How to design a URL Shortener?

These are my notes about how to design a URL shortener.

What is a URL Shortener Service?

• It is for generating shorter aliases for long URLs.
• Common system interview question

Imagine you have an URL like this;

https://www.example.com/ex/testtestestest1.php?a=5&b=4

You will convert to like

https://shorturl.com/y73g2zjl

What are the Requirements

• 1 million URLs are generated per day
• URLs are the combination of [0–9] [a-z, A-Z]
• Generate possibly the shortenest version

Back-of-the-envelope estimation

• Write per second: 1 million / 24 / 3600 = 12
• Read per second: 12 * 10 = 120 (Assuming 10:1)
• After 10 years: 1 million * 365 * 10 = 3.6 billion (3.650.000.000)
• Assume the average URL length is 100 bytes.
• After 10 years: 3.6 billion * 100 bytes = 339.93 Gigabytes

Creating High-Level Design

• We need basically two endpoints. One is for creating a short URL and one is for redirecting to the long version of the URL.

Example Routes