Cache stampede after Redis failover
Your product catalog service (Go, Redis cache in front of Postgres) serves 40k rps at peak. At 09:02 a Redis cluster failover completes after a node crash; the new primary comes up with an empty keyspace. Immediately, p99 on GET /product/{id} spikes from 25ms to 9s, Postgres CPU pegs at 100%, the Go service's goroutine count balloons from ~2k to 200k, and you start seeing context-deadline-exceeded errors. Redis hit rate is near 0% and slowly recovering. No code deploy occurred. 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.
0:00 of about 40 min
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.