Problems / Design a product, hard
Design Zoom from an empty canvas: signalling over a WebSocket gateway, audio and video through media servers (SFUs), meeting state in a store, and calls that survive losing a media server.
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Request types to route: media (85%, write), signal (10%, write), join (5%, write). Budget: $4,500 a month.
You start from an empty canvas. When you run the tests, each one simulates your design with its own traffic and failures:
| Test | What it does | Passes when |
|---|---|---|
| Normal day | The normal day: the traffic in the brief, nothing broken. | Success ≥ 99.8%; p99 latency ≤ 150 ms (media); p99 latency ≤ 500 ms (join) |
| Top of the hour | At 5 s the hour turns: everyone joins their next meeting and traffic doubles for 8 s. | Success ≥ 99%; p99 latency ≤ 250 ms (media) |
| A media server dies | At 5 s one media server (SFU) crashes and takes 10 s to restart; the calls on it must carry on on the others. | Success ≥ 99%; Success ≥ 99% (media); p99 latency ≤ 250 ms (media) |
| DDoS attack | At 5 s 20,000 requests a second of flood traffic arrive for 10 s, alongside real users. | Success ≥ 99%; Attack blocked ≥ 95% |
| Budget: $4,500/month | The normal day's design must cost at most $4,500 a month. | Cost ≤ $4,500/month |