Practice series
Realtime chat, sync & collaboration
Messaging, WebSockets, local-first state, CRDT/OT, fan-out, and backfill.
- 01Preview
Chat App
Design the client-side architecture of a WhatsApp-style mobile messenger — connection handling, message state, offline storage, and encryption all have to survi...
Discord - 02Preview
Chat Service
Design the backend infrastructure behind a chat product — stateful connection servers, message storage, and group fan-out — for hundreds of millions of concurre...
Discord - 03Preview
Collaborative Shopping
Design a collaborative shopping experience where multiple people share a single cart in real time, add and remove items concurrently, and one designated partici...
Practice bank - 04Free
Dropbox
Design Dropbox — a cloud file storage and synchronization service where users upload large files and keep them in sync across devices and shared folders.
Dropbox - 05Free
Facebook Messenger
Design Facebook Messenger — a real-time chat system delivering messages with low latency, ordering guarantees, and multi-device sync at massive scale.
Meta - 06Preview
Google Doc
Design Google Docs’ real-time collaborative editing — multiple users typing in the same document simultaneously and seeing each other’s edits converge correctly...
Google - 07Preview
Google Drive
Design Google Drive as a permissioned file platform — folder hierarchies, shared drives, and access control that scale across billions of files and third-party...
Google - 08Preview
Real-time Multiplayer Game
Design an authoritative server for a real-time multiplayer game.
Riot Games - 09Preview
Live Comments
Design a live comments system that fans out comments from one live event to millions of concurrent viewers in real time.
Meta