End-to-end encrypted real-time messaging with presence tracking, message queuing for offline users, and media delivery.
Difficulty: advanced
Tags: messaging, real-time, websockets, e2e-encryption
WhatsApp delivers billions of messages daily to 2B+ users with end-to-end encryption and sub-second delivery. The architecture centers on persistent WebSocket connections managed by a connection service, with an intelligent message router that handles online delivery instantly and queues messages for offline recipients. Designed for teams building encrypted messaging platforms that prioritize delivery reliability and end-to-end privacy at scale.