Design a real-time Chat System
Last updated: August 16, 2025
Quick Overview
Design a real-time chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Anduril
August 16, 20250
4
1,163 solved
Design a real-time chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Anduril 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
- 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 implement rate limiting to protect the system?
- How would you optimize costs as the system scales?
- What would the deployment pipeline look like for this system?
- What monitoring and alerting would you set up on day one?
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Requirements
Functional Requirements:
- User Authentication: Users must be able to securely sign up, log in, and manage their accounts.
- Real-time Messaging: Users should be able to send and receive...
Capacity Estimation
Assuming Anduril expects to support 10 million active users:
- Each user sends approximately 10 messages per hour.
- Total messages per hour = 10 million users * 10 messages = 100 million messages.
- ...
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