Design a Load Balancing for Cloudflare
Last updated: January 31, 2026
Quick Overview
Design a distributed load balancing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Cloudflare
January 31, 20265
15
4,184 solved
Design a distributed 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
- Systematically gather requirements and estimate capacity (QPS, storage, bandwidth)
- Design a scalable architecture with clear component responsibilities
- Make well-reasoned database and caching decisions with trade-off analysis
- Address consistency vs availability trade-offs specific to the use case
- Discuss partitioning strategy, replication, and data modeling
- Cover failure handling, monitoring, and alerting strategies
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 handle a 10x increase in traffic overnight?
- How would you migrate from a monolithic to a microservices architecture?
- How would you handle schema migrations with zero downtime?
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Requirements
Functional Requirements
- Request Routing: The system should intelligently distribute incoming traffic across multiple servers based on load and health checks.
- Health Monitoring: Conti...
Capacity Estimation
Assuming Cloudflare needs to handle 10 million requests per second (QPS) at peak traffic:
- Total Bandwidth: If each request averages 1 KB of data, this results in 10 TB of data per second.
- ...
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