System designMediumsd-g524

Subject Notification systemsLevel Mid–Senior~40 minCommon in Distributed systems interviewsIndustries Technology, Software development

Question

Design a multi-channel notification orchestration service. Internal services emit 'notify user U about event E'; the service decides channel (push, SMS, email, in-app), respects per-user preferences and quiet hours, deduplicates so a user isn't pinged 5 times for the same logical event from 5 services, batches digestible low-priority notifications, and honors rate limits/opt-outs. Scale: 50M users, 200K notify requests/sec at peak.

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.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.