Design a Content Delivery Network (CDN)

Question

Design a global CDN for static and dynamic content delivery, cache invalidation, SSL termination, and DDoS protection.

Accepted Answer

Designing a global CDN for static and dynamic content requires a multi-layered approach, balancing performance, reliability, and security. Our solution would leverage a distributed architecture with intelligent caching and robust security measures to ensure optimal content delivery worldwide. **Edge Points of Presence (PoPs):** We would strategically deploy a globally distributed network of Edge PoPs, located geographically close to end-users, to minimize latency. These PoPs would house caching servers, SSL termination capabilities, and initial DDoS mitigation layers. The selection of PoP locations would be data-driven, considering user demographics, internet exchange points, and existing infrastructure. **Cache Hierarchy and Consistent Hashing:** A hierarchical caching strategy would be implemented. Primary caches would reside at the Edge PoPs for ultra-low latency. A secondary tier of regional caches would handle cache misses from multiple Edge PoPs, improving cache hit ratios. For distributing cache objects and managing dynamic content routing, we would employ consistent hashing to ensure minimal cache revalidation and efficient load balancing across servers. **Cache Invalidation and TTL Strategies:** Effective cache invalidation is critical. We'd support both time-to-live (TTL) based invalidation for predictable updates and explicit invalidation mechanisms (e.g., API-driven purge requests) for real-time content changes. A tiered TTL approach would be adopted: shorter TTLs for frequently updated content and longer TTLs for less dynamic assets, optimizing for both freshness and performance. This would be augmented by Bloom filters for efficient checking of purged objects across the network. **Dynamic Content Acceleration and Edge Compute:** For dynamic content, we'd employ techniques like TLS 1.3 optimization, HTTP/2 multiplexing, and connection pooling at the edge. Furthermore, edge compute capabilities would be integrated, allowing for serverless functions or microservices to execute logic closer to the user, reducing the need to forward every request to origin servers and enabling personalized content delivery and real-time API interactions. **SSL Termination and DDoS Protection:** SSL termination would be handled at the Edge PoPs, decrypting traffic and re-encrypting it to the origin if necessary, reducing the load on origin servers and enabling features like HTTP/2. For DDoS protection, we'd implement a multi-pronged strategy: rate limiting at the edge, IP reputation filtering, signature-based detection of known attack patterns, and anomaly detection to identify and block volumetric and application-layer attacks before they reach the origin. This would be integrated with a global threat intelligence feed. Continuous monitoring of cache hit ratios, latency, and security events is paramount. Proactive analysis of traffic patterns and potential threats allows for preemptive adjustments to caching policies and security configurations, ensuring a resilient and high-performing content delivery network.

Design a Content Delivery Network (CDN)

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