Creating a project

mkdir TestAspNetCoreHost
cd TestAspNetCoreHost
dotnet new web --no-https

Adding the NuGet packages

# For the main FTP server
dotnet add package FubarDev.FtpServer

# For the System.IO-based file system access
dotnet add package FubarDev.FtpServer.FileSystem.DotNet

Create an IHostedService implementation

Important

This is only required for version 3.0, because the FTP server will provide a much tighter ASP.NET Core integration in a future release.

Create a new file named HostedFtpService.cs, which contains the following code:

using System.Threading;
using System.Threading.Tasks;
using FubarDev.FtpServer;
using Microsoft.Extensions.Hosting;

namespace TestAspNetCoreHost
{
    internal class HostedFtpService : IHostedService
    {
        private readonly IFtpServerHost _ftpServerHost;

        /// <summary>
        /// Initializes a new instance of the <see cref="HostedFtpService"/> class.
        /// </summary>
        /// <param name="ftpServerHost">The FTP server host that gets wrapped as a hosted service.</param>
        public HostedFtpService(
            IFtpServerHost ftpServerHost)
        {
            _ftpServerHost = ftpServerHost;
        }

        /// <inheritdoc />
        public Task StartAsync(CancellationToken cancellationToken)
        {
            return _ftpServerHost.StartAsync(cancellationToken);
        }

        /// <inheritdoc />
        public Task StopAsync(CancellationToken cancellationToken)
        {
            return _ftpServerHost.StopAsync(cancellationToken);
        }
    }
}

Using the FTP server

Change your Program.cs to the following code:

using System.IO;
using FubarDev.FtpServer;
using FubarDev.FtpServer.FileSystem.DotNet;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

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

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
               .ConfigureServices(
                    services =>
                    {
                        // Add FTP server services
                        // DotNetFileSystemProvider = Use the .NET file system functionality
                        // AnonymousMembershipProvider = allow only anonymous logins
                        services
                           .AddFtpServer(
                                builder => builder
                                   .UseDotNetFileSystem()
                                   .EnableAnonymousAuthentication());

                        // Configure the FTP server
                        services.Configure<FtpServerOptions>(opt => opt.ServerAddress = "*");

                        // use %TEMP%/TestFtpServer as root folder
                        services.Configure<DotNetFileSystemOptions>(opt => opt
                            .RootPath = Path.Combine(Path.GetTempPath(), "TestFtpServer"));

                        // Add the FTP server as hosted service
                        services
                           .AddHostedService<HostedFtpService>();
                    })
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
    }
}

Starting the FTP server

dotnet run

Now your FTP server should be accessible at 127.0.0.1:21.