Design 2: Designing a Scalable Notification System
Let’s walk through the design of a scalable multi-channel notification system that can deliver messages via Email, SMS, and Push channels in real-time.
Step 1: Define Functional Requirements
- Send notifications via Email, SMS, and Push
- Support user preferences and notification types
- Asynchronous processing and retry logic
- Template-based notifications with dynamic data
- APIs for triggering notifications programmatically
Step 2: Define Non-Functional Requirements
- High availability and fault tolerance
- Scalability to millions of messages per day
- Latency: Near real-time delivery
- Extensibility: Easy to add new channels
- Monitoring, logging, and retry management
Step 3: Define API Services
- POST /send-notification
- GET /user-preferences
- PUT /user-preferences
- POST /template
- GET /delivery-status
Step 4: High-Level Architecture
- API Gateway: Receives notification requests
- Producer Service: Publishes events to message queue (Kafka/SQS)
- Queue: Decouples producers and consumers
- Worker Service: Consumes events and sends to respective channel (Email/SMS/Push)
- Template Service: Renders dynamic templates with data
- Channel Adapter: Integrates with providers like SendGrid, Twilio, FCM
- Audit/Status Store: Stores delivery logs and status
Step 5: Key Architectural Decisions
- Use message queues for async and retry support
- Keep channel adapters pluggable and fault-isolated
- Enable idempotency to avoid duplicate sends
- Support exponential backoff for retries
- Separate metadata and payload for flexibility
Step 6: Additional Considerations
- User-level rate limiting and suppression
- Opt-in/opt-out and Do Not Disturb windows
- Observability: Dashboards for delivery rates and failures
- Compliance: GDPR, CAN-SPAM, etc.
- Redundancy: Backup providers for failover
Conclusion
Designing a scalable notification system requires asynchronous processing, extensible architecture, delivery guarantees, and strong user preference handling. Choosing the right abstractions can help build a reliable and maintainable system that handles millions of notifications across different channels.