Netflix global recommendation system design challenge under licensing constraints

Definition

A company rejected me, but I still love this system design question: Design Netflix’s global content recommendation system where every row must respect country licensing, in under 50ms p99. Constraints to make it real: 1) User opens Home: return 200 items across 20 rails (Because you watched, Trending, Continue Watching, etc.) 2) Licensing rules change hourly: country, region, time window, device type, kids profile, downloads 3) Per-request context: geo from IP, account country, travel mode, VPN suspicion, language, maturity level 4) Must hard-filter unlicensed titles, not just down-rank them 5) Personalization model updates continuously, but serving must stay <50ms p99 at peak (millions QPS) 6) Global: multi-region active-active, no cross-region synchronous calls in the hot path 7) Cold start: new users + new titles + new countries launching this week 8) Explainability requirements: show why a row appeared, but without leaking restricted titles 9) Cache strategy: what do you cache, at what key granularity, and how do you invalidate on license flips 10) Failure modes: licensing service down, model store stale, partial region outage. What do you return and how do you stay compliant

Sources

• raw/Tech/2026-06-29-0xlelouch_-netflix-global-recommendation-system-design-challenge-under-licensing.md