Design a Global CDN With Edge Caching

Problem

Design a global CDN that caches and serves content from edge locations close to users.

Requirements

Functional:

• Cache static/dynamic content at edge PoPs
• Cache invalidation/purge
• Origin shielding on miss
• Honor cache-control headers

Non-functional:

• Millions of requests/sec globally
• Low latency, high cache-hit ratio
• DDoS-resilient

Discussion points

1. Edge PoP architecture and anycast routing
2. Cache hierarchy (edge -> regional -> origin shield)
3. Cache key design and invalidation
4. Request coalescing to protect origin
5. DDoS mitigation and rate limiting