System designHardsd-g513

Subject Notification systemsLevel Senior–Staff~50 minCommon in Networking & APIs · Distributed systems interviewsIndustries Technology, Software development

Question

Design a webhook fan-out system with per-subscriber backpressure. Your platform emits events (e.g. payment.succeeded) and customers register HTTPS endpoints to receive them. Scale: 1M events/sec across 100K subscriber endpoints; some endpoints are fast (10ms), some are slow (5s) or down for hours. One slow/dead subscriber must not delay delivery to healthy ones, and you must retry with backoff, preserve per-subscriber ordering where promised, and guarantee at-least-once delivery.

What a strong answer looks like

Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts — data model, bottlenecks, consistency, failure modes — and name the trade-offs you are making.

Learn the concepts

Narrate your design

Loading whiteboard…

Run or narrate your approach, then ask the coach.