Cold cache stampede after restart
Your read path is fronted by a large Redis cluster that normally absorbs 98% of traffic. After a planned cluster-wide Redis restart for a version upgrade at 02:00, the cache comes back completely empty. The instant the app fleet starts serving again, origin DB CPU pins at 100%, p99 jumps 40x, and the DB shows thousands of identical queries per popular key — the warm-up never converges and the DB stays saturated for 20+ minutes. CPU on the app tier is fine. How do you triage and mitigate the cold-cache stampede?
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 30 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.