Design a chat messaging system
Company: Meta
Role: Software Engineer
Category: System Design
Difficulty: medium
Interview Round: Onsite
Design a chat system similar to WhatsApp/Messenger.
Requirements:
- 1:1 and group chats.
- Send/receive messages in real time when online; store-and-forward when offline.
- Delivery states (sent/delivered/read) are desirable.
- Support message history sync across devices.
- Handle ordering within a conversation.
Out of scope: end-to-end encryption details, media pipeline.
Overview: This question evaluates the ability to design scalable, reliable real-time messaging systems, examining competencies in distributed systems, message delivery semantics (sent/delivered/read), offline store-and-forward, multi-device history synchronization, and conversation ordering.