Design a URL Shortening Service
Last updated: January 25, 2026
Quick Overview
Design a low-latency url shortening system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Slack
January 25, 20267
5
1,572 solved
Design a low-latency url shortening system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
ML system design at Slack goes beyond model selection. This Technical Screen question evaluates your ability to design end-to-end ML pipelines, from data collection to model serving, while considering production constraints like latency and reliability.
What the Interviewer Expects
- Map the business problem to a concrete ML objective
- Propose reasonable features and a baseline model
- Discuss basic model evaluation metrics
- Outline a simple serving architecture
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 you do if model performance degrades over time?
- How would you ensure fairness and reduce bias in the model?
- How would you handle a 10x increase in prediction requests?
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Requirements
Functional Requirements
- URL Shortening: Users can input a long URL and receive a unique short URL.
- Redirection: When a short URL is accessed, it should redirect to the original long ...
Capacity Estimation
Assuming Slack has approximately 10 million users and each user shortens an average of 5 URLs per month:
- Total Shortened URLs: 10,000,000 users * 5 URLs/user = 50,000,000 URLs/month.
- **Daily A...
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