Docker Containerization

Blogger6/15/24About 3 min

Docker Containerization

Overview

Docker is an open-source containerization platform for packaging applications and their dependencies into containers for cross-platform deployment.

1. Installation and Configuration

1.1 Install Docker (Linux)

# Update system
sudo apt-get update
sudo apt-get upgrade -y

# Install dependencies
sudo apt-get install -y \
    apt-transport-https \
    ca-certificates \
    curl \
    gnupg \
    lsb-release

# 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=$(dpkg --print-architecture) 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-get update
sudo apt-get install -y docker-ce docker-ce-cli containerd.io

# Start Docker service
sudo systemctl start docker
sudo systemctl enable docker

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

1.2 Basic Docker Commands

# View Docker info
docker info

# List images
docker images

# List containers
docker ps -a

# Pull image
docker pull nginx:latest

# Run container
docker run -d -p 80:80 nginx

# Enter container
docker exec -it container_id /bin/bash

# View container logs
docker logs container_id

# Stop container
docker stop container_id

# Remove container
docker rm container_id

# Remove image
docker rmi image_id

2. Writing Dockerfiles

2.1 .NET Application Dockerfile

# Use official .NET SDK image as build stage
FROM mcr.microsoft.com/dotnet/sdk:8.0 AS build-env
WORKDIR /app

# Copy project files
COPY *.csproj ./
RUN dotnet restore

# Copy all code and build
COPY . ./
RUN dotnet publish -c Release -o out

# Use official .NET runtime image
FROM mcr.microsoft.com/dotnet/aspnet:8.0
WORKDIR /app
COPY --from=build-env /app/out .

# Expose ports
EXPOSE 80
EXPOSE 443

# Set environment variables
ENV ASPNETCORE_URLS=http://+:80

# Start application
ENTRYPOINT ["dotnet", "MyApp.dll"]

2.2 Multi-Stage Build Optimization

# Build stage
FROM node:20 AS frontend-build
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . ./
RUN npm run build

# Runtime stage
FROM nginx:alpine
COPY --from=frontend-build /app/dist /usr/share/nginx/html
COPY nginx.conf /etc/nginx/nginx.conf
EXPOSE 80
CMD ["nginx", "-g", "daemon off;"]

2.3 Dockerfile Best Practices

Technique	Description
Use multi-stage builds	Reduce image size
Layer caching	Place unchanged layers first
Use .dockerignore	Exclude unnecessary files
Use non-root user	Improve security
Set HEALTHCHECK	Monitor container health

# .dockerignore
node_modules
npm-debug.log
.git
dist

3. Docker Compose

3.1 docker-compose.yml Example

version: '3.8'

services:
  web:
    build: .
    ports:
      - "80:80"
    depends_on:
      - db
      - redis
    environment:
      - ConnectionStrings__DefaultConnection=Server=db;Database=MyDb;User ID=sa;Password=Password123;
      - Redis__ConnectionString=redis:6379

  db:
    image: mcr.microsoft.com/mssql/server:2022-latest
    environment:
      - SA_PASSWORD=Password123
      - ACCEPT_EULA=Y
    volumes:
      - sql_data:/var/opt/mssql

  redis:
    image: redis:latest
    volumes:
      - redis_data:/data
    ports:
      - "6379:6379"

volumes:
  sql_data:
  redis_data:

3.2 Common Commands

# Start services
docker-compose up -d

# View logs
docker-compose logs -f

# Stop services
docker-compose down

# Rebuild and start
docker-compose up -d --build

# View service status
docker-compose ps

# Enter container
docker-compose exec web /bin/bash

4. Network Configuration

4.1 Create a Custom Network

# Create network
docker network create my-network

# List networks
docker network ls

# Connect container to network
docker network connect my-network container_name

4.2 Docker Compose Networks

version: '3.8'

services:
  web:
    build: .
    networks:
      - frontend
      - backend

  api:
    build: ./api
    networks:
      - backend

  db:
    image: mysql
    networks:
      - backend

networks:
  frontend:
    driver: bridge
  backend:
    driver: bridge

5. Data Persistence

5.1 Using Volumes

# Create volume
docker volume create my-volume

# List volumes
docker volume ls

# Run container with volume mount
docker run -d -v my-volume:/app/data nginx

5.2 Mount Host Directories

# Mount host directory to container
docker run -d -v /host/path:/container/path nginx

# Read-only mount
docker run -d -v /host/path:/container/path:ro nginx

6. Docker Image Management

6.1 Build Images

# Build image
docker build -t my-app:1.0.0 .

# Pass build arguments
docker build --build-arg ENV=production -t my-app:1.0.0 .

6.2 Push Images to Registry

# Log in to Docker Hub
docker login

# Tag image
docker tag my-app:1.0.0 username/my-app:1.0.0

# Push image
docker push username/my-app:1.0.0

6.3 Use a Private Registry

# Start private registry
docker run -d -p 5000:5000 --name registry registry:2

# Tag image
docker tag my-app:1.0.0 localhost:5000/my-app:1.0.0

# Push image
docker push localhost:5000/my-app:1.0.0

# Pull image
docker pull localhost:5000/my-app:1.0.0

7. Security Best Practices

7.1 Image Security

# Scan image for vulnerabilities
docker scan my-app:1.0.0

# Use non-root user
RUN useradd -m appuser
USER appuser

# Minimize image
FROM alpine:latest

7.2 Container Security

# Limit container resources
docker run --memory=512m --cpus=2 nginx

# Read-only filesystem
docker run --read-only nginx

# Disable privileged mode
docker run --privileged=false nginx

8. Monitoring and Logging

8.1 View Logs

# View container logs
docker logs container_id

# Follow logs in real time
docker logs -f container_id

# View last N lines of logs
docker logs --tail 100 container_id

8.2 Container Monitoring

# View container resource usage
docker stats

# View container details
docker inspect container_id

9. Docker Swarm Cluster

9.1 Initialize Swarm

# Initialize Swarm
docker swarm init

# Add worker node
docker swarm join --token token manager_ip:2377

9.2 Deploy Services

# docker-compose.yml
version: '3.8'

services:
  web:
    image: my-app:1.0.0
    deploy:
      replicas: 3
      restart_policy:
        condition: on-failure
      resources:
        limits:
          memory: 512M
        reservations:
          memory: 256M
    ports:
      - "80:80"

# Deploy service
docker stack deploy -c docker-compose.yml my-stack

# View services
docker stack services my-stack

# Scale service
docker service scale my-stack_web=5

Summary

Docker containerization simplifies application deployment and operations, improving development efficiency and system reliability. Mastering Docker is an essential skill for modern DevOps engineers.

Author: Lei Tao
Date: June 15, 2024