appsettings.json (both dev and prod) ignored by ASP.NET Core 2.0?

Looks like you need to call UseConfiguration directly to set an URL address read from appsettings.json:

public static IWebHost BuildWebHost(string[] args){        var config = new ConfigurationBuilder()            .AddJsonFile($"appsettings.Development.json", optional: true)            .Build();        return WebHost.CreateDefaultBuilder(args)            .UseConfiguration(config)            .UseStartup<Startup>()            .Build();}

CreateDefaultBuilder method implementation uses ConfigureAppConfiguration method internally, not UseConfiguration. And there is a difference (from related Github issue):

The ConfigureAppConfiguration was intended to configure the IConfiguration in the application services whereas UseConfiguration is intended to configure the settings of the WebHostBuilder. Since the url address is a setting on the WebHostBuilder only UseConfiguration will work here.

Note that the WebHostBuilder's configuration is added to the application's configuration but the converse is not true; configuring the application's configuration does not affect the WebHostBuilder's configuration.

Instread of "Kestel.Endpoints" section your appsetting.json should simply have the following:

{   ...   "urls": "http://127.0.0.1:5001"}