On-callHardoc-g303

Subject Dependency outagesLevel Senior–Staff~40 minCommon in Reliability & on-call · Code quality & review interviewsIndustries Technology

Question

Your read path is cache (Redis) in front of a database, ~95% hit rate normally. At 21:00 the managed Redis has a brief blip — it's only unreachable for 8 seconds — but it comes back EMPTY (the failover cleared it). For the next several minutes your database is melting: DB CPU 100%, connection pool exhausted, query latency 10x, app error rate 35%. Redis itself is now healthy and reachable; it's just cold. No deploy. The 8-second blip ended minutes ago. How do you triage and mitigate?

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.