Global CDN cache hierarchy
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.
Clarify5:00 left
Estimate5:00 planned
Design15:00 planned
Deep dive12:00 planned
Failure8:00 planned
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.