HttpClientFactory netstandard2.0

BackgroundThing.cs

using System;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Hosting;

namespace HttpClientEndpoint
{
    public class BackgroundThing : IHostedService, IDisposable
    {
        private readonly IHttpClientFactory _httpClientFactory;

        public BackgroundThing(
            IHttpClientFactory httpClientFactory
        ) {
            _httpClientFactory = httpClientFactory;
        }

        public void Dispose()
        {
        }

        public async Task StartAsync(CancellationToken cancellationToken)
        {
            Console.WriteLine("Starting connections");
            for(int i = 0; i<10; i++)
            {
                var client = _httpClientFactory.CreateClient("AspNetMonsters");

                var result = await client.GetAsync("");
                Console.WriteLine(result.StatusCode);
            }
            Console.WriteLine("Connections done");
        }

        public Task StopAsync(CancellationToken cancellationToken)
        {
            return Task.CompletedTask;
        }
    }
}

HttpClientEndpoint.csproj

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>netcoreapp2.0</TargetFramework>
    <LangVersion>7.1</LangVersion>
  </PropertyGroup>

  <ItemGroup>
    <Folder Include="wwwroot\" />
  </ItemGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.All" Version="2.0.5" />
    <PackageReference Include="Microsoft.Extensions.Http" Version="2.1.0-alpha-1" />
  </ItemGroup>

</Project>

Log from netstat

  TCP    172.26.215.21:59419    104.42.226.176:https   TIME_WAIT
  TCP    172.26.215.21:59420    waws-prod-bay-017:http  ESTABLISHED
  TCP    172.26.215.21:59421    waws-prod-bay-017:https  ESTABLISHED
  TCP    172.26.215.21:59423    ec2-54-159-86-114:https  ESTABLISHED
  TCP    172.26.215.21:59426    ec2-34-227-148-88:https  ESTABLISHED
  TCP    172.26.215.21:59565    sdcsrvfs01:microsoft-ds  ESTABLISHED

Program.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net.Http;
using System.Threading.Tasks;
using Microsoft.AspNetCore;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Logging;

namespace HttpClientEndpoint
{
    public class Program
    {
        public static void Main(string[] args)
        {
            BuildWebHost(args).Run();
        }

        public static IWebHost BuildWebHost(string[] args) =>
            WebHost.CreateDefaultBuilder(args)
                .UseStartup<Startup>()
                .Build();
    }
}

Startup.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

namespace HttpClientEndpoint
{
    public class Startup
    {
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddMvc();

            services.AddHttpClient("GitHubClient", client => {
                client.BaseAddress = new Uri("https://api.github.com/");
                client.DefaultRequestHeaders.Add("Accept", "application/vnd.github.v3+json");
                client.DefaultRequestHeaders.Add("User-Agent", "HttpClientFactoryTesting");
            });

            services.AddHttpClient("AspNetMonsters", client => {
                client.BaseAddress = new Uri("http://aspnetmonsters.com");
            });

            services.AddSingleton<IHostedService, BackgroundThing>();
        }

        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            } else
            {
                app.UseExceptionHandler("/Error");
            }

            app.UseMvcWithDefaultRoute();
        }
    }
}