Requirements

Functional Requirements:

• Map a long url to short url
• No authentication
• Rate limiting to avoid throttling
• Generate short url in base62
• No updates
• No delete
• Automatic Expiry TTL
• Should handle 404 error
• Job to purge expired rows
• Validate url schema
• Job to sweep unexisted long url map

Non-Functional Requirements:

• Latency: Reads < 100ms, Write < 100ms
• 116K reads/sec, 1.2k writes/sec
• System must have strong availability
• Caching for performance

• Reads: ~116K/sec
• Writes: ~1.2K/sec
• Storage: 100M new rows/day (each a few hundred bytes → tens of GB/day)

API Design

We basically just have 2 endpoints.

Let's design as a REST API

• POST Request: Create short url
• GET: Returns a 3xx status code for redirect

High-Level Design

Let's design it simple.

Let's add 2 server instances with a load balancer between the client and the servers.

The servers first call a cache database like redis (we can have a replica for redundancy).

Probably we can use Cache on Write approach so the cache database is always in sync with the persistent database (can be postgres)

So when client creates a short url and other client gets, we know we can have a cache hit.

The persisted database can have also a replica

Database Design

Primary key: id

source_url: string

short_url: string

created_at: timestamp

expire_at: timestamp

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.