Multi-channel notification platform
Design a multi-channel notification platform (push, email, SMS, in-app) for a 100M-user product where dozens of internal services emit notification-worthy events. Requirements: never send the same logical notification twice, honor per-user channel preferences and quiet hours/timezones, cap each user at a sane volume so we don't spam them, and degrade gracefully when a downstream provider (e.g. APNs or an SMS gateway) is throttling. Walk through the pipeline.
What a strong answer looks like
Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts (data model, bottlenecks, consistency, failure modes) and name the trade-offs you are making.
Clarify4:30 left
Estimate4:30 planned
Design13:30 planned
Deep dive10:30 planned
Failure7:00 planned
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.