System Design FAQ: Top Questions

A URL Shortener takes long URLs and generates short, redirectable aliases (e.g., bit.ly/abc123). It must support high read throughput, efficient redirection, and optional analytics.

📋 Functional Requirements

• Shorten long URL to a unique short URL
• Redirect short URL to original long URL
• Support custom alias input
• Optional: expiration, click analytics

📦 Non-Functional Requirements

• Low-latency redirection (<10ms)
• Globally unique alias generation
• Highly available and horizontally scalable

🏗️ Core Components

• Shorten API: Accepts long URL and returns short alias
• Redirector Service: Resolves alias to original and HTTP 302
• Storage: Key-value DB or RDBMS
• Analytics Collector: Logs redirects, user agents, IPs (optional)

🧮 ID Generation Strategy

• Use base62 encoding of auto-increment integer or UUID
• Random 6-8 character string hashed via MurmurHash, etc.

🗄️ Schema for PostgreSQL

CREATE TABLE short_urls (
  id SERIAL PRIMARY KEY,
  alias VARCHAR(10) UNIQUE,
  long_url TEXT NOT NULL,
  created_at TIMESTAMP DEFAULT now(),
  expires_at TIMESTAMP
);
        

⚙️ Base62 Encoding Example (Python)

import string

BASE62 = string.digits + string.ascii_letters

def encode(n):
    s = []
    while n > 0:
        n, r = divmod(n, 62)
        s.append(BASE62[r])
    return ''.join(reversed(s))
        

🔁 Redirect Handler (Node.js)

app.get('/:alias', async (req, res) => {
  const original = await db.get(req.params.alias);
  if (original) {
    res.redirect(302, original);
  } else {
    res.status(404).send('Not found');
  }
});
        

📈 Observability

• Clicks per alias
• Redirect latency
• Alias collision rate

🧰 Tools/Infra Used

• DB: PostgreSQL, DynamoDB, Redis
• Frontend: Nginx + Flask/Express
• Click Tracker: Kafka + batch ETL

📌 Final Insight

A robust URL shortener should generate short aliases with low collision risk, support expiration logic, and provide fast lookup and redirection via an optimized key-value layer.