System designMediumsd-g005

Subject Notification systemsLevel Mid–Senior~40 minCommon in Networking & APIs interviewsIndustries Technology, Software development

Question

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.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.