C# (.NET) Application Configuration: Microsoft.Extensions.Configuration

C# (.NET) Application Configuration: A Complete Guide

Configuration management is one of the key tasks when developing modern applications in C# (.NET). The Microsoft.Extensions.Configuration library provides a powerful and flexible mechanism for reading settings from various sources: JSON files, environment variables, command-line arguments, and secrets. In this article, we will thoroughly examine how to configure .NET applications using best practices and code examples.

Key Features of the Library

• Multiple data sources: JSON, XML, INI, environment variables, command-line arguments, Azure Key Vault, and others.
• Hierarchical structure: support for nested sections using colon-separated keys (Section:Subsection:Key).
• Binding to classes (Options Pattern): automatic population of POCO objects from configuration.
• Flexible overriding: the last added source has the highest priority.
• Secrets support: Secret Manager for development, secure storage for production.

Installation and Setup

To work with configuration in a .NET application (console, ASP.NET Core, MAUI, etc.), you need to install the NuGet package:

dotnet add package Microsoft.Extensions.Configurationdotnet add package Microsoft.Extensions.Configuration.Jsondotnet add package Microsoft.Extensions.Configuration.EnvironmentVariablesdotnet add package Microsoft.Extensions.Configuration.CommandLine

In ASP.NET Core, these packages are already included by default.

Basic Example: Reading from appsettings.json

Create a file appsettings.json:

{  "Logging": {    "LogLevel": {      "Default": "Information",      "Microsoft": "Warning"    }  },  "ConnectionStrings": {    "DefaultConnection": "Server=localhost;Database=MyDb;User Id=sa;Password=MyPass;"  },  "AppSettings": {    "AppName": "MyApp",    "Version": "1.0.0",    "MaxRetries": 3  }}

Code for reading configuration in a console application:

using Microsoft.Extensions.Configuration;

class Program{    static void Main(string[] args)    {        // Create configuration        var configuration = new ConfigurationBuilder()            .SetBasePath(Directory.GetCurrentDirectory())            .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)            .AddEnvironmentVariables()            .AddCommandLine(args)            .Build();

        // Reading simple values        string appName = configuration["AppSettings:AppName"];        Console.WriteLine($"App Name: {appName}");

        // Reading nested sections        string connString = configuration.GetConnectionString("DefaultConnection");        Console.WriteLine($"Connection String: {connString}");

        // Reading an integer        int maxRetries = int.Parse(configuration["AppSettings:MaxRetries"]);        Console.WriteLine($"Max Retries: {maxRetries}");

        // Getting an entire section        var appSettingsSection = configuration.GetSection("AppSettings");        Console.WriteLine($"Version: {appSettingsSection["Version"]}");    }}

Options Pattern (Binding to Classes)

The best practice is to use strongly typed configuration via IOptions<T>. To do this:

1. Create a class for the configuration section:

public class AppSettings{    public string AppName { get; set; }    public string Version { get; set; }    public int MaxRetries { get; set; }}

2. Register the configuration in the DI container (for ASP.NET Core or using Micros