Problems / Design a product, hard
Design Instagram from an empty canvas: post photos, resize them in the background, fan posts out into precomputed timelines, serve feeds and photos, and count likes, at 2,500 requests a second.
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Request types to route: feed (50%, read), media (30%, read), like (15%, write), post (5%, write). Budget: $11,000 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 ≤ 300 ms (feed); p99 latency ≤ 300 ms (media); Success ≥ 99.9% (post) |
| A celebrity posts | At 5 s a celebrity posts: traffic triples for 8 s as millions open the app and like it. | Success ≥ 99%; p99 latency ≤ 500 ms (feed); Success ≥ 99% (like) |
| The timeline cache flushed | At 5 s the timeline cache is emptied, as after a restart or a bad deploy: every read misses until it warms up again. | Success ≥ 99%; p99 latency ≤ 500 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: $11,000/month | The normal day's design must cost at most $11,000 a month. | Cost ≤ $11,000/month |