On-callMediumoc-g008

Subject Database incidentsLevel Mid–Senior~30 minCommon in Databases & SQL · Reliability & on-call interviewsIndustries Technology, Software development

Question

Your product runs as AWS Lambda functions (Node.js) talking directly to an RDS Postgres instance (max_connections=200). A marketing email went out at noon and traffic spiked 8x. The API starts returning 500s with 'remaining connection slots are reserved' / 'too many clients already'. CloudWatch shows Lambda concurrency briefly hit 600. The DB CPU is only at 40%. How do you triage and mitigate, and what's the right architecture?

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.