The Ultimate Network & DevOps Reference Cheatsheet

# SSL/TLS debugging commands

# Check certificate details
openssl s_client -connect example.com:443 -servername example.com
openssl x509 -in cert.pem -text -noout

# Check certificate expiration
echo | openssl s_client -connect example.com:443 2>/dev/null | \
  openssl x509 -noout -dates

# Generate self-signed certificate
openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem \
  -days 365 -nodes -subj "/CN=localhost"

# Generate CSR (Certificate Signing Request)
openssl req -newkey rsa:2048 -nodes -keyout domain.key \
  -out domain.csr -subj "/CN=example.com"

# Certbot (Let's Encrypt)
sudo certbot certonly --standalone -d example.com -d www.example.com
sudo certbot renew --dry-run
sudo certbot install --nginx -d example.com

# Docker Compose v2+ reference
version: "3.9"

services:
  app:
    image: node:20-alpine
    working_dir: /app
    command: npm run start
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=production
      - DB_HOST=db
    env_file:
      - .env
    volumes:
      - .:/app
      - node_modules:/app/node_modules
    depends_on:
      db:
        condition: service_healthy
    restart: unless-stopped
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost:3000/health"]
      interval: 30s
      timeout: 10s
      retries: 3
      start_period: 40s
    deploy:
      resources:
        limits:
          cpus: "0.5"
          memory: 512M
    networks:
      - frontend
      - backend

  db:
    image: postgres:16-alpine
    environment:
      POSTGRES_DB: myapp
      POSTGRES_USER: admin
      POSTGRES_PASSWORD: secret
    volumes:
      - pgdata:/var/lib/postgresql/data
    ports:
      - "5432:5432"
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U admin"]
      interval: 10s
      timeout: 5s
      retries: 5
    networks:
      - backend

  nginx:
    image: nginx:alpine
    ports:
      - "80:80"
      - "443:443"
    volumes:
      - ./nginx.conf:/etc/nginx/nginx.conf
      - ./ssl:/etc/nginx/ssl
    depends_on:
      - app
    networks:
      - frontend

volumes:
  node_modules:
  pgdata:

networks:
  frontend:
    driver: bridge
  backend:
    driver: bridge
    internal: true  # no external access

# GitHub Actions - CI/CD Pipeline
name: CI/CD Pipeline
on:
  push:
    branches: [main, develop]
  pull_request:
    branches: [main]

jobs:
  test:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        node-version: [18, 20]
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: ${{ matrix.node-version }}
          cache: 'npm'
      - run: npm ci
      - run: npm run lint
      - run: npm run test
      - run: npm run build

  deploy:
    needs: test
    runs-on: ubuntu-latest
    if: github.ref == 'refs/heads/main'
    steps:
      - uses: actions/checkout@v4
      - name: Deploy to production
        run: |
          echo "Deploying to production..."
          # Add deployment commands here

# .gitignore essential entries
.env
.env.local
.env.*.local
node_modules/
dist/
build/
.next/
.DS_Store
*.log
coverage/
.vscode/
.idea/
*.pem
*.key
credentials.json
secrets.yml

# Common Prometheus / Grafana Queries (PromQL)

# HTTP request rate (requests/sec)
rate(http_requests_total[5m])

# 95th percentile latency
histogram_quantile(0.95, rate(http_request_duration_seconds_bucket[5m]))

# CPU usage by container
rate(container_cpu_usage_seconds_total{name="myapp"}[5m]) * 100

# Memory usage percentage
container_memory_usage_bytes{name="myapp"} / container_spec_memory_limit_bytes{name="myapp"} * 100

# Error rate percentage
rate(http_requests_total{status=~"5.."}[5m]) / rate(http_requests_total[5m]) * 100

# Uptime (time since last restart)
time() - process_start_time_seconds