Wrong configuration injected into Startup

[BalassaMarton]

Try this setup:

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

        public static IConfiguration BuildConfiguration()
        {
            return new ConfigurationBuilder()
                .SetBasePath(Directory.GetCurrentDirectory())
                .AddJsonFile("appsettings.json")
                .AddJsonFile("othersettings.json")
                .Build();
        }

        public static IWebHostBuilder CreateWebHostBuilder(string[] args)
        {
            return WebHost.CreateDefaultBuilder(args)
                .UseConfiguration(BuildConfiguration())
                .UseStartup<Startup>();
        }
    }

    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // ...  
    }

The configuration object injected into Startup will not have any values or providers from the one passed to UseConfiguration, e.g. nothing from othersettings.json. The configuration is otherwise correctly injected into controllers and pages.

[BalassaMarton]

Workaround is to use ConfigureAppConfiguration instead of UseConfiguration.

[khellang]

It's not really a "workaround". Everything works as designed, as confusing as it is. The ConfigureAppConfiguration exist for a reason 😉 See https://github.com/aspnet/Hosting/issues/1148#issuecomment-318524939

[BalassaMarton]

From documentation:

Host configuration key-value pairs become part of the app's global configuration.

And from another documentation page:

IWebHostBuilder configuration is added to the app's configuration, but the converse isn't true—ConfigureAppConfiguration doesn't affect the IWebHostBuilder configuration.

While it is true that the application isn't really running yet when Startup methods are called, this is very couter-intuitive.

But the disturbing thing is that I can't even repro it on my home machine, like it was some SDK-specific thing. Here Startup receives host+app configuration as expected. I need to check this again on my work machine.

[BalassaMarton]

After a few hours of trial and error, I can finally repro the problem. It's not that the wrong instance is injected. When using WebHost.CreateDefaultBuilder, appsettings.json is loaded after anything that was passed to UseConfiguration, overwriting existing values. The problem goes away when either calling ConfigureAppConfiguration or building the host manually with a new WebHostBuilder. I'm not sure if this qualifies as a bug, it's more like a documentation problem. The previously quoted sections fail to mention that the default builder itself calls ConfigureAppConfiguration, which ultimately overwrites anything passed in UseConfiguration. To try it out, clone this repo and fiddle with the switches in Program.cs https://github.com/BalassaMarton/AspnetHosting1528Repro

[lonix1]

This is certainly a mess!

In my case I need to start logging before the webhost, to ensure if something goes wrong during startup, it gets logged! So I setup 1) configuration, 2) logging (serilog) and 3) webhost.

So obviously I pass the config into UseConfiguration() and it doesn't work properly. But if I use ConfigureAppConfiguration() it does work, but trashes the existing config, so my webhost and logging are using different config!

@BalassaMarton What approach are you now using?

[khellang]

@lonix1 Sounds like https://github.com/aspnet/Hosting/issues/1150

[lonix1]

I posted a separate issue for that.

@BalassaMarton I tried your code and get the same results.

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