Problems / Design a product, medium
Design a notification system from an empty canvas: accept requests from other services, queue them, and have workers deliver push, email and SMS through the providers, with dedupe and per-user rate limits.
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Request types to route: send (80%, write), status (20%, read). Budget: $50,000 a month.
You start from an empty canvas. When you run the tests, each one simulates your design with its own traffic and failures:
| Test | What it does | Passes when |
|---|---|---|
| Normal day | The normal day: the traffic in the brief, nothing broken. | Success ≥ 99.9%; p99 latency ≤ 100 ms (send) |
| A marketing campaign | At 5 s a campaign goes out: requests quadruple for 8 s. | Success ≥ 99%; p99 latency ≤ 300 ms (send) |
| A provider slows down | At 5 s the push, email and SMS provider answers 10× slower for 8 s. While this test runs, brokers redeliver unacknowledged messages after 5 s and 0.2% of acknowledgements are lost, as in production: only idempotent consumers avoid duplicates. | Success ≥ 99%; p99 latency ≤ 300 ms (send); No duplicate side effects |
| Budget: $50,000/month | The normal day's design must cost at most $50,000 a month. | Cost ≤ $50,000/month |