System designHardsd-g048

Subject Rate limitingLevel Senior–Staff~45 minCommon in Networking & APIs · Distributed systems · Algorithms & data structures interviewsIndustries Technology, Software development

Question

Design a distributed rate limiter for a public API gateway with 200 edge nodes across regions enforcing per-API-key quotas (e.g., 1000 requests/minute). Limits must be enforced globally (a key can't get 1000/min per node), the limiter must add <1ms p99, and it must fail open if the limit store is unreachable. Walk through the algorithm, where state lives, and the consistency/latency trade-off.

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.