Design a Chat for HRT
Last updated: October 31, 2025
Quick Overview
Design a distributed chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
HRT
October 31, 202519
3
1,492 solved
Design a distributed chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
HRT asks this during the System Design Round 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
- 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
- What monitoring and alerting would you set up on day one?
- How would you migrate from a monolithic to a microservices architecture?
- What would the deployment pipeline look like for this system?
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Requirements
Functional Requirements
- User Authentication: Users must be able to sign up, log in, and manage their profiles securely.
- Real-time Messaging: Users should be able to send and receive ...
Capacity Estimation
Assuming HRT anticipates 10 million active users, each sending an average of 10 messages per day:
- Total Messages per Day: 10 million users * 10 messages = 100 million messages/day.
- **Peak Load...
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