Configuring Application Configuration in ASP.NET Core 2

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

        public static IWebHost BuildWebHost(string[] args) =>
            WebHost.CreateDefaultBuilder(args)
            .ConfigureAppConfiguration((ctx, cfgBuilder) =>
            {
                cfgBuilder.
                 AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
                .AddJsonFile($"appsettings.{ctx.HostingEnvironment.EnvironmentName}.json", 
                 optional: true)
                .AddEnvironmentVariables();
            })
                .UseStartup<Startup>()
                .Build();
    }