Design a large-scale Feature Flag Platform
Last updated: July 27, 2025
Quick Overview
Design a geo-distributed feature flag system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Roblox
July 27, 2025127
4
4,713 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 Roblox 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
- 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
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 implement rate limiting to protect the system?
- What monitoring and alerting would you set up on day one?
- How would you handle a region-wide outage?
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Requirements
Functional Requirements
- Feature Management: Ability to create, read, update, and delete feature flags.
- Targeting Rules: Define rules for enabling flags based on user attributes (e.g....
Capacity Estimation
Assuming Roblox has approximately 100 million active users, and each user makes an average of 10 feature flag checks per day:
- Daily Requests: 100 million users * 10 checks = 1 billion requests ...
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