How would you protect an API from a sudden 20× traffic spike while keeping legitimate users served?

Interview Question

What the interviewer is testing

Capacity planning
Fairness
Graceful degradation

Real-World Sample Answer

I would approach “How would you protect an API from a sudden 20× traffic spike while keeping legitimate users served?” by clarifying the requirements first, then using these considerations: in a real interview, i would not jump straight to a technology choice. for “how would you protect an api from a sudden 20× traffic spike while keeping legitimate users served?”, i would first identify the actual bottleneck and capacity envelope. then i would use rate limiting or quotas to protect dependencies and scale stateless layers where useful. i would also cache or shed non-critical work. finally, i would monitor saturation and recovery. i would make the assumptions explicit and explain what evidence or production signals would make me revisit the decision.. I would state my assumptions and defend the trade-offs rather than presenting the choice as universally correct.

What a Strong Answer Should Cover

In a real interview, I would not jump straight to a technology choice. For “How would you protect an API from a sudden 20× traffic spike while keeping legitimate users served?”, I would first identify the actual bottleneck and capacity envelope. Then I would use rate limiting or quotas to protect dependencies and scale stateless layers where useful. I would also cache or shed non-critical work. Finally, I would monitor saturation and recovery. I would make the assumptions explicit and explain what evidence or production signals would make me revisit the decision.

Common Mistakes

Autoscaling everything
No protection for downstream dependencies
No graceful degradation plan

Interviewer Follow-ups

What assumptions would you clarify before committing to the design?
What changes if the scale, reliability target, security requirement, or budget changes?
What is the biggest failure mode in your proposed approach?

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