Content Delivery Networks (CDN) Cheat Sheet: Optimizing Content Delivery Worldwide

Introduction: What is a CDN and Why It Matters

A Content Delivery Network (CDN) is a geographically distributed group of servers that work together to provide fast delivery of internet content. CDNs store cached versions of website content in multiple locations around the world, allowing users to access the content from servers closest to them.

Why CDNs Matter:

• Speed: Reduce page load times by serving content from nearby servers
• Reliability: Distribute traffic across multiple servers to handle high loads
• Security: Provide protection against common cyber attacks like DDoS
• Scalability: Easily handle traffic spikes without infrastructure changes
• Cost Efficiency: Reduce origin server load and bandwidth costs

Core CDN Concepts & Principles

Edge Servers

• Distributed server networks positioned at “edges” of the internet
• Located at internet exchange points where different networks connect
• Cache and deliver content to users in their geographic vicinity

Content Caching

• Static Caching: Stores unchanging files (images, CSS, JS)
• Dynamic Caching: Stores content that changes occasionally
• Cache Invalidation: Process of removing outdated content from cache

Origin Servers

• The original server where your website or application is hosted
• CDN pulls content from origin when not in cache or when cache expires

Request Routing

• Technology that directs user requests to the optimal edge server
• Uses factors like geographic proximity, server load, and content availability

Time To Live (TTL)

• Duration that content remains cached before being refreshed
• Shorter TTL = fresher content but more origin requests
• Longer TTL = better performance but potentially stale content

Implementing a CDN: Step-by-Step Process

1. Assess Requirements
   • Identify content types that would benefit from CDN delivery
   • Determine geographic regions to prioritize
   • Calculate expected traffic volumes
2. Select CDN Provider
   • Compare features, pricing, and performance
   • Consider geographic coverage relevant to your audience
   • Review security offerings and integration capabilities
3. Configure DNS
   • Update DNS settings to route traffic through the CDN
   • Set up CNAME records pointing to CDN provider’s domain
   • Configure TTL settings for DNS records
4. Set Up Origins
   • Define origin server(s) in CDN dashboard
   • Configure origin pull settings and authentication
   • Set up backup origins for failover
5. Configure Caching Rules
   • Define cache TTL for different content types
   • Set cache headers appropriately
   • Configure cache key settings
6. Implement Security Features
   • Set up SSL/TLS certificates
   • Configure WAF (Web Application Firewall) if available
   • Set up token authentication for protected content
7. Test Performance
   • Verify content delivery from edge locations
   • Measure load times before and after implementation
   • Test cache hit ratios and origin offload
8. Monitor and Optimize
   • Track performance metrics (latency, cache hit ratio)
   • Identify opportunities to improve caching efficiency
   • Adjust settings based on real-world performance

Key CDN Techniques, Tools, and Methods

Content Optimization Techniques

• File Compression: Automatic Gzip/Brotli compression of text-based assets
• Image Optimization: Auto-conversion to efficient formats (WebP, AVIF)
• Minification: Removal of unnecessary code characters from CSS/JS
• HTTP/2 & HTTP/3: Multiplexed connections for faster parallel downloads
• Prefetching: Predictive loading of resources before they’re requested

Security Features

• DDoS Protection: Traffic filtering and absorption of attack traffic
• WAF (Web Application Firewall): Protection against common exploits
• Bot Management: Identification and filtering of malicious bot traffic
• Rate Limiting: Protection against brute force and abuse attempts
• Token Authentication: Secure access to protected content

Analytics and Monitoring Tools

• Real-time Log Analysis: Access to delivery logs for troubleshooting
• Performance Dashboards: Visualization of key metrics
• Cache Analytics: Insights into cache hit ratios and efficiency
• Traffic Reports: Detailed information about visitor patterns
• Error Tracking: Identification of delivery failures and status codes

Edge Computing Capabilities

• Edge Functions/Workers: Run code at the edge without managing servers
• Edge Redirects: Configure URL redirects at the edge level
• A/B Testing: Implement testing logic at the CDN layer
• Personalization: Tailor content based on user location or other factors

CDN Provider Comparison

Common CDN Challenges and Solutions

High Cache Miss Ratio

• Problem: Too many requests hitting origin server
• Solutions:
  • Increase TTL for static content
  • Implement stale-while-revalidate cache control
  • Optimize cache key configuration
  • Review which query parameters affect caching

SSL/TLS Configuration Issues

• Problem: Certificate errors or mixed content warnings
• Solutions:
  • Ensure proper SSL certificate installation
  • Configure automatic HTTP to HTTPS redirects
  • Use relative URLs for resources where possible
  • Implement content security policies

Cache Invalidation Delays

• Problem: Updated content not appearing immediately
• Solutions:
  • Implement versioned URLs for content updates
  • Use targeted purge requests instead of global cache clears
  • Configure smart purging based on content tags
  • Consider lower TTLs for frequently changing content

Cost Management

• Problem: Unexpected or high CDN costs
• Solutions:
  • Optimize caching efficiency to reduce origin pulls
  • Use bandwidth reduction features (compression, image optimization)
  • Set up billing alerts and monitoring
  • Consider reserved capacity plans for predictable traffic

Performance Variations

• Problem: Inconsistent global performance
• Solutions:
  • Review edge server coverage in key markets
  • Test from multiple geographic locations
  • Implement point-of-presence (PoP) selection logic
  • Consider multi-CDN approach for critical applications

CDN Best Practices and Tips

Caching Strategy

• Cache static assets with long TTLs (1 year+) with versioned URLs
• Implement cache control headers at the origin server
• Use appropriate cache keys to maximize cache hit ratio
• Configure different caching rules based on content type and freshness needs

Security Implementation

• Enable HTTPS for all content delivery
• Implement modern security headers (CSP, HSTS)
• Configure appropriate CORS policies
• Use signed URLs or tokens for sensitive content

Performance Optimization

• Leverage browser caching alongside CDN caching
• Implement preconnect and dns-prefetch resource hints
• Configure HTTP/2 or HTTP/3 delivery where available
• Use CDN-specific performance features (e.g., Railgun, Argo)

Operational Efficiency

• Automate CDN configuration using Infrastructure as Code
• Implement robust monitoring and alerting for CDN metrics
• Develop clear cache invalidation procedures for content updates
• Maintain documentation of CDN architecture and configurations

Multi-CDN Strategy

• Consider using multiple CDNs for critical applications
• Implement load balancing between CDNs
• Use consistent configuration across providers
• Test failover scenarios regularly

Resources for Further Learning

Documentation and Guides

• MDN Web Docs: HTTP Caching
• Web.dev: Content Delivery Networks
• Cloudflare Learning Center
• AWS CDN Best Practices

Tools

• WebPageTest – Test CDN performance from global locations
• Catchpoint – CDN monitoring and testing
• KeyCDN Tools – Collection of CDN testing utilities
• CDNPerf – CDN performance comparison

Books and Courses

• “High Performance Browser Networking” by Ilya Grigorik
• “HTTP/2 in Action” by Barry Pollard
• Udemy: “Content Delivery Networks (CDN) Fundamentals”
• Coursera: “Cloud Computing Specialization” (includes CDN modules)

Forums and Communities

• Stack Overflow: CDN Tag
• Reddit r/webdev
• Web Performance Slack Community