Design a Distributed URL Shortener (TinyURL / Bit.ly).

In Simple Words: Design a scalable service that converts long URLs (e.g. 150 characters) into concise aliases (e.g. https://tiny.cc/a8X9k2) and redirects users with sub-15ms latency.

Scale Estimations:

• Traffic: 100M new URLs created per month (~40 writes/sec), 10B redirects per month (~4,000 reads/sec → 100:1 Read-Heavy).
• Storage: 100M URLs × 500 bytes per record × 12 months × 5 years = 3 TB total storage (easily manageable).
• Base62 Character Set: [a-zA-Z0-9] (62 characters).
  • Length 6: $62^6 \approx 56.8$ Billion combinations.
  • Length 7: $62^7 \approx 3.5$ Trillion unique combinations (safely covers 100 years).

flowchart TD
    Client["User Browser"] -->|"1. GET /a8X9k2"| CDN["Edge CDN / Cloudflare"]
    CDN -->|"Cache Miss"| LB["Load Balancer"]
    LB --> WebApp["URL Redirection Service"]
    WebApp --> Redis["Redis Cluster (LRU Hot Cache)"]
    Redis -.->|"Cache Miss"| DB["NoSQL Storage (DynamoDB / Cassandra)"]
    WebApp -->|"301 / 302 Redirect"| Client

// Base62 Converter for Distributed Unique Integer IDs
const BASE62_CHARS = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';

export function encodeBase62(num: bigint): string {
  if (num === 0n) return '0';
  let str = '';
  let n = num;
  while (n > 0n) {
    const rem = Number(n % 62n);
    str = BASE62_CHARS[rem] + str;
    n = n / 62n;
  }
  return str;
}