1. Design a notification system that sends email, SMS, and push notifications to millions of users.
Interview promptStrong signal
Looks for queues, rate limits, retries, provider failover, user preferences, idempotency, and observability.
Follow-up probes
- •How do you handle provider outages?
- •How do you prevent duplicate sends?
Red flags
- •Sends synchronously from the API.
- •No backpressure or retry strategy.