How would you build TinyURL?

Building a URL shortener like TinyURL involves several key components:

1. URL Shortening Service: This is the core logic. When a user submits a long URL, the service generates a unique, short alias (e.g., tinyurl.com/abcde). This can be done by:

   • Hashing: Using a hash function (like MD5 or SHA-1) on the long URL and taking a portion of the hash to create the short alias. Collisions need to be handled.
   • Counter-based approach: Using a base-62 (0-9, a-z, A-Z) encoding of an auto-incrementing ID. Each new URL gets a unique ID, which is then encoded into a short string.

2. Database: A persistent store is needed to map short URLs to their original long URLs. This could be a relational database (like PostgreSQL or MySQL) or a NoSQL database (like Cassandra or DynamoDB) for scalability. The schema would typically include short_url_key and long_url.

3. Web Server/API: This handles user requests. It will have endpoints for:

   • Creating a short URL (POST /shorten).
   • Redirecting from a short URL to a long URL (GET /{short_url_key}).

4. Caching: To improve read performance and reduce database load, a caching layer (like Redis or Memcached) can store frequently accessed short-to-long URL mappings.

5. Scalability Considerations:

   • Database Sharding: Distribute data across multiple database servers.
   • Load Balancing: Distribute incoming traffic across multiple web servers.
   • Asynchronous Processing: For tasks like generating unique IDs or updating analytics, use message queues.

6. API Design: The API should be simple and RESTful. For example:

   • POST /api/v1/shorten with a JSON body like {"url": "https://example.com/very/long/url"} returning {"short_url": "tinyurl.com/abcde"}.
   • GET /abcde for redirection.

7. Analytics (Optional): Tracking clicks, referrers, and geographic data for each short URL.