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:

List the key non-functional requirements (eg low latency, scalability, reliability, etc.)...

API Design

1. Create Short URL (Write Path)

POST /shorten

Request Body:

{

"long_url": "https://example.com/very/long/url",

"custom_alias": "optional_custom_code" // optional

}

Response:

{

"short_url": "https://short.ly/abc123"

}

Description:

• Accepts a long URL and optionally a custom alias.
• Generates the short code.
• Stores mapping in DB.
• Returns the shortened URL.

2. GET /{shorten_URL}

Response:

{

"long_url": "https://example.com/very/long/url",

}

Description:

• Accepts a Short URL
• Checks Mapping in Cacche and if fails then in DB.
• Returns the Long code.

High-Level Design

Overview:

Create short URLs from long URLs.

Redirect short URLs to the original URL.

URL SHORTENING for LONG URL:

Request Flow – Write Path (Short URL Creation)

Client sends POST /shorten request with a long URL.

Load Balancer distributes the request across stateless App Servers.

API Gateway handles routing, authentication, and rate limiting.

ID Generation Service generates a unique short code (Base62 encoding, or distributed ID like Snowflake).

Shortening Service:

• Validates input
• Stores mapping in sharded, replicated database
• Caches the mapping in Redis for fast future reads
• Response: Returns the short_URL.

Redirect SHORTENED URL:

Request Flow – Read PATH (Short URL READ)

Client sends GET /{}reqshort_URL}

Load Balancer distributes the request across stateless App Servers.

API Gateway handles routing, authentication, and rate limiting.

REDIRECT SERVICE looks for short_URL in Cache and if it is there it is returned, otherwise it is queried into database.

Detailed Component Design

Key Architectural Patterns

• Stateless Application Servers → horizontal scaling.
• Caching (Redis) → reduces database load, enables low-latency lookups.
• Sharded & Replicated Database → durability, scalability, and high availability.
• Separation of Concerns → distinct services for URL creation, redirection, and ID generation.