On-callHardoc-g522

Subject Traffic surgeLevel Senior–Staff~30 minCommon in Distributed systems · Code quality & review interviewsIndustries Technology

Question

A big live event drives a 6x surge to your video-start API. That service autoscales fine and stays healthy, but starts failing because a shared `entitlement` service it calls (also used by 9 other teams) saturates: the entitlement service's DB connection pool is exhausted and it returns 503s, which cascade into your video-starts AND degrade the 9 unrelated teams. Your service is already correctly caching entitlements for 60s. How do you triage and mitigate, balancing your incident against the shared-dependency blast radius?

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.