Architecture & Pipeline Design:
- Goal: Deliver millions of daily notifications across multi-channel providers with retry resilience, prioritization, and user preference controls.
1. Ingestion & API Layer:
- API Gateway accepts notification requests: { user_id, event_type, priority, template_id, variables }.
- Validates payload, verifies idempotency keys to prevent duplicate dispatches, and returns 202 Accepted immediately.
2. Priority Queues & Partitioning:
- Ingest events into partitioned message queues (Kafka / RabbitMQ) segregated by priority:
- Critical Queue: Auth OTPs, fraud alerts (processed immediately with dedicated worker pool).
- Bulk Queue: Marketing newsletters, weekly summaries (rate-limited).
3. Preference & Formatting Engine:
- User Preferences Service: Evaluates user channel opt-ins, quiet hours, and frequency caps stored in Redis/DynamoDB.
- Template Renderer: Hydrates dynamic user variables into localized HTML/plain-text templates.
4. Third-Party Provider Dispatch & Resilience:
- Dedicated worker pools for each provider (SES/SendGrid for email, Twilio for SMS, APNs/FCM for push).
- Dead Letter Queue (DLQ): Failed dispatches with transient errors retry with exponential backoff and jitter. Hard failures route to DLQ for operational alerts.