Interview Simulator · System Design
Design a Notification System
A full 45 minute round, one phase at a time. Each phase has a time budget, follow-up questions from the interviewer, and a checklist for your level. Reveal a phase's model answer whenever you need it; the report shows which phases you earned.
Design a notification system that sends push, email, and SMS on behalf of other services. It serves 200 million users who each get about 10 notifications a day. It respects each user's preferences, never sends the same notification twice, and retries when a provider fails.