Design a real-time Feature Flag System
Last updated: March 13, 2026
Quick Overview
Design a real-time feature flag system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Tesla
March 13, 202610
10
1,229 solved
Design a real-time feature flag system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Tesla asks this during the Onsite 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
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?
- What would the deployment pipeline look like for this system?
- What happens if one of your database nodes goes down?
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Requirements
- Functional Requirements:
- Ability to create, update, and delete feature flags in real-time.
- Support for targeting flags to specific user groups, devices, or geographic locations.
- Abil...
Capacity Estimation
To estimate the capacity for the feature flag system:
- Assume Tesla has around 1 million active users who can trigger features.
- If each user can send an average of 10 flag requests per day, that t...
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