How to add an appsettings.json file to my Azure Function 3.0 configuration?

Question

The new Azure Function 3.0 SDK provides a way to implement a Startup class. It gives access to the collection of services that are available by dependency injection, where I

Answer 1

Nkosi's solution works pretty well, but it does update the way the azure function runtime loads settings for itself, by replacing IConfiguration singleton: services.AddSingleton.

I prefer having another IConfigurationRoot that is not injected. I just need to inject my settings IOption that are linked to my own IConfigurationRoot.

I build another IConfigurationRoot that is member of the Startup class:

public class Startup : FunctionsStartup
{
    private IConfigurationRoot _functionConfig = null;

    private IConfigurationRoot FunctionConfig( string appDir ) => 
        _functionConfig ??= new ConfigurationBuilder()
            .AddJsonFile(Path.Combine(appDir, "appsettings.json"), optional: true, reloadOnChange: true)
            .Build();

    public override void Configure(IFunctionsHostBuilder builder)
    {
         builder.Services.AddOptions()
             .Configure>((mlSettings, exeContext) =>
                 FunctionConfig(exeContext.Value.AppDirectory).GetSection("MachineLearningSettings").Bind(mlSettings) );
    }
}

Note: connection strings must remain in the application settings, because it is required by triggers to create an instance of the the function app that is not started (in a consumption service plan).