Requirements

Functional Requirements:

• As a creator, I can create a short URL for a given long URL.
• As a creator, I can delete a previously created URL
• As a consumer, automatically redirect me to the long URL
• Functional requirements not included here:
  • Ability for creators to edit their link
  • Ability for creators to see insights on their link (number of visits for instance)
  • Ability for creators to put a long URL based on the geography (or any other property from the client browser)
  • Ability for creators to pick the name of the URL

Non-Functional Requirements:

• High availability as the availability of the ultimate page is the combination of the shortener URL service and the long URL too
• Very low latency as you don't want
• High scalability as some links can receive a lot of viewers
• High short link variance as you don't want to have a short url collision
• Eventual consistency: it's fine for links to take multiple minutes/seconds to be created/deleted
• There must be an authentication/authorization system in place so creators can delete their links

API Design

• POST /manage
  • Request headers:
    • OAuth2 Bearer token in authorization header
  • Request body:
    • { "longUrl": "{longUrl}" }
  • Response body:
    • { "id": "{createdId}" }
• DELETE /manage/{shortURL}
  • Request headers:
    • OAuth2 Bearer token in authorization header
  • Response: 200
• GET /{shortUrl}
  • Response: 301 Moved Permanently

High-Level Design

Use client-side browser caching as much as possible by returning a 301 Moved Permanently along with the appropriate Cache control headers so that for a given client, there is no further complete GET request on our side.

It's a low-write, heavy-read situation so we can use a SQL database to store the mapping between short and long URL acting as a source of truth.

We have two services:

• Link Management service, in the control plane to add/delete links
• Link Redirection service, in the data plane to get links and redirect users

We're always sending the same response so we could put a CDN in front

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.