On-callMediumoc-g055

Subject Feature flagLevel Mid–Senior~30 minCommon in Databases & SQL interviewsIndustries Technology, Software development

Question

An incident is in progress: a buggy 'new_comment_ranking' code path is throwing for 4% of comment loads. You flip its kill-switch flag to OFF at 21:10. The error rate drops for some pods but ~30% of pods keep throwing the same error for another 8 minutes, then they too recover with no further action. The flag SDK caches flag values locally and polls the flag service every 5 minutes; the flag service confirms OFF immediately. Triage and explain what happened and how to prevent it.

What a strong answer looks like

Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.

Learn the concepts

Diagram & narrate the incident

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Run or narrate your approach, then ask the coach.