Explain Push Notifications Architecture.
Push notifications architecture is the system that queues, personalizes, and delivers real-time messages from your backend to user devices through APNs (Apple) or FCM (Google), with retries, feedback, and analytics.
When to Use
- Transactional: OTPs, receipts.
- Real-time updates: delivery tracking, sports scores.
- Ops/security: outage alerts, suspicious logins.
- Marketing: discounts, reminders (opt-in only).
Example
An e-commerce backend publishes order_shipped; the notification service looks up the device token, picks a template, and forwards it to FCM/APNs. Failures retry with backoff and a dead-letter queue.
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Why Is It Important
Push architecture decouples producers from delivery, scales to millions, supports retries, ensures idempotency, and adds observability (delivery/engagement metrics).
Interview Tips
Sketch the flow: producers → queue → workers → APNs/FCM → device. Discuss:
- QoS (TTL, collapse keys, rate limits).
- Resilience (token rotation, retries, DLQ).
- SLOs (latency, success rate).
Trade-offs
- Latency vs durability (immediate vs queued).
- Personalization vs privacy (data storage trade-offs).
- Throughput vs cost (multi-region infra).
- Battery life vs freshness (batching vs instant).
Pitfalls
- Over-notifying users.
- Ignoring opt-in/quiet hours.
- Not handling token churn.
- Assuming delivery = read (measure opens instead).
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