Introduction

This is your basic Url Shortening service similar to bit.ly. It can take long Url and convert to a short alias. Also, inflate short URL back to it's original form.

How it works

Short code generation

1. Compute MD5 hash of the given long Url
2. Convert MD5 to a base62 encoding ( a-z,A-Z,0-9)
3. Take first 6 characters as Short Url Code. In case of duplication, algorighthm takes the next 6 characters from base62 string untill all options are exhausted.

With base62 encoding six characters would produce 62^6 (56.8 Billion) possible Short codes which should suffice for this service.

User Interface

Service works in two modes: Public (default) and User(with User authentication).

Public mode

Anonymous Users can generated short urls without authentication. If user tries to generate a Short Url for a long Url that has already been converted, user will receive existing Short Code.

User mode

It is similar with public mode in terms of functionlity but requires authentications. Auth0 is used as an Identity provider. Users can see a list of all the URLs they converted on a separate page. If users tries to a Short Url for a long Url that has already been converted, user will receive existing Short Code.

Note: If a registered user tries to shorten a URL that has already been converted by a Anonymous user and not yet shortened by registered user, it will generate a new Short code.

Data Partiotioning

Azure Table Storage is used as a backend data store. To optimized the data retrival for redirect and User interface, data is stored in two tables.

UrlRead

Data in this table is consumed by URL shortening user interface. UserId is used as PartitionKey and 6 character Short Url Code is used as RowKey. This optimizes the URL data retrieval for Url List Page.

UrlRedirect

Date in this table is consumed by URL redirect module. First three characters of Shor Url Code are used as PartitionKey and 6 character Short Url Code is used as RowKey. This optimized the retrieval of Long url from short code while doing redirect.

Scaling

Both UI and redirector scale out if Average CPU% goes over 70%. Max scale count is 10, min is 1.

Caching

Url short code and long URL are stored as a Key/Value pair in Azure Cache for Redis for 7 days before they expire.

Data Replication

Azure storage account is Read-Access-Geo-Redundant Storage(RA-GRS) which provides geo-redundant storage with additional benefits of read accesss to the secondary endpoint. If an outage occurs in the primary endpoint, applications configured for RA-GRS and designed for high availability can continue to read from the secondary endpoint.

Project Structure

UrlShortener.Extensions

This project contains extensions methods for Base conversion and Md5 hash.

UrlShortener.Models

Contains all the Data Entities used by services and repositories.

UrlShortener.Redirector

This project handles the redirect from Short URL to long URL. It's deployed as a separate webapp so that it can be individually scaled as need arise.

UrlShortener.Repositories

Handles data store and retrieval from Azure Storage.

UrlShortener.Services

Contains all the business login and is unit tested.

UrlShortener.UI

It's the user interface for generating short urls.

UrlShortener.UnitTests

Has all the unit tests for business logic.

Run Locally

1. Checkout the repo locally
2. Open UrlShortener.sln in Visual Studio
3. Set UrlShortener.Redirector and UrlShortener.UI as startup projects. You can do this by going into properties of the solutions and select those two projects as startup projects.
4. Update ShortUrlDomain and UiDomain in appsettings.json of UrlShortener.Redirector and UrlShortener.UI with local host and port if required.

Live Version

UI - https://naniurl.azurewebsites.net Redirector- http://naniurl.club

PS: Nani means short in a local lanaguage from where I come.

Future

• API Access to developers
• Protection against abuse
• Infrastructure as code
• Use CosmosDb for high avaibility and lower latency if cost is not an issue.
• Do proper paging with Azure Storage