System Design - Design a URL Shortener

System Design - Design a URL Shortener

A URL shortener converts long URLs into shorter aliases that redirect to the original. Services like Bit.ly and TinyURL have made this a classic system design interview question—it's accessible enough for a wide range of candidates, but also offers depth for those with more experience.

Problem Statement

Design a URL shortener system that takes a long URL and returns a short URL. The short URL should be unique, easy to remember, and should redirect to the original URL when accessed.

Examples

1. Input: http://www.example.com/very/long/url Output: http://short.url/abc

2. Input: https://www.google.com/search?q=system+design Output: http://short.url/123

Constraints

1. The system should handle a large number of requests per second.
2. The system should be highly available and fault-tolerant.
3. The system should be able to handle a large number of URLs.
4. The system should be able to resolve short URLs to their original URLs quickly.

Hints

1. Consider using a database to store the mapping between short URLs and original URLs.
2. Think about how to generate unique short URLs.
3. Consider using caching to improve performance.
4. Think about how to handle edge cases, such as invalid URLs or duplicate URLs.

Solution

A high-level solution for designing a URL shortener system can be broken down into the following components:

1. URL Generation: Generate a unique short URL for each long URL. This can be done using various techniques, such as:

   • Hashing the long URL and taking a substring of the hash.
   • Using a counter or database sequence to generate a unique ID.
   • Using a base62 encoding to shorten the ID.

2. Database: Store the mapping between short URLs and original URLs in a database. This can be a relational database like MySQL or a NoSQL database like Redis or MongoDB.

3. Caching: Use caching to improve performance and reduce database load. Redis can be used as an in-memory data store to cache frequent requests.

4. Load Balancing: Use a load balancer to distribute incoming requests across multiple servers, ensuring high availability and fault tolerance.

5. Redirection: When a short URL is accessed, the system should quickly resolve it to the original URL and redirect the user.

6. Edge Cases: Handle edge cases such as invalid URLs, duplicate URLs, and rate limiting to prevent abuse.

This is a high-level overview of the system design. Each component can be further细化 and optimized based on specific requirements and constraints.