Problems / Design a product, hard
Design the Facebook news feed from an empty canvas: retrieve candidates from precomputed feeds, rank them with a model on every load, and take posts and likes, at 3,000 requests a second.
Unlock it once for 25 credits; everything inside it is free (runs, changes, Submit, results, hints). Sign in with Google to start; new accounts get free credits.
Request types to route: feed (75%, read), like (20%, write), post (5%, write). Budget: $7,000 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 ≥ 99.9%; p99 latency ≤ 250 ms (feed); p99 latency ≤ 150 ms (like) |
| Evening peak | At 5 s the evening rush begins: traffic jumps to 2.5× for 8 s. | Success ≥ 99%; p99 latency ≤ 500 ms (feed) |
| 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 (feed) |
| A server dies | At 4 s one server of the first app service on the request path dies for 10 s. | Success ≥ 99% |
| Budget: $7,000/month | The normal day's design must cost at most $7,000 a month. | Cost ≤ $7,000/month |