Requirements

Functional Requirements:

• Create a short URL for a given long URL.
• Return the long URL associated with a given short URL.

Non-Functional Requirements:

• There should be no collisions between two short urls for different long urls
• The same short url should always lead to the corresponding long url and should be persisted
• High availability
• Low latency
• Horizontal scaling

API Design

There should be two endpoints

- POST /shorten checks for existing short url for given long one and creates a short url

- GET /long looks up the given short url and returns the long version

High-Level Design

The short and long url pairs are stored in a relational database while a key value store handles the caching. The server checks the cache and if found redirects otherwise it checks the DB and updates the cache. There needs to be a DB replication in case of outage.

Detailed Component Design

The shorten API uses an base64 encoding to create shorter urls.

The relational DB should only be used if there is a cache miss. If one DB goes down the replica should be used instead.