Design a group chat system

Q: Design a group chat system

This question evaluates competency in designing real-time distributed messaging systems, covering scalability, data modeling, API design, consistency models, ordering and fan-out strategies, fault tolerance, and operational monitoring.

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Question

Design a WhatsApp-like group chat system.

Core features:

1:1 and group conversations
Send/receive text messages (assume small payloads)
Group membership management (add/remove users)
Message history sync across devices

Non-functional requirements:

High availability and low latency for sending/receiving
Support millions of users and large groups (up to, say, 10k members)
Reasonable consistency guarantees (define what is required)

Discuss:

APIs
Data model/storage
Message fan-out strategy
Ordering guarantees
Offline delivery and retries
Read receipts/typing indicators (optional, but mention tradeoffs)
How you would scale and monitor the system.

Design a group chat system

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Solution

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