System requirements

Functional:

• should shorten the urls to 8 char length of the new string
• should not have duplicate shortened URLs
• shortened URLs should expire after a while (e.g 3 months)
• provided URLs should be consistently available
• authorization should not be required for non-enterprise customers
• for people accessing to the URL authZ should not be required

Non-Functional:

• the service should be highly available
• the service should be scalable
• the service should have fault tolerance

Capacity estimation

Assuming that the average size of the URLs are 200 character, and we will store 8 length character strings along with them.

The storage requirement will be around 210 character, which is 210 Bytes.

If we store 1000.000 URLs in a given time (e.g we delete the expired ones) then we will have 210 * 1000_000 / (1024 * 1024) mb requirement which is 0.2 GB storage.

The application will be read heavy, therefore database will have replicas for the read operations.

API design

POST - /url

body - param: long_url

response:

201 - CREATED - shortened url

403- Not authorized

401 - not authenticated

400 - bad request - invalid URL e.g

500 - internal server error

GET /url

requestParam - url - shortened URL

404 - not found

.... other response codes

Database design

table-name - urls

columns: long_url, short_url, created_at, last_access, expires_at, is_expired

High-level design

We will us layered architecture here, client will call backend APIs and the backend will call database.

There will be in memory cache before the database to return "hot" URLs.

Request flows

Client -> CDN

-> load-balancer -> backend -> cache -> database

Detailed component design

Trade offs/Tech choices

The frontend will be running via React, the backend will be running on java/spring-boot and the database will be PostGres.

Failure scenarios/bottlenecks

• rate limiting
• pick times
• hot urls

Future improvements

What are some future improvements you would make? How would you mitigate the failure scenario(s) you described above?