Design a Chat for Airbnb

Last updated: May 15, 2026

Quick Overview

Design a real-time chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.

Airbnb
System Design
Machine Learning Engineer
Airbnb
May 15, 2026
Machine Learning Engineer
Technical Screen
System Design
Easy

1

11

2,614 solved

Design a real-time chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.

Airbnb asks this during the Technical Screen to assess your architectural thinking. They want to see how you decompose a complex problem, choose appropriate technologies, and reason about failure modes. Strong candidates proactively discuss monitoring, alerting, and operational concerns.

What the Interviewer Expects
  • Clearly define functional and non-functional requirements
  • Propose a reasonable high-level architecture with core components
  • Choose appropriate data storage solutions with basic justification
  • Discuss basic scaling strategies (horizontal scaling, caching)
  • Identify potential bottlenecks and suggest simple solutions
Key Topics to Cover
Partitioning and sharding strategies
Requirements gathering and capacity estimation
API design and rate limiting
Caching strategies (local, distributed, CDN)
Load balancing and horizontal scaling
Message queues and async processing
How to Approach This
  1. Start by clarifying functional and non-functional requirements with the interviewer.
  2. Estimate the scale: QPS, storage, bandwidth. This drives your design decisions.
  3. Draw a high-level architecture first, then deep dive into 1-2 critical components.
  4. Discuss trade-offs explicitly (e.g., consistency vs availability, SQL vs NoSQL).
  5. Address failure scenarios, monitoring, and how the system handles 10x traffic spikes.
Possible Follow-up Questions
  • How would you optimize costs as the system scales?
  • How would you implement rate limiting to protect the system?
  • What happens if one of your database nodes goes down?
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Sample Answer
Requirements
  • Functional Requirements:
    1. Real-time messaging between hosts and guests.
    2. Support for sending text, images, and links.
    3. User presence indicators (online/offline).
    4. Searcha...
Capacity Estimation

To estimate capacity, we consider the following:

  1. User Base: Assume Airbnb has 100 million users.
  2. Active Users: Roughly 10% (10 million) are active at any given time.
  3. **Messages ...
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Airbnb Machine Learning Engineer Interview Guide

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