Design a large-scale Feature Flag Platform
Last updated: October 8, 2025
Quick Overview
Design a geo-distributed feature flag system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Jane Street
System Design
Software Engineer
Jane Street
October 8, 2025Software Engineer
System Design Round
System Design
Medium
5
5
1,352 solved
Design a geo-distributed feature flag system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Jane Street typically last 45-60 minutes. You are expected to drive the conversation, starting from requirements gathering through to a detailed architecture. The interviewer will evaluate your ability to handle ambiguity and make practical engineering decisions.
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
API design and rate limiting
Load balancing and horizontal scaling
Partitioning and sharding strategies
Caching strategies (local, distributed, CDN)
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 migrate from a monolithic to a microservices architecture?
- How would you handle a region-wide outage?
- What monitoring and alerting would you set up on day one?
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Requirements
- Functional Requirements:
- Ability to create, update, and delete feature flags for different environments (development, staging, production).
- Support for targeting flags to specific user s...
Capacity Estimation
- Estimated Traffic:
- Assume 10 million requests per day, translating to around 115 requests per second (QPS).
- Peak traffic may reach up to 5x the average, especially during rollouts, leadi...
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