Architect a scalable Load Balancing Engine
Last updated: October 14, 2025
Quick Overview
Design a scalable load balancing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Cloudflare
System Design
Product Manager
Cloudflare
October 14, 2025Product Manager
Technical Screen
System Design
Hard
209
14
2,931 solved
Design a scalable load balancing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Cloudflare asks this during the Technical Screen 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
Security and authentication
Load balancing and horizontal scaling
Requirements gathering and capacity estimation
High-level architecture and component design
Partitioning and sharding strategies
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 do you ensure data consistency across multiple services?
- How would you handle a region-wide outage?
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Requirements
- Functional Requirements:
- Traffic Distribution: The load balancer must distribute incoming HTTP/HTTPS requests across multiple backend servers efficiently.
- Health Checks: Re...
Capacity Estimation
- Traffic Estimation:
Assume Cloudflare handles 10 billion requests daily.- Total Requests per Second (RPS) = 10 billion / (24 * 60 * 60) ≈ 115,740 RPS.
- Peak Load: Assume peak traff...
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