Event loop synchronous crypto
A Node.js notification service starts timing out health checks and dropping WebSocket connections under moderate load. Dashboards: event-loop lag (measured via `perf_hooks`) spikes from <5ms to 400ms+ and stays there; CPU on the single Node process is pinned at 100% on one core while the box has 7 idle cores; the async task queue (in-process) grows without bound. A feature shipped yesterday generates a personalized digest by doing synchronous JSON parsing + template rendering + a `bcrypt`-style hashing step inline in the request handler. Triage and remediate.
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.