System Design: Messenger service like Whatsapp or WeChat - Interview Question

Here is the link.

1. One one text
2. Sent/ Delivered/ Read
3. Push notifications

Offline, the messages are sent in wrong order.

Second feature:

Dive deep:

Multicast messaging, like cache, database replication, sharding, store of message, usage limit, premium service, load balancing,

Features -> Architecture

Simple feature first, and then grow architecture, the interviewer will tell you what he likes you to talk about.