public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .UseUnityServiceProvider()   <---- Add this line
        .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.UseStartup<Startup>();
        });

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .UseUnityServiceProvider(_container)   //<---- Add this line
        .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.UseStartup<Startup>();
        });

public void ConfigureContainer(IUnityContainer container)
{
  // Could be used to register more types
  container.RegisterType<IMyService, MyService>();
}

public void ConfigureServices(IServiceCollection services)
{
    ...
    services.AddMvc()
        .AddControllersAsServices()  //<-- Add this line
        .SetCompatibilityVersion(CompatibilityVersion.Version_3_0)
    ...
}