🐋 Docker Containerization Guide

1. Docker Overview

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

2. Installation

2.1 Ubuntu/Debian

# Update package index
sudo apt update

# Install dependencies
sudo apt install -y apt-transport-https ca-certificates curl software-properties-common

# Add Docker GPG key
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg

# Add Docker repository
echo "deb [arch=amd64 signed-by=/usr/share/keyrings/docker-archive-keyring.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

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

# Verify installation
docker --version
docker run hello-world

2.2 RHEL/CentOS

# Install using yum
sudo yum install -y yum-utils
sudo yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
sudo yum install docker-ce docker-ce-cli containerd.io docker-compose-plugin
sudo systemctl start docker
sudo systemctl enable docker

3. Essential Docker Commands

3.1 Container Lifecycle

# Run a container
docker run nginx                    # Run nginx
docker run -d nginx                 # Detached mode
docker run -d -p 8080:80 nginx     # Port mapping
docker run -d --name my-nginx nginx # Named container
docker run -it ubuntu bash          # Interactive terminal

# List containers
docker ps                           # Running containers
docker ps -a                        # All containers
docker ps -q                        # Only IDs

# Stop/start containers
docker stop container_id
docker start container_id
docker restart container_id

# Remove containers
docker rm container_id
docker rm -f container_id           # Force remove running
docker container prune              # Remove all stopped

# Execute commands in running container
docker exec -it container_id bash
docker exec container_id ls /app

3.2 Image Management

# Pull images
docker pull nginx
docker pull nginx:1.21
docker pull ubuntu:22.04

# List images
docker images
docker image ls

# Remove images
docker rmi image_id
docker image prune                  # Remove unused images
docker image prune -a              # Remove all unused

# Tag images
docker tag nginx:latest myrepo/nginx:v1.0

# Push to registry
docker push myrepo/nginx:v1.0

# Search images
docker search nginx

# Inspect image
docker inspect nginx
docker history nginx

3.3 Container Operations

# View logs
docker logs container_id
docker logs -f container_id         # Follow logs
docker logs --tail 100 container_id # Last 100 lines

# View stats
docker stats
docker stats container_id

# Inspect container
docker inspect container_id

# Copy files
docker cp file.txt container_id:/app/
docker cp container_id:/app/file.txt ./

# View port mappings
docker port container_id

4. Dockerfile Best Practices

4.1 Basic Dockerfile

# Use official base image
FROM node:18-alpine

# Set working directory
WORKDIR /app

# Copy package files
COPY package*.json ./

# Install dependencies
RUN npm install --production

# Copy application code
COPY . .

# Expose port
EXPOSE 3000

# Set environment variables
ENV NODE_ENV=production

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

4.2 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 node:18-alpine
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
COPY package*.json ./
EXPOSE 3000
CMD ["node", "dist/server.js"]

4.3 Python Application

FROM python:3.11-slim

WORKDIR /app

# Install dependencies
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

# Copy application
COPY . .

# Create non-root user
RUN useradd -m -u 1000 appuser && \
    chown -R appuser:appuser /app
USER appuser

EXPOSE 8000

CMD ["python", "app.py"]

4.4 Build and Run

# Build image
docker build -t myapp:latest .
docker build -t myapp:v1.0 -f Dockerfile.prod .

# Build with build args
docker build --build-arg VERSION=1.0 -t myapp .

# Run built image
docker run -d -p 3000:3000 --name myapp myapp:latest

5. Docker Volumes and Data Persistence

5.1 Volume Types

# Named volumes (recommended)
docker volume create mydata
docker run -d -v mydata:/app/data nginx

# Bind mounts (local directory)
docker run -d -v /host/path:/container/path nginx
docker run -d -v $(pwd):/app node:18

# tmpfs (temporary, in memory)
docker run -d --tmpfs /app/cache nginx

5.2 Volume Management

# List volumes
docker volume ls

# Inspect volume
docker volume inspect mydata

# Remove volume
docker volume rm mydata

# Remove unused volumes
docker volume prune

# Backup volume
docker run --rm -v mydata:/data -v $(pwd):/backup alpine tar czf /backup/backup.tar.gz /data

# Restore volume
docker run --rm -v mydata:/data -v $(pwd):/backup alpine tar xzf /backup/backup.tar.gz -C /

6. Docker Networking

6.1 Network Types

# Create custom network
docker network create mynetwork

# List networks
docker network ls

# Run container on network
docker run -d --network mynetwork --name web nginx
docker run -d --network mynetwork --name db postgres

# Inspect network
docker network inspect mynetwork

# Remove network
docker network rm mynetwork

6.2 Network Modes

# Bridge (default)
docker run -d nginx

# Host network (container uses host network)
docker run -d --network host nginx

# None (no networking)
docker run -d --network none nginx

# Connect to existing container's network
docker run -d --network container:web alpine

6.3 Port Publishing

# Publish single port
docker run -d -p 8080:80 nginx

# Publish all exposed ports
docker run -d -P nginx

# Publish to specific host IP
docker run -d -p 127.0.0.1:8080:80 nginx

# Publish multiple ports
docker run -d -p 80:80 -p 443:443 nginx

7. Docker Compose

7.1 Basic docker-compose.yml

version: '3.8'

services:
  web:
    image: nginx:latest
    ports:
      - "80:80"
    volumes:
      - ./html:/usr/share/nginx/html
    networks:
      - webnet
    restart: unless-stopped

  app:
    build: ./app
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=production
      - DB_HOST=db
    depends_on:
      - db
    networks:
      - webnet

  db:
    image: postgres:15
    volumes:
      - pgdata:/var/lib/postgresql/data
    environment:
      - POSTGRES_PASSWORD=secretpass
      - POSTGRES_DB=myapp
    networks:
      - webnet

networks:
  webnet:
    driver: bridge

volumes:
  pgdata:

7.2 Compose Commands

# Start services
docker compose up
docker compose up -d                # Detached mode
docker compose up --build           # Rebuild images

# Stop services
docker compose down                 # Stop and remove
docker compose down -v              # Remove volumes too
docker compose stop                 # Stop without removing

# View logs
docker compose logs
docker compose logs -f web          # Follow specific service

# Scale services
docker compose up -d --scale app=3

# Execute command
docker compose exec web bash
docker compose exec db psql -U postgres

# View running services
docker compose ps

8. Best Practices

8.1 .dockerignore Example

# .dockerignore
node_modules
npm-debug.log
.git
.gitignore
README.md
.env
.env.local
dist
coverage
.vscode
.idea
*.md

8.2 Security Scanning

# Scan image for vulnerabilities
docker scan myapp:latest

# Use Trivy for scanning
docker run aquasec/trivy image myapp:latest

# Scan with Snyk
snyk container test myapp:latest

9. Troubleshooting

9.1 Common Issues

9.2 Cleanup Commands

# Remove all stopped containers
docker container prune

# Remove all unused images
docker image prune -a

# Remove all unused volumes
docker volume prune

# Remove all unused networks
docker network prune

# Remove everything unused
docker system prune -a --volumes

# View disk usage
docker system df
docker system df -v

10. Additional Resources

• Official Docker Documentation
• Docker Hub
• Awesome Docker Compose Examples
• Docker Development Best Practices