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Whiteboard: Real Time Collaboration using Azure SignalR Service

This is a sample project to demonstrate how to build a web application for real time collaboration using Azure, ASP.NET Core and other related technologies. This sample application includes the following features:

  • A whiteboard that anyone can paint on it and others can see you painting in real time
  • Painting features:
    1. Basic paint tools (freehand, line, rectangle, circle, ellipse), color and stroke thickness
    2. Upload a background image
    3. Pan and zoom canvas
    4. Undo and redo
    5. Touch support for mobile devices
  • Real time chat

This application is based on the following technologies:

  • For frontend: HTML5/javascript, bootstrap and vue.js
  • For backend: ASP.NET Core (for SignalR version), or node.js + express.js (for websocket version)
  • For realtime communication: WebSocket, SignalR and Azure SignalR Service

Build and run locally

SignalR version

This application has two versions, the SignalR version is built on top of ASP.NET Core SignalR and Azure SignalR Service. You can build and run it as a normal ASP.NET Core application:

  1. Create an Azure SignalR Service instance

  2. Get connection string

  3. Build and run the application locally

    dotnet build
dotnet user-secrets set Azure:SignalR:ConnectionString "<your connection string>"
dotnet run

Open multiple windows on http://localhost:5000/, when you paint in one window, others will see the update immediately.

You can also run it without Azure SignalR Service (Azure SignalR Service is used mainly for scalability considerations). To remove Azure SignalR Service dependency:

  1. Open Startup.cs, in ConfigureServices() change 
    services.AddSignalR().AddAzureSignalR();
    to 
    services.AddSignalR();
  2. [Optional] Remove the corresponding Azure SignalR dependency from Whiteboard.csproj.

WebSocket version

If you're not familiar with SignalR or cannot use this technology for some reason, you can still build the same application as long as you're familiar with WebSocket technology. WebSocket version shows to how to do that in WebSocket.

This version is based on an experimental feature in Azure SignalR Service called serverless WebSocket which allows you to build WebSocket applications in a serverless fashion. Basically Azure SignalR Service converts WebSocket connections into HTTP requests (WebHook) so you don't need to maintain WebSocket connections in your severless application (which is usually not possible in serverless world).

To build and run it locally:

  1. Get a connection string to Azure SignalR Service and set it as environment variable:

    set Azure__SignalR__ConnectionString=<your connection string>

  2. Then run the application:

    npm install
npm start

  3. Now you need a public accessible endpoint so that Azure SignalR Service can invoke you. We can use ngrok to achieve it. Install ngrok and use the following command to start it:

    ngrok http 8080

    Now you can see a public endpoint created by ngrok (something like https://abc.ngrok.io), set corresponding upstream urls in Azure SignalR Service.

    This feature is still in private preview. Check out this repo for more information about this feature and how to get private preview access.

Now your application will be available at: http://localhost:8080

Deploy to Azure

To deploy the application to Azure Web App, first package it into a zip file:

  • For SignalR version: 
    dotnet build
dotnet publish -c Release
    Then package all files under bin/Release/netcoreapp3.1/publish to a zip file.
  • For WebSocket version, just run npm install and then package all files into a zip file.

Then use the following command to deploy it to Azure Web App:

az webapp deployment source config-zip --src <path_to_zip_file> -n <app_name> -g <resource_group_name>

Don't forget to set Azure SignalR Service connection string in the application settings. You can do it through portal or using Azure CLI:

az webapp config appsettings set --resource-group <resource_group_name> --name <app_name> \
   --setting Azure__SignalR__ConnectionString="<connection_string>"

Also update corresponding upstream urls if you're using WebSocket version.

Now your whiteboard is running in Azure at https://<app_name>.azurewebsites.net. Enjoy!