Design a large-scale Chat Platform
Last updated: September 11, 2025
Quick Overview
Design a low-latency chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Lyft
September 11, 202515
11
1,454 solved
Design a low-latency chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
This is a common system design question asked during Technical Screen at Lyft. The interviewer expects you to demonstrate your ability to design large-scale distributed systems, make well-reasoned trade-offs, and communicate your thought process clearly. Lyft values engineers who can think about scalability from day one.
What the Interviewer Expects
- Drive the design discussion proactively with minimal interviewer guidance
- Perform detailed capacity estimation and use it to inform design decisions
- Design for global scale with multi-region deployment and data consistency
- Deep dive into 2-3 critical components with implementation-level detail
- Address complex trade-offs: CAP theorem, eventual consistency, conflict resolution
- Discuss operational excellence: deployment strategy, chaos engineering, SLOs/SLIs
- Propose a phased rollout plan from MVP to full-scale system
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 handle a region-wide outage?
- What monitoring and alerting would you set up on day one?
- How would you handle schema migrations with zero downtime?
- What would the deployment pipeline look like for this system?
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Requirements
Functional Requirements:
- Real-Time Messaging: Users should be able to send and receive messages in real time with minimal latency.
- Group Chats: Support for one-on-one and group chat ...
Capacity Estimation
Estimation Calculations:
- User Base: Assume 10 million active users with 1 message sent per user per hour.
- Message Volume: 10 million messages/hour translates to about 2,800 messages/...
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