Clarify env var config in Azure Apps topic (dotnet#16225)

Author: guardrex

aspnetcore/host-and-deploy/azure-apps/index.md

@@ -5,7 +5,7 @@ description: This article contains links to Azure host and deploy resources.
 monikerRange: '>= aspnetcore-2.1'
 ms.author: bradyg
 ms.custom: mvc
-ms.date: 11/07/2019
+ms.date: 12/16/2019
 uid: host-and-deploy/azure-apps/index
 ---
 # Deploy ASP.NET Core apps to Azure App Service
@@ -81,13 +81,13 @@ When an app setting is created or modified in the Azure Portal and the **Save**
 
 ::: moniker range=">= aspnetcore-3.0"
 
-When an app uses the [Generic Host](xref:fundamentals/host/generic-host), environment variables aren't loaded into an app's configuration by default and the configuration provider must be added by the developer. The developer determines the environment variable prefix when the configuration provider is added. For more information, see <xref:fundamentals/host/generic-host> and the [Environment Variables Configuration Provider](xref:fundamentals/configuration/index#environment-variables-configuration-provider).
+When an app uses the [Generic Host](xref:fundamentals/host/generic-host), environment variables are loaded into the app's configuration when <xref:Microsoft.Extensions.Hosting.Host.CreateDefaultBuilder*> is called to build the host. For more information, see <xref:fundamentals/host/generic-host> and the [Environment Variables Configuration Provider](xref:fundamentals/configuration/index#environment-variables-configuration-provider).
 
 ::: moniker-end
 
 ::: moniker range="< aspnetcore-3.0"
 
-When an app builds the host using [WebHost.CreateDefaultBuilder](/dotnet/api/microsoft.aspnetcore.webhost.createdefaultbuilder), environment variables that configure the host use the `ASPNETCORE_` prefix. For more information, see <xref:fundamentals/host/web-host> and the [Environment Variables Configuration Provider](xref:fundamentals/configuration/index#environment-variables-configuration-provider).
+When an app uses the [Web Host](xref:fundamentals/host/web-host), environment variables are loaded into the app's configuration when <xref:Microsoft.AspNetCore.WebHost.CreateDefaultBuilder*> is called to build the host. For more information, see <xref:fundamentals/host/web-host> and the [Environment Variables Configuration Provider](xref:fundamentals/configuration/index#environment-variables-configuration-provider).
 
 ::: moniker-end
 
@@ -140,14 +140,16 @@ When swapping between deployment slots, any system using data protection won't b
 For more information, see <xref:security/data-protection/implementation/key-storage-providers>.
 <a name="deploy-aspnet-core-preview-release-to-azure-app-service"></a>
 
-## Deploy ASP.NET Core 3.0 to Azure App Service
+## Deploy an ASP.NET Core app that uses a .NET Core preview
 
-ASP.NET Core 3.0 is supported on Azure App Service. To deploy a preview release of a .NET Core version later than .NET Core 3.0, use one of the following techniques. These approaches are also used when the runtime is available but the SDK hasn't been installed on Azure App Service.
+To deploy an app that uses a preview release of .NET Core, see the following resources. These approaches are also used when the runtime is available but the SDK hasn't been installed on Azure App Service.
 
 * [Specify the .NET Core SDK Version using Azure Pipelines](#specify-the-net-core-sdk-version-using-azure-pipelines)
-* [Deploy a self-contained preview app](#deploy-a-self-contained-preview-app).
-* [Use Docker with Web Apps for containers](#use-docker-with-web-apps-for-containers).
-* [Install the preview site extension](#install-the-preview-site-extension).
+* [Deploy a self-contained preview app](#deploy-a-self-contained-preview-app)
+* [Use Docker with Web Apps for containers](#use-docker-with-web-apps-for-containers)
+* [Install the preview site extension](#install-the-preview-site-extension)
+
+See the [ASP.NET Core on App Service Dashboard](https://aspnetcoreon.azurewebsites.net/) for the version of ASP.NET Core available on Azure App service.
 
 ### Specify the .NET Core SDK Version using Azure Pipelines