System designEasysd-g552

Subject Rate limitingLevel Entry–Mid~25 minCommon in Networking & APIs interviewsIndustries Software development, Technology

Question

Design a basic rate limiter for a single public API endpoint so no client can call it more than 100 times per minute. Clients are identified by API key. The API runs on a couple of server instances behind a load balancer. Describe how you count requests and decide when to reject (return 429).

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.