Thread pool starvation
A Python web app (gunicorn with sync workers, 4 workers × 8 threads = 32 concurrent slots) fronts three downstream services: auth, billing, and recommendations. At 18:00 the recommendations service (a non-critical sidebar widget) starts taking 10s per call instead of 50ms. Within minutes your *entire* app — including login and checkout, which don't even touch recommendations — becomes unresponsive and starts timing out. Recommendations is only ~5% of your traffic. Triage and explain why a slow non-critical dependency took down everything.
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.