This document outlines the architecture for a centralized notification service designed to deliver Push, SMS, and Email notifications to an active user base of 1M+ users. The system is engineered for high reliability, guaranteeing zero missed sends, exactly-once processing (idempotency), and graceful degradation in the event of third-party provider outages.
- Expose an internal API for microservices to enqueue notifications.
- Support multiple delivery channels: Email (e.g., SendGrid), SMS (e.g., Twilio), and Push (e.g., FCM/APNs).