Design Load Balancing Infrastructure for global users
Last updated: October 10, 2025
Quick Overview
Design a real-time load balancing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Capital One
System Design
Software Engineer
Capital One
October 10, 2025Software Engineer
Onsite
System Design
Hard
0
15
132 solved
Design a real-time load balancing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Capital One asks this during the Onsite 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
Message queues and async processing
Failure handling and fault tolerance
Monitoring, logging, and alerting
Database selection and data modeling
Requirements gathering and capacity estimation
Load balancing and horizontal scaling
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?
- How would you implement rate limiting to protect the system?
- How would you handle a 10x increase in traffic overnight?
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Requirements
- Functional Requirements:
- The system must balance millions of incoming requests globally across multiple regions.
- It should support real-time request routing based on current load and h...
Capacity Estimation
- User Traffic Estimation: Let's assume Capital One expects 10 million requests per day globally.
- Requests per Second Calculation:
- 10,000,000 requests/day ÷ 86,400 seconds/day = ~115 req...
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