Design a notification service that, based on events from other services, sends users email, push notifications and SMS, at up to several million notifications a day.
~10 min by voice
How to approach it
This checks whether the candidate can build an asynchronous message delivery pipeline: a broker instead of synchronous calls, independent channels, reliability (retries, DLQ, idempotency) and the real constraints of external providers. Interviewers also watch whether they remember the user: preferences, priorities, no duplicates.
The interviewer will ask this question and listen. Think out loud and ask for a hint if you need one. When you're done, pause or tap “That's my answer”. In about a minute, your score and the points you covered show up here.