Design A/B Testing Infrastructure for global users
Last updated: October 8, 2025
Quick Overview
Design a high-throughput a/b testing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
LinkedIn
System Design
Software Engineer
Software Engineer
System Design Round
System Design
Medium
1
4
4,474 solved
Design a high-throughput a/b testing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at LinkedIn 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
Security and authentication
Failure handling and fault tolerance
Database selection and data modeling
High-level architecture and component design
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 implement rate limiting to protect the system?
- How would you optimize costs as the system scales?
- How do you ensure data consistency across multiple services?
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Requirements
- Functional Requirements:
- Ability to create, manage, and analyze A/B tests for various features on LinkedIn.
- Provide APIs for experiment creation, user assignment, and result retrieval....
Capacity Estimation
- User Base: Assume LinkedIn has 900 million users worldwide.
- Active Users: Estimate 20% are active daily, which equals 180 million users.
- A/B Tests: Assume 10% of these users will be ...
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