On-callHardoc-g524

Subject Scaling limitsLevel Senior–Staff~30 minCommon in Networking & APIs interviewsIndustries Technology

Question

Your fleet makes lots of short-lived outbound HTTPS calls to several third-party APIs and egresses through a managed NAT gateway. You scaled the fleet from 60 to 150 instances for a campaign; outbound success rate dropped and you see intermittent connection timeouts and resets to external endpoints. The third-party APIs are healthy and not rate-limiting you. NAT gateway metrics show `ErrorPortAllocation` climbing and active connection count near a ceiling. How do you triage and what's the durable fix?

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.