Build a fault-tolerant A/B Testing Pipeline
Last updated: January 25, 2026
Quick Overview
Design a fault-tolerant a/b testing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Grubhub
January 25, 202618
14
1,389 solved
Design a fault-tolerant a/b testing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Grubhub 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
- 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
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
- What would the deployment pipeline look like for this system?
- What happens if one of your database nodes goes down?
- How do you ensure data consistency across multiple services?
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Requirements
Functional Requirements
- User Management: Support user authentication and authorization to ensure only authorized personnel can manage A/B tests.
- Experiment Creation: Allow product ma...
Capacity Estimation
Assuming Grubhub handles approximately 1 million orders per day:
- Requests per second (QPS):
- 1,000,000 orders/day / 86400 seconds/day = ~11.6 QPS
- With A/B testing, assume 10% of traffic ...
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