Configuration Providers

Configuration providers exist for settings files, environment variables, Azure key vault, Azure app configuration, command-line arguments, custom providers, key-per-file, and in-memory .NET objects.

Prefer Microsoft.Extensions.Configuration over System.Configuration.
Prefer Microsoft.Extensions.ConfigurationManager over System.ConfigurationManager.

Packages

• Microsoft.Extensions.Configuration
• Microsoft.Extensions.Hosting — Not required unless using a Generic Host.
• Microsoft.Extensions.Configuration.Binder — Bind an object to data in configuration providers.
• Microsoft.Extensions.Configuration.Json — JSON configuration provider.
• Microsoft.Extensions.Configuration.EnvironmentVariables — Environment variables provider.

Note: System.Configuration.ConfigurationBuilder != Microsoft.Extensions.Configuration.ConfigurationBuilder.

Binding

Configuration values can be bound to instances of .NET objects.

Interfaces:

• IConfiguration — Represents a set of key/value configuration properties.
• IConfigurationRoot — The root of an IConfiguration hierarchy.
• IConfigurationSection — A section of configuration values.

Configuration Provider Priority

1. Command Line
2. App Secrets (Secret Manager) in development environment
3. Environment Variables
4. XML / JSON / INI

This means #1 will override #2 and so on.

JSON Configuration Provider

using IHost host = Host.CreateDefaultBuilder(args).ConfigureAppConfiguration((hostingContext, configuration) =>
{
    // Clear all providers that were added from CreateDefaultBuilder():
    configuration.Sources.Clear();

    IHostEnvironment env = hostingContext.HostingEnvironment;

    // *Build Action* must be set to *Content*; *Copy to Output Directory* must be *Copy if newer* or *Always*.
    configuration
    .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
    .AddJsonFile($"appsettings.{env.EnvironmentName}.json", true, true);

    // Get the root of the configuration hierarchy. Sections from the configuration can be bound to .NET
    // objects and provided as IOptions<TOptions> through dependency injection.
    IConfigurationRoot configurationRoot = configuration.Build();

    // This class is for the options in appsettings.json:
    TransientFaultHandlingOptions options = new();
    configurationRoot.GetSection(nameof(TransientFaultHandlingOptions))
    .Bind(options);

    Console.WriteLine($"TransientFaultHandlingOptions.Enabled={options.Enabled}");
    Console.WriteLine($"TransientFaultHandlingOptions.AutoRetryDelay={options.AutoRetryDelay}");
})
.Build();

// Application code should start here.

await host.RunAsync();

Environment Variables Configuration Provider

Same code as above, except:

configuration.AddEnvironmentVariables();

Prefixes

// Set a prefix:
configuration.AddEnvironmentVariables(prefix: "CustomPrefix_");

Environment Variable Hierarchical Keys Separator

The : separator does not work with environment variable hierarchical keys on all platforms. Use __ instead. So, instead ofset TransientFaultHandlingOptions:Enabled="true" Use:set TransientFaultHandlingOptions__Enabled="true" Note: Use setx to persist the environment variable. Use setx /M to make it a system environment variable.

Command Line Arguments Configuration Provider

Same come as above, except:

if (args is { Length: > 0})
configuration.AddCommandLine(args);

Sending Command Line Arguments with dotnet

dotnet run *SomeKey*="*Some value*"

INI Configuration Provider

Same code as above, except:

configuration.AddIniFile(appsettings.ini", optional: true, reloadOnChange: true)

Memory Configuration Provider

using IHost host = Host.CreateDefaultBuilder(args).ConfigureAppConfiguration((_, configuration) =>
    configuration.AddInmemoryCollection(
        new Dictionary<string, string> {
        ["*SomeKey*"] = "*Some value*",
        ["*SomeOtherKey*:*Enabled*"] = bool.TrueString
    }))
.Build();

Additional Reading

Safe storage of app secrets in development in ASP.NET Core | Microsoft Docs