ConfigureWebHost() is not supported by WebApplicationBuilder.Host. Use the WebApplication returned by WebApplicationBuilder.Build() instead" error

Question

I have just upgraded a dotnet core 3 api application to a 6.

So before, I had a startup.cs file with a ConfigureServices and a Configure method.

In order to not accidently break anything, and also perhaps save myself from doing work, I wanted to keep the startup.cs file.

So where I before used createdefaultbuilder, like this:

    public static void Main(string[] args)
    {
        CreateHostBuilder(args).Build().Run();
    }

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

But now, I need to call "createBuilder" instead, and now my program.cs looks like this, where I try to use startup.cs by calling "ConfigureWebHostDefaults" on the host instead.

    public static void Main(string[] args)
    {
        CreateHostBuilder(args).Build().Run();
    }

    public static WebApplicationBuilder CreateHostBuilder(string[] args)
    {
        var webApplicationOptions = new WebApplicationOptions() { ContentRootPath = AppContext.BaseDirectory, Args = args, ApplicationName = System.Diagnostics.Process.GetCurrentProcess().ProcessName };
        var builder = WebApplication.CreateBuilder(webApplicationOptions);
        
        builder.Host.ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.UseStartup<Startup>();
        });
        builder.Host.UseWindowsService();

        return builder;
    }

However, when I try to build and run, the "ConfigureWebHostDefaults", this error comes back at me:

ConfigureWebHost() is not supported by WebApplicationBuilder.Host. Use the WebApplication returned by WebApplicationBuilder.Build() instead.'

Which seems like a pretty obvious instruciton, I just need to call "ConfigureWebHostsDefaults" on the built "WebApplicationBuilder".

But "WebApplication" has no definition for anything called "ConfigureWebHostDefaults", "Usestartup" or a field called "Host"

So it's entirely unclear to me what the error is trying to tell me.

Can someone help me out?

Answer 1

In case you are trying to configure Kestrel in ConfigureWebHostDefaults, it can be done through builder.WebHost.ConfigureKestrel instead, this won't throw an error:

builder.WebHost.ConfigureKestrel(serverOptions =>
{
   serverOptions.Listen(System.Net.IPAddress.Any, 44380, listenOptions =>
   {
       listenOptions.Protocols = HttpProtocols.Http1AndHttp2;
       listenOptions.UseHttps("self.pfx", "123qwe");
   });
});