System Design FAQ: Top Questions

A URL Shortener maps long URLs to short aliases. It's widely used for improving link readability, analytics, and character-saving (e.g., Twitter).

📋 Functional Requirements

• Generate short unique keys for long URLs
• Redirect short URLs to original long URLs
• Track usage analytics (clicks, referrers)
• Support custom aliases

📦 Non-Functional Requirements

• High availability and low-latency redirection
• Idempotent key generation (same URL maps to same key optionally)
• Expiration and deletion of links

🏗️ Core Components

• API Server: Accepts long URLs and returns short aliases
• Key Generator: Encodes URL or uses hash/ID space
• Redirector: Handles high-throughput redirects
• Analytics Tracker: Stores visit metrics

🔑 Base62 Encoding (Python)

import string

CHARSET = string.digits + string.ascii_letters

def encode(num):
    base = 62
    s = []
    while num > 0:
        s.append(CHARSET[num % base])
        num = num // base
    return ''.join(reversed(s)) or '0'
        

🔧 Example Redis Key-Value Mapping

SET short:abc123 "https://verylongsite.com/user/onboarding?id=983"
EXPIRE short:abc123 31536000  # 1 year
        

📥 Sample API

POST /shorten
{
  "long_url": "https://openai.com/research/chatgpt"
}

Response:
{
  "short_url": "https://sho.rt/x9Bz4A"
}
        

📈 Analytics Schema (Click Log)

{
  "short_code": "x9Bz4A",
  "clicked_at": "2025-06-11T10:15:00Z",
  "ip": "45.23.19.88",
  "user_agent": "Mozilla...",
  "referrer": "https://twitter.com"
}
        

🔐 Custom Alias Handling

• Allow user to reserve codes like https://sho.rt/promo2025
• Reject duplicates with 409 Conflict

📊 Admin Panel Features

• Top-performing links
• Expiration date manager
• Click-through analytics and referrer pie chart

📈 Observability

• Short link resolution latency
• 404 rates (invalid code hits)
• Most clicked links in time window

🧰 Tools/Infra Used

• Store: Redis / DynamoDB / PostgreSQL
• Tracking: Kafka + OLAP store (ClickHouse)
• Web server: FastAPI / Node.js / Go

📌 Final Insight

URL shorteners are deceptively simple but must be scalable, analytics-ready, and collision-safe. Encoding strategy, rate of generation, and efficient redirection paths are key to success.