Containerization - Docker & Kubernetes

Overview

Containerization packages applications with their dependencies in isolated, lightweight environments. This directory covers Docker for container management and Kubernetes for orchestration at scale.

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What is Containerization?

Containerization is a method of packaging applications along with their dependencies, libraries, and configuration files into isolated units called containers.

Key Benefits

• ✅ Consistency - Same behavior across dev, test, and production
• ✅ Portability - Run anywhere (laptop, cloud, on-premise)
• ✅ Efficiency - Lightweight compared to virtual machines
• ✅ Isolation - Applications don't interfere with each other
• ✅ Scalability - Easy to scale up or down
• ✅ Fast Deployment - Start in seconds, not minutes

Containers vs Virtual Machines

Feature	Containers	Virtual Machines
Size	MBs	GBs
Startup	Seconds	Minutes
Resource Usage	Low	High
Isolation	Process-level	OS-level
Portability	High	Medium
Performance	Near-native	Overhead

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Learning Path

Beginner Level - Docker Basics

1. Docker Fundamentals - Start here
2. What is Docker and containerization
3. Docker architecture (client-server model)
4. Container lifecycle
5. Docker commands overview
6. Volumes and networking basics

7. Docker Compose introduction

8. Docker Concepts

9. Why Docker exists
10. Images vs containers
11. Docker architecture
12. Image layers
13. Build vs run time

14. Container isolation

15. Installation

16. Installing Docker on various platforms
17. Docker Desktop setup
18. Verifying installation
19. Post-installation configuration

Intermediate Level - Docker Usage

1. Docker Commands
2. Essential Docker CLI commands
3. Container management
4. Image management
5. Network commands
6. Volume commands

7. Debugging and troubleshooting

8. Dockerfile

9. Dockerfile syntax and instructions
10. Building custom images
11. Multi-stage builds
12. Best practices

13. Optimization techniques

14. Docker Compose

15. Multi-container applications
16. docker-compose.yml syntax
17. Service definitions
18. Networks and volumes
19. Environment management
20. Common patterns

Advanced Level - Production

1. Advanced Topics
2. Security best practices
3. Performance optimization
4. Production deployment
5. Monitoring and logging
6. CI/CD integration
7. Troubleshooting

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Quick Reference

Essential Docker Commands

Container Management

# Run container
docker run -d --name myapp nginx

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

# Stop/Start/Restart
docker stop myapp
docker start myapp
docker restart myapp

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

# View logs
docker logs myapp
docker logs -f myapp         # Follow logs

# Execute command in container
docker exec -it myapp bash

Image Management

# List images
docker images

# Pull image
docker pull nginx:latest

# Build image
docker build -t myapp:1.0 .

# Tag image
docker tag myapp:1.0 username/myapp:1.0

# Push image
docker push username/myapp:1.0

# Remove image
docker rmi myapp:1.0

Docker Compose

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

# Stop services
docker compose down

# View logs
docker compose logs
docker compose logs -f       # Follow logs

# Execute command
docker compose exec web bash

# Rebuild services
docker compose up --build

Dockerfile Example

# Multi-stage build
FROM node:18-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production

FROM node:18-alpine
WORKDIR /app
COPY --from=builder /app/node_modules ./node_modules
COPY . .
EXPOSE 3000
CMD ["node", "server.js"]

Docker Compose Example

version: '3.8'

services:
  web:
    build: ./web
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=production
    depends_on:
      - db
    volumes:
      - ./web:/app
    networks:
      - app-network

  db:
    image: postgres:15-alpine
    environment:
      - POSTGRES_PASSWORD=secret
    volumes:
      - db-data:/var/lib/postgresql/data
    networks:
      - app-network

volumes:
  db-data:

networks:
  app-network:
    driver: bridge

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Docker Architecture

Components

┌─────────────────────────────────────────────────────────┐
│                    Docker Client                        │
│                   (docker CLI)                          │
└────────────────────┬────────────────────────────────────┘
                     │ REST API
┌────────────────────▼────────────────────────────────────┐
│                 Docker Daemon                           │
│                  (dockerd)                              │
│  ┌──────────┐  ┌──────────┐  ┌──────────┐            │
│  │ Images   │  │Containers│  │ Networks │            │
│  └──────────┘  └──────────┘  └──────────┘            │
│  ┌──────────┐  ┌──────────┐                           │
│  │ Volumes  │  │ Plugins  │                           │
│  └──────────┘  └──────────┘                           │
└────────────────────┬────────────────────────────────────┘
                     │
┌────────────────────▼────────────────────────────────────┐
│              Docker Registry                            │
│            (Docker Hub, Private)                        │
└─────────────────────────────────────────────────────────┘

Docker Client: CLI tool that sends commands to Docker daemon Docker Daemon: Background service that manages containers, images, networks, and volumes Docker Registry: Storage for Docker images (Docker Hub, private registries)

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Container Lifecycle

┌─────────┐
│ Created │  docker create
└────┬────┘
     │
     │ docker start
     ▼
┌─────────┐
│ Running │  docker run
└────┬────┘
     │
     ├─────► docker pause ──► ┌────────┐
     │                         │ Paused │
     │      docker unpause ◄── └────────┘
     │
     │ docker stop
     ▼
┌─────────┐
│ Stopped │
└────┬────┘
     │
     │ docker rm
     ▼
┌─────────┐
│ Deleted │
└─────────┘

