Requirements

Functional Requirements:

1. Create short URL - given a long URL, generate a unique short alias
2. Redirect - given a short URL, return the original long URL and redirect the user
3. Custom alias - allow users to pick a readable alias
4. Expiration - support optional TTL so links expire
5. Delete/update - let the owner remove or repoint a short link
6. Analytics - track click counts per short URL

Non-Functional Requirements:

1. High availability - the redirect must never fail even if a server dies
2. Low redirect latency - sub-100ms; the write path can be slower, the read path must be fast
3. Horizontal scalability - handle millions of reads/day by adding more servers

Capacity Estimation

• 100M new URLs/day (writes)
• Read:write ratio = 100:1 (typical for URL shorteners)
• Long URL ≈ 500 bytes avg; each DB record ≈ 1KB with metadata

Traffic / QPS

• Writes: 100M / 86400 = 1158 w/s
• Reads: 115741 r/s
• Peak: 348K r/s

Storage

• 100M * 1KB = 100 GB/day
• 5-year retention: 100 GB * 365 * 5 = 180TB

Cache

• Cache hot URLS: 20M * 500B = 10GB

API Design

POST /api/urls

Request:

{

"longUrl" : "string (required)",

"customAlias" : "string (optional)",

"expiresAt" : "datetime (optional)"

}

Response: 201 -> {"shortUrl"}

GET /api/urls/{shortURL}

Response: 302 -> {LongUrl}

DELETE /api/urls/{shortURL}

GET /api/urls/{shortUlr}/stats

PUT /api/urls/

High-Level Design

This architecture consists of the following components:

1. The system client itself - the primary user who wants to get a short link to their long URL

2. CDN - to speed up operation

3. Load Balancer - to protect the system from overload and ensure continuous server availability

4. API Gateway - a single entry point, added for routing and system security

5. Rate Limiter - a service that checks whether the short link has expired

6. Shortener Service - a service for creating, editing, and deleting short URLs

7. Redirect Service - a service responsible for redirecting a short URL to the original long URL

8. Shortener Service and Redirect Service - both use Cache to quickly find URLs; if they are not in the cache, they attempt to work with them through the Database

9. ID Generation Service - is used to generate a hash of identifiers for working with short URLs.

10. Analytics Service - an analytics service that tracks clicks on short URLs. The Shortener Service and Redirect Service send data to it

11. Database — the source of truth for all short_code → long_url mappings; absorbs all writes; the cache sits in front of it to serve the read-heavy traffic

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

Deep dive into 2-3 key components. Explain how they work, how they scale, discuss tradeoffs, capacity, and any relevant algorithms or data structures.