Cianplan

Level 6: Applied: cases, FDE scenarios, mocks · L6.2 Classic cases II

Chat app

Design WebSocket fan-out, message ordering and offline delivery.

15 min · Pro

What you take away

  • Twenty million concurrent connections at about 100k per server is roughly 200 stateful gateways, and the registry mapping user to gateway is on the hot path for every message.

And 3 more inside the class, in Pro.

How the class is laid out

  1. The prompt
  2. Requirements and the numbers
  3. The design
  4. Three decisions
  5. The twist
  6. Check your understanding