On-callHardoc-g090

Subject Autoscaling failureLevel Senior–Staff~40 minCommon in Reliability & on-call interviewsIndustries Technology

Question

Your checkout service runs on Kubernetes with an HPA targeting 60% CPU. During a flash sale, latency climbs and pods start OOMKilling, but the HPA holds the deployment at its current 12 replicas and never scales up. `kubectl describe hpa` shows `unknown / 60%` for the CPU metric and an event `failed to get cpu utilization: unable to fetch metrics from resource metrics API`. The metrics-server pod restarted 6 minutes ago. The deployment has `maxReplicas: 80` and the cluster has spare nodes. How do you triage and get checkout scaling again?

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.