Configure an ASP.NET Core app for Azure App Service

ASP.NET Core apps must be deployed to Azure App Service as compiled binaries. The Visual Studio publishing tool builds the solution and then deploys the compiled binaries directly. The App Service deployment engine deploys the code repository first and then compiles the binaries.

This guide provides key concepts and instructions for ASP.NET Core developers. If this is your first time using Azure App Service, first follow the ASP.NET Core quickstart and ASP.NET Core with SQL Database tutorial.

dotnet --info

az webapp config show --resource-group <resource-group-name> --name <app-name> --query linuxFxVersion

az webapp list-runtimes --os linux | grep DOTNET

Set .NET Core version

az webapp config set --name <app-name> --resource-group <resource-group-name> --linux-fx-version "DOTNETCORE|8.0"

What happens to outdated runtimes in App Service?

Outdated runtimes are deprecated by the maintaining organization or found to have significant vulnerabilities. Accordingly, they're removed from the create and configure pages in the portal. When an outdated runtime is hidden from the portal, any app that's still using that runtime continues to run.

If you want to create an app with an outdated runtime version that's no longer shown on the portal, use the Azure CLI, ARM template, or Bicep. These deployment alternatives let you create deprecated runtimes that have been removed in the portal, but are still being supported.

If a runtime is fully removed from the App Service platform, your Azure subscription owner receives an email notice before the removal.

az webapp config appsettings set --name <app-name> --resource-group <resource-group-name> --settings PRE_BUILD_COMMAND="echo foo, scripts/prebuild.sh"
az webapp config appsettings set --name <app-name> --resource-group <resource-group-name> --settings POST_BUILD_COMMAND="echo foo, scripts/postbuild.sh"

Access environment variables

In App Service, you can set app settings outside your app code. You can then access them in any class by using the standard ASP.NET Core dependency injection pattern:

using Microsoft.Extensions.Configuration;

namespace SomeNamespace 
{
    public class SomeClass
    {
        private IConfiguration _configuration;
    
        public SomeClass(IConfiguration configuration)
        {
            _configuration = configuration;
        }
    
        public SomeMethod()
        {
            // retrieve nested App Service app setting
            var myHierarchicalConfig = _configuration["My:Hierarchical:Config:Data"];
            // retrieve App Service connection string
            var myConnString = _configuration.GetConnectionString("MyDbConnection");
        }
    }
}

If you configure an app setting with the same name in App Service and in appsettings.json, for example, the App Service value takes precedence over the appsettings.json value. By using the local appsettings.json value, you can debug the app locally, but by using the App Service value, you can run the app in production with production settings. Connection strings work the same way. By using this method, you can keep your application secrets outside your code repository and access the appropriate values without changing your code.

az webapp config appsettings set --name <app-name> --resource-group <resource-group-name> --settings My__Hierarchical__Config__Data="some value"

az webapp config appsettings set --name <app-name> --resource-group <resource-group-name> --settings My:Hierarchical:Config:Data="some value"

Deploy multi-project solutions

When a Visual Studio solution includes multiple projects, the Visual Studio publish process automatically selects the project to deploy. When you deploy to the App Service deployment engine, such as with Git, or with ZIP deploy with build automation enabled, the App Service deployment engine picks the first website or web application project that it finds as the App Service app. You can specify which project App Service should use by specifying the PROJECT app setting. For example, run the following command in Cloud Shell:

az webapp config appsettings set --resource-group <resource-group-name> --name <app-name> --settings PROJECT="<project-name>/<project-name>.csproj"

Access diagnostic logs

ASP.NET Core offers a built-in logging provider for App Service. In your project's program.cs file, add the provider to your application through the ConfigureLogging extension method, as shown in the following example:

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .ConfigureLogging(logging =>
        {
            logging.AddAzureWebAppDiagnostics();
        })
        .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.UseStartup<Startup>();
        });

You can then configure and generate logs with the standard .NET Core pattern.

To access the console logs generated from inside your application code in App Service, turn on diagnostic logging by running the following command in Cloud Shell:

az webapp log config --resource-group <resource-group-name> --name <app-name> --docker-container-logging filesystem --level Verbose

Possible values for --level are Error, Warning, Info, and Verbose. Each subsequent level includes the previous level. For example, Error includes only error messages. Verbose includes all messages.

After you turn on diagnostic logging, run the following command to see the log stream:

az webapp log tail --resource-group <resource-group-name> --name <app-name>

If console logs don't appear immediately, check again in 30 seconds.

To stop log streaming at any time, select Ctrl+C.

For more information on troubleshooting ASP.NET Core apps in App Service, see Troubleshoot ASP.NET Core on Azure App Service and IIS.

Access a detailed exceptions page

When your ASP.NET Core app generates an exception in the Visual Studio debugger, the browser displays a detailed exception page, but in App Service that page is replaced by a generic "HTTP 500" or "An error occurred while processing your request." To display the detailed exception page in App Service, add the ASPNETCORE_ENVIRONMENT app setting to your app by running the following command in Cloud Shell.

az webapp config appsettings set --name <app-name> --resource-group <resource-group-name> --settings ASPNETCORE_ENVIRONMENT="Development"

Detect HTTPS session

In App Service, TLS/SSL termination happens at the network load balancers, so all HTTPS requests reach your app as unencrypted HTTP requests. If your app logic needs to know if user requests are encrypted, configure the Forwarded Headers Middleware in Startup.cs:

• Configure the middleware with ForwardedHeadersOptions to forward the X-Forwarded-For and X-Forwarded-Proto headers in Startup.ConfigureServices.
• Add private IP address ranges to the known networks, so that the middleware can trust the App Service load balancer.
• Invoke the UseForwardedHeaders method in Startup.Configure before calling other middleware.

When you assemble the three elements, your code looks like the following example:

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc();

    services.Configure<ForwardedHeadersOptions>(options =>
    {
        options.ForwardedHeaders =
            ForwardedHeaders.XForwardedFor | ForwardedHeaders.XForwardedProto;
        // These three subnets encapsulate the applicable Azure subnets. At the moment, it's not possible to narrow it down further.
        options.KnownNetworks.Add(new IPNetwork(IPAddress.Parse("::ffff:10.0.0.0"), 104));
        options.KnownNetworks.Add(new IPNetwork(IPAddress.Parse("::ffff:192.168.0.0"), 112));
        options.KnownNetworks.Add(new IPNetwork(IPAddress.Parse("::ffff:172.16.0.0"), 108));
    });
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app.UseForwardedHeaders();

    ...

    app.UseMvc();
}

For more information, see Configure ASP.NET Core to work with proxy servers and load balancers.

https://<app-name>.scm.azurewebsites.net/webssh/host

2019-04-08T14:07:56.641002476Z "-" - - [08/Apr/2019:14:07:56 +0000] "GET /robots933456.txt HTTP/1.1" 404 415 "-" "-"

Related content

• Tutorial: ASP.NET Core app with SQL Database

• Environment variables and app settings reference