On-callMediumoc-g095

Subject Cold startLevel Mid–Senior~30 minCommon in Concurrency interviewsIndustries Technology

Question

Your API is a Lambda behind API Gateway. After a quiet overnight period, the 08:00 traffic ramp causes p99 to spike to 4–8s for the first few minutes while p50 stays at 120ms. CloudWatch shows `Init Duration` appearing on a large fraction of invocations during the ramp, `ConcurrentExecutions` climbing fast, and a few `Throttles`. The function loads a large ML model and opens a DB connection in its init code. No deploy happened. How do you triage and reduce the morning latency cliff?

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

Loading whiteboard…

Run or narrate your approach, then ask the coach.