Architect a low-latency A/B Testing Engine
Last updated: July 20, 2025
Quick Overview
Design a low-latency a/b testing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Morgan Stanley
July 20, 202560
6
4,593 solved
Design a low-latency a/b testing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
This is a common system design question asked during System Design Round at Morgan Stanley. The interviewer expects you to demonstrate your ability to design large-scale distributed systems, make well-reasoned trade-offs, and communicate your thought process clearly. Morgan Stanley values engineers who can think about scalability from day one.
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 handle schema migrations with zero downtime?
- How would you handle a region-wide outage?
- How would you implement rate limiting to protect the system?
- How do you ensure data consistency across multiple services?
Practice a Similar Problem on Codemia
Solve a related problem with our interactive workspace, get AI feedback, and view detailed solutions.
Solve on CodemiaSample Answer
Requirements
- Functional Requirements:
- Ability to create and manage A/B tests with multiple variants.
- Serve requests to users with low latency, ideally under 100 ms.
- Monitor and report metrics, su...
Capacity Estimation
To estimate capacity, we need to consider the scale of Morgan Stanley's operations:
- User Base: Let's assume 1 million active users per day.
- Requests per User: Each user generates approxim...
Submit Your Answer
