After updating a .NET Core 2.2 app to NET 5, the following error appeared:

System.InvalidOperationException: ‘Application is running inside IIS process but is not configured to use IIS server.’

To fix this use HotBuilder instead of WebHostBuilder

public class Program

{


    private static readonly log4net.ILog log = log4net.LogManager.GetLogger(typeof(Program));

    public static void Main(string[] args)


    {


        CreateHostBuilder(args).Build().Run();


    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>


        Host.CreateDefaultBuilder(args)


            .ConfigureWebHostDefaults(webBuilder =>


            {


                webBuilder


                .UseKestrel(serverOptions => serverOptions.AddServerHeader = false)


                .UseIISIntegration()


                .UseStartup<Startup>();


            });


}