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:

• Scalable to 100k+ users
• Low latency for short URL to long conversion when calling API
• Availablility much priority over consistency

API Design

POST /shorten

Request : {longURL}

Response : {shortURL}

GET /{shortCode}

Redirect to original URL

High-Level Design

Load Balancer

• Distributes traffic
• Health checks
• Avoids single point of failure

App Servers

• Stateless
• Handle shortening logic
• Handle redirects

Database

• Stores mapping: shortCode → longURL

Detailed Component Design

Database:

SQL or NoSQL?

• We mostly do key-value lookup.
• No complex joins.
• Massive reads.
• Need horizontal scaling.

Better: NoSQL (like DynamoDB/Cassandra)

Or even Redis + persistent store.

Redirect Flow

User hits:

short.ly/abc123

Flow:

1. Load Balancer
2. App Server
3. DB lookup
4. Return 301 redirect

Because read-heavy, we add caching.

Flow:

1. Check Redis
2. If hit → return
3. If miss → fetch from DB
4. Store in Redis

This reduces DB load massively.