System design interview question
Design a Global Content Delivery and Cache Invalidation System for a CDN (Like Cloudflare at Scale)
Design a distributed content delivery network that serves static and semi-static content to 500M monthly users across 6 continents, with 50K edge locations and 1M requests per second peak traffic. The system must support instant cache invalidation across all edge nodes within 500ms, handle geographic routing with latency optimization, manage distributed consensus for cache state, and provide real-time analytics on cache hit rates, origin load, and user experience metrics. Key constraints include: sub-100ms p99 latency for cache lookups, support for both purge-by-URL and purge-by-tag operations, handling of origin shield patterns, and graceful degradation during network partitions. Candidates should design the control plane, data plane, cache coherency protocol, and operational observability required to serve this scale reliably.
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