Azure web app with .NET Core 3.0 fails: Can't find Microsoft.AspNetCore.App

We had exactly the same problem. Azure App Service does not currently support Net Core 3.

The temporary workaround is to build a self contained app from Visual Studio through the publish tool. You can change it from Framework Dependent to Self Contained in the publishing settings. Simply deploy that to Azure.

We also tried to use our DevOps pipelines to do this, but couldn't work out how to do a self contained build and as Azure will hopefully support Net Core 3 soon, the publish works fine for now.

Hope that helps :)

You can keep track on the latest releases on the ASP.NET Core on App Service Dashboard

You can add .net core 3.0 x86/ 64 framework using Azure app service extension (open app service -> extensions). Then publish .net core 3.0 app.