How do I approach System Design interview questions?

System Design questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master system design interviews.

What difficulty level is this interview question?

This is a hard difficulty System Design question, commonly asked during Onsite rounds at Airbnb.

What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Airbnb during technical interviews.

Design a real-time chat system with hot groups

Quick Overview

This question evaluates system design and real-time distributed systems skills, including designing scalable chat architectures that support 1:1 and group conversations, WebSocket-based delivery and routing across multiple gateway servers, message persistence and history sync, multi-device consistency and read receipts, plus the ability to define, detect and optimize for the Top N "hot" group chats. Commonly asked to assess reasoning about high-level architecture, concrete data schema and indexing, routing and state synchronization, and availability/disaster-recovery trade-offs, it tests both conceptual understanding and practical application by requiring a clear architecture together with detailed data model and scalability/performance considerations.

Design a real-time chat system (similar to an in-app messaging feature) that supports:

1:1 and group conversations
Real-time delivery over WebSockets (or equivalent)
Message persistence and history sync
Read receipts (at least per-user “last read”)
Multi-device users (same user logged in on multiple clients)
High availability / disaster recovery considerations

Additional requirement:

The system must optimize for the Top N “hottest” group chats (e.g., groups with extremely high message throughput and/or many concurrently online participants). Explain what “hot” means and how you detect it.

The interviewer expects particular attention to:

A clear high-level architecture
A concrete data schema (tables/collections, keys, indexes)
How messages get routed when you have multiple WebSocket gateway servers
Scalability and performance trade-offs

Quick Overview

Design a real-time chat system (similar to an in-app messaging feature) that supports:

1:1 and group conversations
Real-time delivery over WebSockets (or equivalent)
Message persistence and history sync
Read receipts (at least per-user “last read”)
Multi-device users (same user logged in on multiple clients)
High availability / disaster recovery considerations

Additional requirement:

The system must optimize for the Top N “hottest” group chats (e.g., groups with extremely high message throughput and/or many concurrently online participants). Explain what “hot” means and how you detect it.

The interviewer expects particular attention to:

A clear high-level architecture
A concrete data schema (tables/collections, keys, indexes)
How messages get routed when you have multiple WebSocket gateway servers
Scalability and performance trade-offs

Design a real-time chat system with hot groups

Quick Overview

Solution

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Design a real-time chat system with hot groups

Quick Overview

Solution

Comments (0)