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

After some research, I came across this thread on Githib

using appsettings.json + IConfiguration in Function App

From which I crafted the following extension based on the comments and suggestions that showed to have worked.

public static class FunctionHostBuilderExtensions {
    /// 

    /// Set up the configuration for the builder itself. This replaces the 
    /// currently registered configuration with additional custom configuration.
    /// This can be called multiple times and the results will be additive.
    /// 
    public static IFunctionsHostBuilder ConfigureHostConfiguration (
        this IFunctionsHostBuilder builder, 
        Action configureDelegate) {
        IServiceCollection services = builder.Services;            
        var providers = new List();            
        //Cache all current configuration provider
        foreach (var descriptor in services.Where(d => d.ServiceType == typeof(IConfiguration)).ToList()) {
            var existingConfiguration = descriptor.ImplementationInstance as IConfigurationRoot;
            if (existingConfiguration is null) {
                continue;
            }
            providers.AddRange(existingConfiguration.Providers);
            services.Remove(descriptor);
        }
        //add new configuration based on original and newly added configuration
        services.AddSingleton(sp => {
            var configurationBuilder = new ConfigurationBuilder();                    
            //call custom configuration
            configureDelegate?.Invoke(sp, configurationBuilder);                
            providers.AddRange(configurationBuilder.Build().Providers);                
            return new ConfigurationRoot(providers);
        });            
        return builder;
    }
}

The main idea is to extract all the currently registered configuration related types, create a new builder, apply custom configuration and build a new configuration with the original and custom configuration details merged into one.

It would then be used in Startup

public class Startup : FunctionsStartup {
    public override void Configure(IFunctionsHostBuilder builder) {
        builder.ConfigureHostConfiguration((sp, config) => {
            var executioncontextoptions = sp.GetService>().Value;
            var currentDirectory = executioncontextoptions.AppDirectory;

            config
                .SetBasePath(currentDirectory)
                .AddJsonFile("appSettings.json", optional: true, reloadOnChange: true)
                .AddEnvironmentVariables();

            //if there are multiple settings files, consider extracting the list,
            //enumerating it and adding them to the configuration builder.
        });

        builder.Services
            .AddOptions()
            .Configure((settings, configuration) => {
                configuration.GetSection("MachineLearningConfig").Bind(settings);
            });
    }
}

The above should now be able to get the settings from your custom configuration.