Requirements

Functional Requirements:

• Able to register a URL to a URL shortner
• Map shortened url to be long url
• Handle the unique creation of the shortened url

Non-Functional Requirements:

• High availability
  • Uptime should be 99.999%
• Eventual consistency
  • Writes/Updates are infrequent, so I shouldn't lead to blocking access
• High scalability
  • Needs to be replicated globally

API Design

• POST /url/{long_url}
  • registers long_url
  • return 201 with shortened url

• GET /url/{short_url}
  • redirect to shortened url
  • returns 301
  • must be able to save metadata for later use

High-Level Design

From Client

Client -> Load Balancer -> API Layer -> Cache Layer -> DB Layer

• Client
  • Web Browser
• Load Balancer
  • Must redirect to the closest or most available cluster
• Cache: Caching Layer
  • Redis takes advantage of geo-replications
  • Write Policy: Write Through
  • Read Policy: Hit then Cache
• UrlShortenerServer: API Layer
  • Registers
    • Check long url existence
    • Create a shorten url to map with the long url
    • Write to the database
    • Write to cache
  • Get and Redirect
    • Check the cache then the database
    • Update metadata
    • Redirect
• Database: Storage Layer

Detailed Component Design

• Caching layer:
  • Significantly reduce latency when interacting with DB
  • Takes advantage of georeplication, which also leads to eventual consistency
  • The client initially attempts to retrieve a hit in the cache layer; if not found, it checks the database and then writes to the cache.
• URL Shortener Algorithm
  • Used in the API Layer when shortening long urls
  • Patterns we can use:
    • GUIDs
      • Is there shortened GUIDs
    • [aA-zZ]{0:8} leads to 26^8 if we need more add a new letter. Issue since it's incrementally easy to find the next available url.