Problems / Design a product, hard
Design YouTube from an empty canvas: upload and transcode videos, watch them through a CDN, search them and count views, at 2,000 requests a second.
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Request types to route: watch (62%, read), view (25%, write), search (10%, read), upload (3%, write). Budget: $13,000 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 ≤ 300 ms (watch); p99 latency ≤ 400 ms (search); Success ≥ 99.9% (upload) |
| A video goes viral | At 5 s a video goes viral: all traffic triples for 8 s, uploads included. | Success ≥ 99%; p99 latency ≤ 600 ms (watch); Success ≥ 99% (upload) |
| Cache flushed | At 5 s the cache on the request path is emptied, as after a restart or a bad deploy. | Success ≥ 99%; p99 latency ≤ 600 ms (watch) |
| A server dies | At 4 s one server of the first app service on the request path dies for 10 s. | Success ≥ 99% |
| DDoS attack | At 5 s 20,000 requests a second of flood traffic arrive for 10 s, alongside real users. | Attack blocked ≥ 95%; Success ≥ 99%; p99 latency ≤ 400 ms (watch) |
| Budget: $13,000/month | The normal day's design must cost at most $13,000 a month. | Cost ≤ $13,000/month |