System designHardsd-g317

Subject Traffic shapingLevel Senior–Staff~45 minCommon in Distributed systems interviewsIndustries Technology

Question

A payments API is approaching overload during a flash sale: incoming traffic exceeds capacity and naive behavior (accept everything) is driving latency up and triggering client retries that make it worse (a retry storm / metastable failure). Design adaptive traffic shaping and load shedding that keeps the system in a healthy regime. Cover how you decide what to shed vs admit, how you prioritize (a checkout vs a balance-poll), how you prevent retries from amplifying overload, and how the system recovers once it's tipped over.

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.