Webhook delivery with backpressure
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.
Clarify5:30 left
Estimate5:30 planned
Design16:30 planned
Deep dive13:30 planned
Failure9:00 planned
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.