System design interview question
Design a Multi-Region Real-Time Notification Delivery System for 500M Users
Design a notification delivery platform that handles 50K notifications/second globally across 6 regions, with sub-second delivery guarantees for critical alerts and best-effort for marketing messages. Users must receive notifications on multiple channels (push, email, SMS, in-app) with deduplication, rate limiting, and delivery guarantees. The system must support user preference management, A/B testing of message variants, and provide real-time analytics on delivery success rates, open rates, and engagement metrics. Consider handling intermittent connection issues, ensuring exactly-once delivery semantics for financial alerts, and maintaining global consistency of user preferences while optimizing for regional latency.
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