Build a event-driven Ad Serving Pipeline
Last updated: June 11, 2026
Quick Overview
Design a event-driven ad serving system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Expedia
System Design
Machine Learning Engineer
Expedia
June 11, 2026Machine Learning Engineer
Technical Screen
System Design
Medium
7
8
308 solved
Design a event-driven ad serving system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Expedia 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
Monitoring, logging, and alerting
Security and authentication
High-level architecture and component design
Requirements gathering and capacity estimation
Failure handling and fault tolerance
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 optimize costs as the system scales?
- What would the deployment pipeline look like for this system?
- What monitoring and alerting would you set up on day one?
- How would you handle a 10x increase in traffic overnight?
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Requirements
- Functional Requirements:
- Process ad requests in real-time with low latency (under 100ms).
- Serve personalized ads based on user data and context.
- Support A/B testing for ad v...
Capacity Estimation
- Traffic Estimation:
- Assume 10 million requests per minute, translating to approximately 166,667 requests per second (QPS).
- Each request may vary in size, but let’s estimate an aver...
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