On-callMediumoc-p101

Subject CapacityLevel Senior~20 minCommon in Reliability & on-call interviewsIndustries Technology, Software development

Question

After scaling a service from 10 to 50 instances to handle growth, the database started rejecting connections ('too many connections') even though per-instance load went down. What happened?

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.