System designHardsd-g598

Subject Cdn cache hierarchyLevel Senior–Staff~45 minCommon in Storage & CDN interviewsIndustries Technology, Telecom

Question

Design a global CDN with a multi-tier cache hierarchy serving static assets and video segments to hundreds of millions of users. Constraints: hundreds of edge PoPs, a target origin offload above 95%, p95 edge cache-hit latency under 30 ms, mixed object sizes (small CSS/JS up to multi-MB video chunks), and the ability to purge a customer's asset globally within seconds. Cover the cache tiers, fill path, and invalidation.

What a strong answer looks like

Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts — data model, bottlenecks, consistency, failure modes — and name the trade-offs you are making.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.