Requirements

Functional Requirements:

• The design should accept a valid URL
• The system should shorten the URL and store it in both cache and database
• The server should be able to fetch URL from cache if it's available in it
• In case of cache miss it should be able to fetch it from database
• The server should be able to update the url

Non-Functional Requirements:

• The system should be scalable. We can consider database shading to achieve horizontal scalability.
• Write should main strong consistency while read can be eventually consistent.
• It should be available
• It should have low latency like <100ms for redirects

Capacity Estimation

Estimate the scale of the system. Consider daily active users, read/write ratio, storage requirements, bandwidth, and any relevant QPS calculations...

API Design

Create Short URL:

• Endpoint : POST /api/v1/createShortUrl
• Request Body: { "url": "https://leetcode.com/discuss/interview-question/system-design?currentPage=1&orderBy=hot&query=" }
• Response : {"shortUrl" : ''https://bit.ly/4izy9Dn"}

Redirect to Original URL:

• Endpoint :GET /api/v1/{shortUrl}
• Request Parameteres: {shortUrl}
• Response : Redirect to the Original URL

Update the URL:

• Endpoint : PUT /api/v1/updateShortUrl/{shortUrl}
• Request Parameteres: ```{shortUrl}``
• Request Body : {"url" : ""https://leetcode.com/discuss/interview-question/system-design?currentPage=1&orderBy=hot&query="}
• Response : {"Status : Successfull" , "message : "Short URL updated successfully"}

High-Level Design

Database Design

Define the data model. Identify the main entities, their attributes, and relationships. Consider the choice of database type (SQL vs NoSQL) and justify your decision based on access patterns...

Detailed Component Design

1. Entry layer (MAJOR) — Load balancer + API gateway: handles HTTPS termination, routing, rate limiting before requests hit your services.
2. Write path service (MAJOR) — the Shortener Service: validates the long URL and creates the short code.
3. Read path service (MAJOR) — the Redirect Service: takes a short code, looks it up (cache first), and returns a 302 redirect.
4. Identifier generation (MAJOR) — a strategy to create unique, collision-free short codes (e.g., a dedicated ID generator).
5. Storage layer (MAJOR) — the database persisting short_code → long_url mappings.
6. Cache layer (minor) — Redis in front of the DB for hot redirects.