Design
Distributed Notification Fanout System
Design a system that reliably delivers notifications (push, SMS, email) to millions of users with dedup, retries, and prioritization.
01 - Why interviewers ask this
It tests queue-based fan-out design under massive scale — interviewers check for deduplication and priority handling, not just "loop over all users and send".
02 - Where this system exists in the real world
You interact with this design every day.
AWS SNS / Firebase Cloud Messaging infrastructure
Mass marketing/broadcast notification systems
Critical alerting systems (incident/security)
03 - What you'll master
Solve this once. Know it forever.
Design a queue-based fan-out pipeline
Deduplicate notifications reliably
Prioritize critical vs. bulk notification traffic
04 - What you'll design
6 functional · 3 non-functional requirements.
Accept a notification request targeting a user, group, or topic subscribers
5 more requirements inside
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05 - Companies that ask this
You may face this exact question in your next interview.
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