System Design Deep Dive: CDN Caching Proxy

This section provides comprehensive system design analyses across all 17 core distributed systems dimensions.

Topic #	Chapter Title	Core Architectural Focus
14.1	Requirements & Capacity Estimation	Capacity arithmetic, RPS sizing, bandwidth offload calculations.
14.2	Architecture Styles	Reverse proxy edge architecture and layered stream processing.
14.3	Networking & Communication	Keep-alive socket pools, TLS termination, and stream backpressure.
14.4	Load Balancing & Scaling	Ketama consistent hash rings, origin pool weights, and failover.
14.5	Databases & Storage Architecture	In-memory segment allocator backed by disk stores with compaction.
14.6	Deep Caching Architecture	RFC 9111 rules, single-flight request coalescing, and stale serving.
14.7	Messaging & Queues	Asynchronous purge worker queue and dead-letter retries.
14.8	Consistency & Concurrency	Cache coherency, tag purge atomicity, and Vary variant isolation.
14.9	Reliability & Resilience	Circuit breakers, active synthetic probes, and stale-if-error fallback.
14.10	API Design & Rate Limiting	Admin REST API, Bearer token auth, CORS, and tenant quotas.
14.11	Security Architecture	Edge WAF, CIDR IP filtering, Host verification, and SSRF defense.
14.12	Search & AI Architecture	Inverted tag index and Tier A/B predictive prefetch AI models.
14.13	Real-Time Systems & Telemetry	1-second polling time-series metrics and live decision ring buffer.
14.14	Observability & Operations	Prometheus metrics, W3C traceparent propagation, and structured logs.
14.15	Performance Engineering	Zero-copy stream piping, forced GC memory checks, and CPU profiling.
14.16	Cost & Architectural Trade-Offs	Egress cloud bandwidth savings vs edge memory hosting expenses.
14.17	Classic System Design Questions	Scaling to 100x, media streaming, notifications, and rate limiters.
ADR	Architecture Decision Records (ADR)	Master log of all architectural decisions and accepted trade-offs.