Requirements

Functional Requirements:

• Generate a short url from long url.
• Redirect Short Url to Original Url.
• Support Custom Aliases.
• Support Link Expiration.

Non-Functional Requirements:

• High Availability (redirect must always work)
• Low Latency (<100 ms for redirect)
• High Scalability (millions of users)
• Read-Heavy System (redis >> writes)

Assumptions

• 1M Urls created per day.
• 100M redirects per day.
• URL Size ~500 bytes

API Design

• Create Short URL

URL:- POST /shorten

Request:- {

"long_url": "https://example.com/abc",

"custom_alias": "myurl", // optional

"expiry": "2026-12-31" // optional

}

Response:-

{

"short_url" : "https://tinyurl.com/abc123"

}

• Redirect API

URL: -GET /{short_code}

Response:- HTTP 301 Redirect -> Original URL

• Analytics API

URL:- GET /analytics/{short_code}

High-Level Design

• Architecture Flow

Client -> Load Balancer -> API Servers -> Cache -> Database

• Components

Load Balancer

• Distributes Traffic

API Servers (Node.js)

• Handle Request
• Generate Short URLs

Cache (Redis)

• Stores Frequently Accessed URLs
• Reduces DB Load

Database (MYSQL/NOSQL)

• Stores Permanent Mappings

• Request Flow

Redirect Flow

1. User Clicks on Short URL.
2. Check Redis
3. If miss -> query DB
4. Store in Redis
5. Redirect User

System is read-heavy. Cache is critical.

Detailed Component Design

• URL Generation Service

Handles ID + Base 62

Handles Collisions

Supports Custom Alias

• Redirect Service

Cache-first lookup

DB Fallback

301 Redirect

• Cache Layer

Cache-aside strategy

TTL + LRU

Stampede Protection Using Locks

• DataBase Layer

Key-Value Mapping

Indexed by short_code

Sahrding + Replicas

• API Layer

Node.js Servers

Load Balanced

Stateless

• Additional Components

Rate Limiting

Analytics

Async Processing