Instant traffic wall
Tickets for a major concert go on sale at exactly 10:00. At 10:00:00 traffic jumps 50x instantly. Your ALB starts returning 503s, the autoscaler is adding instances but they take ~4 minutes to boot and pass health checks, and during those 4 minutes the small initial fleet is overwhelmed and crashes. The queue page itself is dynamic and hits the same backend as checkout. Nothing is broken in code; you simply got a wall of traffic at a known instant. How do you triage in the moment and design for the next on-sale?
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 35 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.