Change Kestrel port at runtime

Question

My project uses .net core 3.1 and is a web app using builtin server Kestrel.
I setup the ports using .UseUrls("http://0.0.0.0:1234") during CreateWebHostBuilder() and works as it should.

In my interface I wanted the user to able to change port at runtime.
But I have to restart the application with the new saved config to get that working.
Are there any tips on how to change it at runtime?

Answer 1

I solved (quick and dirty) the restart-server function for Kestrel.
This method is just a hack and should not be used in production. Maybe there are some clever heads out there who can make it better.

public class Program
{
    //Simple bool to tell the host to load again
    public static bool RestartWebserver { get; set; } = false;
    
    //Port to use
    public static int HttpPort { get; set; } = 80;

    //Main program
    public static int Main(string[] args)
    {
        //Infinityloop if 
        while(true)
        {
            CreateWebHostBuilder(args, Directory.GetCurrentDirectory()).Build().Run();
            
            //If RestartWebserver is false, exit everything...
            if (!RestartWebserver)
            {
                Console.WriteLine("Restarting...");
                break;
            }
            
            //Reset for the "new" host to be created.
            RestartWebserver = false;
        }
    }

    //Helper for creating host, returns a IWebHostBuilder to be Build and runned.
    public static IWebHostBuilder CreateWebHostBuilder(string[] args, string ContentRoot)
    {
        var Address = "0.0.0.0";
        string http = "http://" + Address + ":" + HttpPort;

        //Add arguments to the config (we could have a port set here too..)
        var configuration = new ConfigurationBuilder()
                .AddCommandLine(args)
                .Build();
        Startup.Configuration = configuration;

        //Return Webhost
        return WebHost.CreateDefaultBuilder(args)
            .UseStartup<Startup>()
            .UseContentRoot(ContentRoot)
            .UseKestrel()
            .UseUrls(new string[] { http }));
    }
}

//Now in any controller you can force close the host like this
public class RestartController : Controller
{
    public IHostApplicationLifetime _applicationLifetime;
    
    public StatusController(IHostApplicationLifetime applicationLifetime)
    {
        _applicationLifetime = applicationLifetime;
    }

    public async Task<IActionResult> Index()
    {
        //Set new port
        Program.HttpPort = 12345;
        
        //Set the server to restart
        Program.RestartWebserver = true;
        
        //Quit current host
        _applicationLifetime.StopApplication();

        //This function will fail.
        //Suggest to create a javascript file to reload client to the new port...
        return View("Index");
    }
}

This method worked for me, but the code above is kind of sudo, it has never been compiled in its form. Concept though is tested and confirmed on dotnet v5.0.100