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Docker Networking

Network Drivers

Driver	Description	Use Case
bridge	Default, isolated network	Single-host communication
host	Uses host network directly	Performance-critical apps
overlay	Multi-host networking	Docker Swarm, Kubernetes
macvlan	Assigns MAC address to container	Legacy app integration
none	No networking	Isolated containers

Network Commands

# Create network
docker network create mynetwork

# List networks
docker network ls

# Inspect network
docker network inspect mynetwork

# Connect container to network
docker network connect mynetwork mycontainer

# Disconnect
docker network disconnect mynetwork mycontainer

# Remove network
docker network rm mynetwork

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Docker Volumes

Volume Types

1. Named Volumes - Managed by Docker

   docker volume create mydata
   docker run -v mydata:/data myapp
   

2. Bind Mounts - Host directory mounted

   docker run -v /host/path:/container/path myapp
   

3. tmpfs Mounts - Temporary, in-memory

   docker run --tmpfs /tmp myapp
   

Volume Commands

# Create volume
docker volume create myvolume

# List volumes
docker volume ls

# Inspect volume
docker volume inspect myvolume

# Remove volume
docker volume rm myvolume

# Remove unused volumes
docker volume prune

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Best Practices

Image Building

• ✅ Use official base images
• ✅ Use specific tags, not latest
• ✅ Minimize layers (combine RUN commands)
• ✅ Use multi-stage builds
• ✅ Don't run as root user
• ✅ Use .dockerignore file
• ✅ Scan images for vulnerabilities
• ✅ Keep images small

Container Management

• ✅ One process per container
• ✅ Use environment variables for configuration
• ✅ Implement health checks
• ✅ Set resource limits (CPU, memory)
• ✅ Use volumes for persistent data
• ✅ Log to stdout/stderr
• ✅ Handle signals properly (SIGTERM)
• ✅ Use restart policies

Security

• ✅ Don't store secrets in images
• ✅ Use secrets management (Docker secrets, env vars)
• ✅ Run containers as non-root
• ✅ Use read-only filesystems when possible
• ✅ Limit container capabilities
• ✅ Keep images updated
• ✅ Scan for vulnerabilities
• ✅ Use trusted registries

Production

• ✅ Use orchestration (Kubernetes, Docker Swarm)
• ✅ Implement monitoring and logging
• ✅ Use health checks
• ✅ Implement graceful shutdown
• ✅ Use CI/CD pipelines
• ✅ Tag images with version numbers
• ✅ Document your setup
• ✅ Test disaster recovery

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Common Use Cases

Development Environment

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

Microservices

services:
  frontend:
    image: myapp/frontend:1.0
  backend:
    image: myapp/backend:1.0
  database:
    image: postgres:15
  cache:
    image: redis:7

CI/CD Pipeline

# Build
docker build -t myapp:${VERSION} .

# Test
docker run myapp:${VERSION} npm test

# Push
docker push myapp:${VERSION}

# Deploy
docker service update --image myapp:${VERSION} myservice

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Troubleshooting

Container Won't Start

# Check logs
docker logs container_name

# Inspect container
docker inspect container_name

# Check events
docker events

# Try interactive mode
docker run -it image_name /bin/bash

Network Issues

# Check network
docker network inspect bridge

# Test connectivity
docker exec container_name ping other_container

# Check ports
docker port container_name

Performance Issues

# Check resource usage
docker stats

# Check container processes
docker top container_name

# Inspect container details
docker inspect container_name

Image Issues

# Check image layers
docker history image_name

# Inspect image
docker inspect image_name

# Remove unused images
docker image prune

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Tools and Resources

Essential Tools

• Docker Desktop - GUI for Docker
• Docker Compose - Multi-container orchestration
• Docker Hub - Public image registry
• Portainer - Container management UI
• Dive - Image layer explorer
• Trivy - Vulnerability scanner

Monitoring

• Prometheus - Metrics collection
• Grafana - Visualization
• cAdvisor - Container metrics
• ELK Stack - Log aggregation

CI/CD Integration

• Jenkins - Automation server
• GitLab CI - Integrated CI/CD
• GitHub Actions - GitHub workflows
• CircleCI - Cloud CI/CD

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Directory Structure

CONTAINERIZATION/
├── README.md                      # This file
│
└── Docker/                        # Docker documentation
    ├── 0-Docker-Fundamentals.md   # Comprehensive basics
    ├── README.md                  # Docker concepts
    ├── 1-Installation.md          # Setup guide
    ├── 2-Docker-Commands.md       # CLI reference
    ├── 3-Dockerfile.md            # Image building
    ├── 4-Docker-Compose.md        # Multi-container apps
    ├── 5-Advanced-Topics.md       # Production topics
    ├── image.png                  # Architecture diagram
    ├── image 1.png                # Lifecycle diagram
    └── image 2.png                # States diagram

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Next Steps

After Learning Docker

1. Kubernetes - Container orchestration at scale
2. Docker Swarm - Docker's native orchestration
3. Service Mesh - Istio, Linkerd for microservices
4. CI/CD - Automate build and deployment
5. Monitoring - Prometheus, Grafana setup
6. Security - Container security best practices

Related Topics

• DevOps Core - Main documentation
• CI/CD - Continuous integration and deployment
• Observability - Monitoring containers
• Networking - Network fundamentals

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Last Updated: January 2026 Maintained by: DevOps Documentation Team