A few weeks ago when the post Deploy ASP.NET Core 3 Previews to Azure App Service I got an email from Jerrie Pelser who pointed out that there are extensions available for App Service that allow usage of the public previews of ASP.NET Core 3 without having to do a self-contained deployment.

In addition to Jerrie’s suggestion pajaybasu pointed out in this Reddit post that using Docker is another option. Pajaybasu also pointed out a line in the original post where I that self-contained deployments were the only option which of course was incorrect.

The first half of this post is going to be the same as the original post which covers the creation and the initial publication to Azure App Service. The last half will cover using an extension to enable the preview version of ASP.NET Core.

Sample Application

I used the following .NET CLI command to create a new ASP.NET Core application using React for its front end.

dotnet new react

After the creation process is complete open the project in Visual Studio. I highly recommend using the Visual Studio 2019 preview release when working with any .NET Core 3 applications.

Publish to App Service

In Visual Studio’s Solution Explorer right click on the project file and select Publish.

Select App Service for the publish target. Here we are creating a new app service. Next, click Publish.

The next dialog if the information about the new App Service that will be created. I took the defaults for the most part. I did create a new resource group for this application to make the resources easier to clean up in the future. I also changed the hosting plan to the free tier. Click Create to continue.

The Error and the Warning

As part of the publishing process, a browser will be opened to the address of the application. When this happens you will see an error about ANCM In-Process Handler Load Failure (if you are using IIS In-Process Hosting).

If you look back at Visual Studio you will see the following warning that your application requires the .NET Core runtime 3.0 and App Service only supports up to 2.2. Since we are going to fix this in App Service I recommend selecting Don’t perform check in the future (only this profile).

Another Fix

For this version of the fix, go to your App Service in the Azure Portal. In the menu under the Development Tools select the Extensions option.

On the next page click the Add button at the top. Click on the Choose Extension and select the ASP.NET Core 3.0 (x86) Runtime option.

Next, click Legal Terms, read the terms and if you are OK with the terms then click the OK button. You will then have to click OK on the add extension blade which will start the extension installation.

If you were to load your site at this point you would still get the 500 error. Under Settings click the Configuration and click on General settings turn Web sockets On and click Save.

At this point, your site should be working. You can also go back and turn web sockets back off and the site will continue working. I have no idea what toggling web sockets does to make everything start working, but thanks to this comment on a GitHub issue for the key to getting this working.

Wrapping Up

Hopefully, between this post and the previous one using a self-contained deployment, you won’t have any issues trying out the .NET Core 3 with App Service.