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Design A URL Shortener

UberSoftware Engineer · Onsite
MediumSoftware EngineerOnsiteSystem Design

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This question tests your ability to design a high-scale, distributed URL shortening service that handles billions of requests while ensuring low latency and data durability.

System Design: URL Shortener

Design a URL shortening service similar to bit.ly or tinyurl.com. The system should allow users to submit a long URL and receive a unique, shorter alias. When a user navigates to the short URL, they should be redirected to the original long URL.

Requirements

Functional Requirements:

  1. URL Shortening: Given a long URL, generate a unique short alias.
  2. URL Redirection: Given a short alias, redirect the user to the original long URL.
  3. Analytics (Optional/Bonus): Track basic click counts for shortened URLs.
  4. Custom Aliases: Allow users to pick a custom short alias.

Non-Functional Requirements:

  1. Scalability: The system must handle high read/write traffic (e.g., 100 million new URLs per day, 1 billion redirects per day).
  2. Latency: Redirection must be extremely fast (under 100ms).
  3. Durability: Shortened URLs must not be lost.
  4. Availability: The service should remain highly available under heavy load.

Deliverables

Your response should include:

  • API Design: Define the endpoints for creating and resolving URLs.
  • Data Model: Choose between SQL or NoSQL and explain why.
  • Architecture: Provide a high-level design including load balancers, application servers, storage, and caching layers.
  • Generation Strategy: Explain how you will generate unique short codes and handle collisions.
  • Trade-offs: Discuss how you handle high read volume versus write volume and how you maintain consistency.

Hints

Hint 1

Consider using a distributed key generation service or hashing approach to create unique identifiers without needing to check for collisions constantly.

Hint 2

Think about where a caching layer would be most effective to reduce database load for the most popular URLs.

Hint 3

Address the choice of database by considering the specific read/write patterns and the need for horizontal scaling.

Follow-up questions

  • How would you handle the deletion or expiration of shortened URLs after a certain period?
  • How would you protect the system from malicious use, such as massive scraping or shortening URLs that point to malware?
  • If you were tasked with tracking geolocation data for each click, how would you design the analytics pipeline to ensure it doesn't impact redirection latency?