Controller's action not invoked in ASPNETCORE console app running Kestrel - asp.net-core

Question

I'd like to have a console application running a standalone webserver accepting REST calls. My application is a .NET Core app with ASP .NET Core inside. I am completely new in this area. I found some examples and now I am struggling with controller route configuration. With the code below I always get "404 Not Found" error when using http://localhost:3354/api/Demo/Hello. Does anyone have an idea what am I doing wrong? Thank you for any suggestion!
I use VS2019 and ASPNETCORE 2.2.8.
class Program
{
static void Main(string[] args)
{
var builder = WebHost.CreateDefaultBuilder()
.ConfigureKestrel(options => options.ListenAnyIP(3354))
.UseStartup<Startup>();
builder.Build().Run();
}
}
public class Startup
{
public void ConfigureServices(IServiceCollection services)
{
services.AddMvc();
}
public void Configure(IApplicationBuilder builder, IHostingEnvironment env)
{
builder.UseMvc(delegate(IRouteBuilder routeBuilder)
{
routeBuilder.MapRoute("default", "api/{controller}/{action}");
});
}
}
Here comes the DemoController class.
public class DemoController : Controller
{
public IActionResult Hello()
{
return Ok("Hello world");
}
}

Answer 1

Your example is working fine for me on .net core 2.2
You could try explicitly declare routes like
[ApiController]
[Route("api/[controller]")]
public class DemoController : Controller
{
[HttpGet("hello")]
public IActionResult Hello()
{
return Ok("Hello world");
}
}
Also you could consider using Visual studio built-in templates of api web applications

Answer 2

After some investigation and comparison of my project with the sample project of Roman Kalinchuk I found out that the problem is that mvc controller provider doesn't look for controller types in my application assembly. It is enought to add my application assembly to the application parts collection.
See the .AddApplicationPart(typeof(DemoController).Assembly); line.
public class Startup
{
public void ConfigureServices(IServiceCollection services)
{
services
.AddMvc()
.AddApplicationPart(typeof(DemoController).Assembly);
}
public void Configure(IApplicationBuilder builder, IHostingEnvironment env)
{
env.EnvironmentName = "Development";
builder.UseMvc(delegate(IRouteBuilder routeBuilder)
{
routeBuilder.MapRoute("test", "api/{controller}/{action}");
});
}
}