appsettings does not get reloaded when using UseConfiguration extension method

[BennieCopeland]

The appsettings.json file is never reloaded on change when using the UseConfiguration extension method.

public static IWebHost DoesntWork(string[] args)
{
    var config = new ConfigurationBuilder()
        .SetBasePath(Directory.GetCurrentDirectory())
        .AddJsonFile("appSettings.json", optional: false, reloadOnChange: true)
        .Build();

    return new WebHostBuilder()
        .UseKestrel()
        .UseConfiguration(config)
        .UseContentRoot(Directory.GetCurrentDirectory())
        .UseIISIntegration()
        .UseStartup<Startup>()
        .Build();
}

Using the ConfigureAppConfiguration extension method however does cause the appsettings.json file to be reloaded on change.

public static IWebHost Works(string[] args)
{
    return new WebHostBuilder()
        .UseKestrel()
        .ConfigureAppConfiguration((builder, config) =>
        {
            config.AddJsonFile("appSettings.json", optional: false, reloadOnChange: true);
        })
        .UseContentRoot(Directory.GetCurrentDirectory())
        .UseIISIntegration()
        .UseStartup<Startup>()
        .Build();
}

I've created a sample project that uses a feature toggle to optionally print "Hello World" on the home page.
Example project: https://github.com/BennieCopeland/AppSettingBug

[Tratcher]

That's expected. UseConfiguration copies all of the keys:

Hosting/src/Microsoft.AspNetCore.Hosting.Abstractions/HostingAbstractionsWebHostBuilderExtensions.cs

Lines 24 to 32 in a63932a

	public static IWebHostBuilder UseConfiguration(this IWebHostBuilder hostBuilder, IConfiguration configuration)
	{
	foreach (var setting in configuration.AsEnumerable())
	{
	hostBuilder.UseSetting(setting.Key, setting.Value);
	}
	return hostBuilder;
	}

It would be nice to change this behavior in 3.0.

[BennieCopeland]

Is there documentation on the difference between host and application configuration? While I like the changes that took place with 2.0, it kind of muddied the waters when figuring out configuration. And this:

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

hides a lot of the magic. It's not clear on if I can override settings by just adding UseKestrel(options => {...}), so I went back to the long way of using WebHostBuilder and ran into my issue above.

It seems that there are now at least two configurations, a Host UseConfiguration and Application ConfigureAppConfiguration, which is fine, but the documentation could be clearer. The IOptionsSnapshot page talks about the hot reloading, but doesn't say how to enable it. The Configuration page, talks all about configuration, and file formats, and custom providers; but all the examples use the ConfigurationBuilder and don't show how it plugs into ASP.Net Core. The Hosting page talks about UserConfiguration, but ConfigureAppConfiguration isn't even documented. It shows up in a code example on the Startup page, but is never explained.

[Tratcher]

https://docs.microsoft.com/en-us/aspnet/core/fundamentals/host/web-host?view=aspnetcore-2.1&tabs=aspnetcore2x is the doc where this should go. Please comment there.

[Tratcher]

That is not related to hosting or this issue. Please open a new issue against configuration.

[Tratcher]

There's not a good way to fix UseConfiguration since it's an extension method on IWebHostBuilder which only has GetSetting and UseSetting and we're trying to avoid breaking the interface.

This isn't an issue going forward because generic host has ConfigureHostConfiguration with first class config support.