using System;
using Microsoft.AspNetCore;
using Microsoft.AspNetCore.Hosting;

namespace TestService
{
    public class Service
    {
        IWebHost _webHost;

        public Service()
        {
            _webHost = WebHost.CreateDefaultBuilder()
                .UseStartup<Startup>()
                .Build();
        }

        public void Start()
        {
            _webHost.Start();
        }
    }
}

using System;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;

namespace TestService
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
        }

        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment()) {
                app.UseDeveloperExceptionPage();
            }

            app.UseMvc();
        }
    }
}

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Library</OutputType>
    <TargetFramework>netcoreapp2.2</TargetFramework>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore" Version="2.2.0"/>
    <PackageReference Include="Microsoft.AspNetCore.Mvc" Version="2.2.0"/>
  </ItemGroup>
</Project>

using System;

namespace TestService.Cli
{
    class Program
    {
        static void Main(string[] args)
        {
            var service = new Service();
            service.Start();
            Console.WriteLine("Hello World!");
            Console.ReadKey();
        }
    }
}