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Design a Multi-Channel Notification System

Build a scalable notification platform that delivers billions of messages across multiple channels while respecting user preferences and ensuring reliable delivery.

Q: What's the expected notification volume?
A: 100 million notifications daily, with peak traffic of 50K notifications per second during events and campaigns.
💡 This scale requires distributed queue systems and auto-scaling workers. Peak-to-average ratio of 3-4x suggests we need capacity planning for surge handling.
Q: Which notification channels should we support?
A: Email, SMS, push notifications (iOS/Android), in-app notifications, and web push. Future support for WhatsApp and Slack integrations.
💡 Multi-channel support requires channel adapters and provider abstraction. Each channel has different latency, cost, and reliability characteristics.
Q: What are the delivery guarantees and SLA requirements?
A: 99.9% delivery success rate overall. Critical notifications (security, transactions) need <1 second delivery. Marketing messages can tolerate 5-10 minute delays.
💡 Need priority queues with different SLA tiers. Critical notifications should bypass rate limits and have dedicated processing capacity.
Q: How should we handle user preferences and privacy?
A: Full user control over notification preferences, quiet hours, frequency caps, and channel selection. GDPR/CCPA compliance required.
💡 Preference service needs real-time updates and audit trails. Opt-outs must be honored immediately, even for queued notifications.
Q: What types of notifications will we send?
A: Transactional (order confirmations), security alerts, marketing campaigns, product updates, and real-time notifications (chat, likes).
💡 Different types have varying priority, personalization needs, and regulatory requirements. Template management becomes critical at scale.
Q: Do we need tracking and analytics?
A: Yes, comprehensive tracking: delivery status, open rates, click-through rates, bounce handling, and engagement analytics.
💡 Analytics pipeline needs to handle high-volume events while maintaining user privacy. Real-time dashboards for campaign monitoring.
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Interview Practice Questions

Practice these open-ended questions to prepare for system design interviews. Think through each scenario and discuss trade-offs.

1

Multi-Channel Enterprise Notification Platform: Design a notification system for enterprises supporting email, SMS, push notifications, Slack, Teams, and webhooks. Handle 100M+ daily notifications with user preferences, compliance tracking, and advanced analytics.

2

Real-Time Social Media Notifications: Build a notification system for a social platform handling likes, comments, mentions, friend requests, and live events. Support 500M+ users with instant delivery, smart batching, and engagement optimization.

3

IoT & Smart Device Notifications: Design a notification system for IoT devices, smart homes, and industrial sensors. Handle device states, alert escalation, emergency notifications, and integration with various protocols and platforms.

4

Financial Services Alert System: Build a notification system for banking and financial services with transaction alerts, fraud detection, market updates, and regulatory notifications. Address security, compliance, and real-time requirements.

5

Healthcare Critical Alert System: Design a notification system for healthcare providers with patient monitoring, emergency alerts, medication reminders, and clinical workflow notifications. Handle life-critical scenarios and regulatory compliance.

6

E-commerce Marketing Automation: Build a notification system for e-commerce with personalized marketing campaigns, abandoned cart recovery, inventory alerts, and order updates. Support behavioral triggers, A/B testing, and revenue optimization.