Hard · 11 steps · ~75 min

Design a collaborative editor

Many people typing in one document, and nobody's edit lost.

Edits from many people must reach everyone quickly and merge without losing anyone's work. Every keystroke is a tiny write.

Same problem as Google DocsNotionFigma

How it works

• Type: each edit is sent over an open connection.
• Merge: edits are ordered in a log and applied to the document.

What you'll build

1. The API and the data behind it
2. Realtime gateways for open connections
3. A log (stream) of edits with workers that apply them
4. Shards for write-heavy scale
5. A design that survives a cold cache and a lost gateway

Steps

1. 1Design the API
2. 2Design the data model
3. 3Handle 1,000 requests/sec
4. 4Handle 15,000 requests/sec for $1,500 a month
5. 5Handle 40,000 requests/sec
6. 6Handle 80,000 requests/sec
7. 7Survive a bot flooding the editor
8. 8Survive a cache restart
9. 9Lose a realtime gateway
10. 10Two people edit the same word
11. 11Deep dive: opening a long document