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Clarify requirements before you design — kept separate from your stage notes.

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CDN System Design

Visual Problem Diagram

Scenario

A trailer drop spikes 8 Tbps at the edge; origin would melt without cache hit ratio > 95% and shield POPs. One bad Cache-Control header caches a personalized API response for every user in Europe—the interview is caching semantics, invalidation, and origin protection, not listing CDN vendor names.

Design a content delivery network that caches static and streaming content at edge locations close to users. Success is hit ratio, origin protection, and correct cache semantics—not POP count alone.

You should support edge caching, DNS-based routing, origin pull, invalidation, and HTTPS. Be ready to explain cache keys, TTL strategy, shield tiers, and video segment caching.

Constraints

Functional

Edge cache static/video, DNS geo routing, origin pull, purge/invalidation, HTTPS at edge

Non-functional

> 95% cache hit for static, < 50 ms edge latency p95, protect origin from stampede, global availability

Scale

Tbps peak egress, millions of assets, billions of requests/day, thousands of POPs

Stages ahead

1Requirement Analysis

2API Design

3High-Level Design

4HLD Extensions

5Trade-offs

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