Case Study: A Notification System

1. The Question

"Design a notification system for a large platform: any service can request that a user be notified; delivery goes over push, email, and SMS; users control preferences. Around 100 million notifications a day."

This one is not a product. It is plumbing, and every interview loop asks about it.

Every case study so far has been a product people use. This one is an infrastructure component, meaning a shared internal service that other services depend on. Every company builds one of these once.

It is also the purest showcase for the async half of this course