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Design a URL shortener

J.P. MorganSoftware Engineer · Technical Screen
MediumSoftware EngineerTechnical ScreenSystem Design

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This question assesses the ability to design a distributed URL shortening service, focusing on database schema design, collision resolution, and caching strategies for high-read throughput.

System Design: URL Shortener

Design a service similar to Bitly that takes a long URL and returns a shorter, unique alias (e.g., bit.ly/xyz123). The system needs to support high read traffic (redirects) and moderate write traffic (creating new links).

Functional Requirements

  1. Shorten: Given a long URL, generate a unique, shorter URL.
  2. Redirect: Given a short URL, redirect the user to the original long URL.
  3. Analytics (Optional): Basic tracking of total redirect count.

Non-Functional Requirements

  1. High Availability: The redirect service must be fast and reliable.
  2. Scalability: The system should support billions of URLs.
  3. Latency: Redirects should happen with minimal latency (ideally < 100ms).

Expectations

  • API Design: Define the request/response structure for the shortening and redirect endpoints.
  • Data Model: Propose a database schema (SQL vs. NoSQL) and explain why.
  • Algorithm: Explain how you will generate the short key (e.g., hashing, base conversion, or centralized counter).
  • High-level Architecture: Describe the components (Load Balancer, Web Servers, Database, Caching layer) and how they interact.
  • Scalability: How do you handle a scenario where a specific URL becomes viral?

Hints

Hint 1

Consider using Base62 encoding to map a numeric ID to a short string to minimize key length.

Hint 2

Decide whether you want to use a distributed database like Cassandra or a relational one like MySQL, keeping in mind the need for high-speed primary key lookups.

Hint 3

Think about where to place a cache (like Redis) to reduce the load on the database for frequently accessed URLs.

Follow-up questions

  • How would you handle the deletion or expiration of links?
  • If two users provide the same long URL, should they get the same short URL, and how would you manage that?
  • How would you evolve this system to support custom aliases (e.g., bit.ly/my-cool-link)?