Requirements

Functional Requirements:

Create short URL from a long URL (optional custom alias)

Redirect short code → original long URL

Optional: expiry/TTL, click analytics

Non-Functional Requirements:

High availability (~99.99%) — shared links must never break

Low redirect latency (<100ms p99)

Read-heavy: reads ≫ writes (~100:1)

Horizontal scalability of the stateless read path

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

POST /api/v1/urls Body: { "longUrl": "https://example.com/very/long/path" } Response: 201 { "shortUrl": "https://sho.rt/aB3xK9", "longUrl": "..." } Errors: 400 invalid URL, 409 custom alias taken

GET /{shortCode} Response: 302 Found → Location: https://example.com/very/long/path Errors: 404 unknown code, 410 expired

High-Level Design

Describe the overall system architecture. Identify the main components needed to solve the problem end-to-end. Use the diagramming tool to create a block diagram.

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.