20.04

# Set working directory
WORKDIR /app

# Set environment variables
ENV DEBIAN_FRONTEND=noninteractive

# Install dependencies
RUN apt update && \
    apt install -y nginx && \
    apt clean && \
    rm -rf /var/lib/apt/lists/*

# Copy files
COPY index.html /var/www/html/

# Expose port
EXPOSE 80

# Set command
CMD ["nginx", "-g", "daemon off;"]

Multi-stage Build

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

# Production stage
FROM nginx:alpine
COPY --from=builder /app/dist /usr/share/nginx/html
EXPOSE 80
CMD ["nginx", "-g", "daemon off;"]

Best Practices

  1. Use specific tags: node:18 not node:latest
  2. Minimize layers: Combine RUN commands
  3. Use .dockerignore: Exclude unnecessary files
  4. Multi-stage builds: Reduce image size
  5. Non-root user: Security best practice
  6. Health checks: Monitor container health
  7. Cache layers: Optimize build speed

🏗️ Docker Compose

docker-compose.yml

version: '3.8'

services:
  web:
    image: nginx:alpine
    ports:
      - "8080:80"
    volumes:
      - ./html:/usr/share/nginx/html
    depends_on:
      - app
  
  app:
    build: .
    environment:
      - DATABASE_URL=postgresql://db:5432/mydb
    depends_on:
      - db
  
  db:
    image: postgres:14
    environment:
      - POSTGRES_DB=mydb
      - POSTGRES_USER=user
      - POSTGRES_PASSWORD=password
    volumes:
      - db_data:/var/lib/postgresql/data

volumes:
  db_data:

Compose Commands

# Start services
docker-compose up
docker-compose up -d              # Detached

# Stop services
docker-compose down

# Build and start
docker-compose up --build

# View logs
docker-compose logs
docker-compose logs -f web

# Execute command
docker-compose exec web bash

🔐 Security Best Practices

  1. Use official images: From trusted sources
  2. Scan images: For vulnerabilities
  3. Non-root user: Don't run as root
  4. Minimal base images: Alpine Linux
  5. Secrets management: Don't hardcode secrets
  6. Regular updates: Keep images updated
  7. Network policies: Limit container communication

📊 Docker Networking

Network Types

# Bridge (default)
docker network create mynetwork
docker run --network mynetwork nginx

# Host
docker run --network host nginx

# None
docker run --network none nginx

Network Commands

# List networks
docker network ls

# Inspect network
docker network inspect bridge

# Connect container to network
docker network connect mynetwork container_id

# Disconnect
docker network disconnect mynetwork container_id

💾 Volumes

Volume Types

# Named volume
docker volume create myvolume
docker run -v myvolume:/data nginx

# Bind mount
docker run -v /host/path:/container/path nginx

# Anonymous volume
docker run -v /data nginx

Volume Commands

# List volumes
docker volume ls

# Inspect volume
docker volume inspect myvolume

# Remove volume
docker volume rm myvolume

🎯 Common Use Cases

Development Environment

version: '3.8'
services:
  app:
    build: .
    volumes:
      - .:/app
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=development

Production Deployment

version: '3.8'
services:
  app:
    image: myapp:latest
    restart: always
    ports:
      - "80:3000"
    environment:
      - NODE_ENV=production

✅ Mastery Checklist

  • Install and configure Docker
  • Build Docker images
  • Run and manage containers
  • Write Dockerfiles
  • Use Docker Compose
  • Manage volumes and networks
  • Understand security best practices
  • Optimize image size
  • Debug container issues
  • Deploy containers to production

Next: Learn about container orchestration with Kubernetes.