Design Ad Serving Infrastructure for IoT devices
Last updated: January 20, 2026
Quick Overview
Design a distributed ad serving system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Expedia
January 20, 20266
6
1,548 solved
Design a distributed ad serving system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
This is a common system design question asked during Technical Screen at Expedia. 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. Expedia values engineers who can think about scalability from day one.
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
- How would you implement rate limiting to protect the system?
- How would you handle a region-wide outage?
- What would the deployment pipeline look like for this system?
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Requirements
Functional Requirements
- Ad Serving: The system should serve personalized ads to IoT devices based on user preferences and device context.
- User Tracking: Capture user interactions wit...
Capacity Estimation
- Request per Second (QPS): Assume each IoT device sends 1 ad request every minute. With 10 million active devices, we get:
- 10,000,000 devices * 1 request/minute = 166,667 QPS.
- **Storage ...
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