Interview Question
A production API's latency doubled overnight. What do you investigate first?
What the interviewer is testing
- Incident framing
- Hypothesis-driven investigation
- Safe mitigation
Real-World Sample Answer
I would approach “A production API's latency doubled overnight. What do you investigate first?” by clarifying the requirements first, then using these considerations: in a real interview, i would not jump straight to a technology choice. for “a production api's latency doubled overnight. what do you investigate first?”, i would first establish the exact time window and affected traffic. then i would compare application, infrastructure, database, and dependency signals and check deployments and traffic changes. i would also use logs, metrics, and traces to narrow the cause. finally, i would separate immediate mitigation from root-cause prevention. 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 “A production API's latency doubled overnight. What do you investigate first?”, I would first establish the exact time window and affected traffic. Then I would compare application, infrastructure, database, and dependency signals and check deployments and traffic changes. I would also use logs, metrics, and traces to narrow the cause. Finally, I would separate immediate mitigation from root-cause prevention. I would make the assumptions explicit and explain what evidence or production signals would make me revisit the decision.
Common Mistakes
- Restarting services without evidence
- Looking at only one metric
- Stopping after mitigation
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?