Design Load Balancing Infrastructure for global users
Last updated: September 19, 2025
Quick Overview
Design a fault-tolerant load balancing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Brex
System Design
Software Engineer
Brex
September 19, 2025Software Engineer
Onsite
System Design
Hard
13
9
1,515 solved
Design a fault-tolerant load balancing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Brex 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
Partitioning and sharding strategies
Monitoring, logging, and alerting
Caching strategies (local, distributed, CDN)
High-level architecture and component design
Failure handling and fault tolerance
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 schema migrations with zero downtime?
- How would you optimize costs as the system scales?
- How would you handle a 10x increase in traffic overnight?
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Requirements
- Functional Requirements:
- Handle millions of incoming requests per second from global users.
- Route requests to the nearest available service instance based on user location.
- ...
Capacity Estimation
- User Base: Assume Brex has 10 million active users globally.
- Request Rate: Each user generates approximately 5 requests per day on average.
- Total Requests: 10 million users * 5 r...
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