Design a large-scale Chat Platform
Last updated: February 17, 2026
Quick Overview
Design a scalable chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Grubhub
February 17, 20261
9
2,604 solved
Design a scalable chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Grubhub typically last 45-60 minutes. You are expected to drive the conversation, starting from requirements gathering through to a detailed architecture. The interviewer will evaluate your ability to handle ambiguity and make practical engineering decisions.
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
How to Approach This
- Start by clarifying functional and non-functional requirements with the interviewer.
- Estimate the scale: QPS, storage, bandwidth. This drives your design decisions.
- Draw a high-level architecture first, then deep dive into 1-2 critical components.
- Discuss trade-offs explicitly (e.g., consistency vs availability, SQL vs NoSQL).
- 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?
- What happens if one of your database nodes goes down?
- What monitoring and alerting would you set up on day one?
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Requirements
- Functional Requirements:
- Users should be able to send and receive messages in real-time.
- Support for 1-on-1 and group chats.
- Message history retrieval for previous conversat...
Capacity Estimation
Assuming Grubhub has about 30 million users, we can estimate:
- Average messages per user per day: 10
- Total messages per day: 30M users * 10 messages = 300M messages/day
- Average message s...
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