On-callMediumoc-g540

Subject Health flappingLevel Entry–Mid~20 minCommon in Networking & APIs interviewsIndustries Technology, Software development

Question

After a deploy, a service's instances keep flapping in and out of the load balancer's healthy pool — the dashboard shows hosts being marked unhealthy, removed, then re-added a minute later, over and over. User-facing error rates are spiky as capacity bounces. The new build added a deeper health check that also pings a downstream dependency. How do you triage the flapping?

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.