On-callMediumoc-g039

Subject Head of line blockingLevel Mid–Senior~30 minCommon in Networking & APIs · Algorithms & data structures interviewsIndustries Technology, Software development

Question

An API gateway (single shared worker pool / request queue) fronts both fast lightweight reads (~5ms) and a handful of expensive report-export endpoints (~8s each). At 15:00 a customer scripts a burst of report-export calls. Suddenly *all* traffic through the gateway, including the 5ms health checks and reads, sees latency jump to multiple seconds and some time out. Export volume is small in count but each is long-running. Triage and explain the blocking mechanism, then mitigate.

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.