Architect a real-time URL Shortening Engine
Last updated: December 22, 2025
Quick Overview
Design a real-time url shortening system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Brex
System Design
Software Engineer
Brex
December 22, 2025Software Engineer
Technical Screen
System Design
Medium
3
14
4,245 solved
Design a real-time url shortening system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Brex 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
Partitioning and sharding strategies
High-level architecture and component design
Load balancing and horizontal scaling
Caching strategies (local, distributed, CDN)
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?
- What happens if one of your database nodes goes down?
- How would you handle schema migrations with zero downtime?
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Requirements
Functional Requirements
- URL Shortening: Users can input a long URL and receive a shortened version.
- Redirection: Users can access the original URL by visiting the shortened URL.
- *...
Capacity Estimation
Back-of-Envelope Calculations
- Estimated Daily Requests: Assume 10 million requests per day, translating to about 115 requests per second (QPS).
- Storage Estimation: If each URL mappin...
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