Design a geo-distributed Feature Flag System
Last updated: January 18, 2026
Quick Overview
Design a geo-distributed feature flag system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Cloudflare
January 18, 202617
6
2,180 solved
Design a geo-distributed feature flag 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 optimize costs as the system scales?
- How would you handle a region-wide outage?
- How would you implement rate limiting to protect the system?
- What monitoring and alerting would you set up on day one?
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Requirements
Functional Requirements
- Feature Flag Creation: Allow users to create, update, and delete feature flags through a secure API.
- Geo-Targeting: Enable targeting of feature flags based on...
Capacity Estimation
Back-of-Envelope Calculations
Assuming Cloudflare serves around 1 billion requests daily:
- Requests Per Second (QPS):
- 1 billion requests / 86400 seconds = ~11,574 QPS
- **Storage Requir...
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