Design a group chat system
Company: Airbnb
Role: Software Engineer
Category: System Design
Difficulty: medium
Interview Round: Technical Screen
## System Design: Group Chat
Design a scalable group chat system (like a basic Slack/WhatsApp group chat).
### Core features
- Users can create groups, join/leave groups, and manage membership.
- Users can send messages to a group and receive messages on multiple devices.
- Store message history and allow fetching recent messages.
### Non-functional requirements
- Low latency message delivery.
- High availability and horizontal scalability.
- Reasonable ordering guarantees within a group.
Explain:
- APIs
- Data model / storage
- Real-time delivery mechanism
- How you scale (sharding/partitioning)
- How you handle offline users and multi-device sync
- Tradeoffs (fanout, ordering, consistency)
Quick Answer: This question evaluates system design and distributed-systems competencies including real-time messaging architecture, API design, data modeling and storage, scalability (sharding/partitioning), fault tolerance, ordering and consistency guarantees, and multi-device/offline synchronization.