Intermediate

CDN & Edge Caching

Caching Patterns

Serve static and cacheable dynamic content from edge POPs for lower latency

Core Idea

Use globally distributed edge caches and HTTP caching semantics to deliver content close to users. Combine with edge compute for rewrites, image optimization, and security enforcement.

When to Use

When you have global users, large static content, or want to offload origin and reduce egress/latency.

Recognition Cues
Indicators that this pattern might be the right solution
  • High TTFB for far-away users
  • Origin bandwidth/egress costs are high
  • Traffic spikes overload origin
  • Static assets or cacheable dynamic pages

Pattern Variants & Approaches

Overview
Clients fetch from edge POPs; cache hits serve immediately, misses fetch from origin which queries backing stores.

Overview Architecture

GETMiss/BypassQuery👤Client⚡CDN/Edge Cache🖥️Origin💾Database

When to Use This Variant

  • Global users and static assets
  • High egress costs at origin
  • Need WAF/DoS protection at edge

Use Case

Static websites, media delivery, cacheable dynamic pages with personalization controls.

Advantages

  • Lower TTFB and origin load
  • Tiered caching and shielding
  • Edge security controls

Implementation Example

# Example headers
Cache-Control: public, max-age=600
ETag: "content-hash"
Vary: Accept-Encoding, Authorization
Tradeoffs

Pros

  • Lower latency and higher throughput
  • Origin offload and egress savings
  • DDoS protection and WAF closer to users
  • Edge compute for dynamic personalization

Cons

  • Potential staleness and invalidation complexity
  • Debugging multi-layer caches is harder
  • Vendor lock-in for proprietary features
  • Extra layer adds failure modes
Common Pitfalls
  • Incorrect Cache-Control/ETag usage
  • Caching personalized or private data by accident
  • Missing Vary headers (auth, language, device)
  • Slow or missing purge/invalidation pipeline
  • Stampede on cache purge or miss
Design Considerations
  • Explicit caching headers, ETag/Last-Modified
  • Origin shield and tiered caching
  • Signed URLs/cookies and tokenized access
  • Image/video transforms and compression at edge
  • Purge APIs, soft TTL, and pre-warming
Real-World Examples
Cloudflare

Global anycast CDN with edge workers

300+ cities; massive throughput
Akamai

Enterprise CDN for media and software

Exabyte-scale monthly delivery
Netflix

Open Connect peering caches closer to ISPs

World's largest video CDN
Complexity Analysis
Scalability

Global POPs - Anycast network

Implementation Complexity

Medium - Multi-layer cache semantics

Cost

Low to Medium - Offsets origin costs

Related Patterns
Caching StrategiesAPI GatewayRate LimitingEdge Compute