Configuration Management in .NET Core with appsettings.json

A comprehensive guide to leveraging appsettings.json for flexible configuration management in .NET Core applications.

Quick Start

1. Create appsettings.json

{
  "AppSettings": {
    "LogLevel": "Warning",
    "ConnectionStrings": {
      "Default": "Server=localhost;Database=mydb;"
    }
  }
}

2. Basic Configuration Loading

using Microsoft.Extensions.Configuration;

var config = new ConfigurationBuilder()
    .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
    .Build();

string logLevel = config["AppSettings:LogLevel"];
string connectionString = config["AppSettings:ConnectionStrings:Default"];

Core Features

1. Value Retrieval Methods

// Traditional string access
var logLevel = config["AppSettings:LogLevel"];

// Type-safe retrieval
int timeout = config.GetValue<int>("Network:Timeout", 30); // Default value

// Connection string shortcut
var dbConn = config.GetConnectionString("Default");

2. Multi-Environment Configuration

appsettings.Development.json

{
  "AppSettings": {
    "LogLevel": "Debug",
    "DebugMode": true
  }
}

Configuration Builder

var config = new ConfigurationBuilder()
    .AddJsonFile("appsettings.json") // Base configuration
    .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
    .Build();

Configuration Priority:

Command-line arguments
Environment variables
Environment-specific JSON
Base appsettings.json

Advanced Techniques

1. Strongly-Typed Configuration

Configuration Class

public class AppSettings
{
    public string LogLevel { get; set; }
    public DatabaseConfig Database { get; set; }

    public class DatabaseConfig
    {
        public string Host { get; set; }
        public int Port { get; set; }
    }
}

Binding Configuration

var appConfig = config.GetSection("AppSettings").Get<AppSettings>();
Console.WriteLine($"DB Port: {appConfig.Database.Port}");

2. Dynamic Reloading

var reloadToken = config.GetReloadToken();
reloadToken.RegisterChangeCallback(_ => 
{
    Console.WriteLine("Configuration changed!");
    // Refresh configuration-sensitive components
}, null);

Runtime Configuration Sources

1. Environment Variables

# Linux/macOS
export AppSettings__LogLevel=Verbose

# Windows
set AppSettings__LogLevel=Verbose

2. Command-Line Arguments

var config = new ConfigurationBuilder()
    .AddCommandLine(args)
    .Build();

Execution Example

dotnet run --AppSettings:LogLevel=Critical

Best Practices

Security Considerations

// Never store secrets in appsettings.json
var secret = config["Azure:KeyVaultSecret"];

Validation Pattern

services.Configure<AppSettings>(config.GetSection("AppSettings"))
        .ValidateDataAnnotations();

Custom Configuration Providers

public class DatabaseConfigurationProvider : ConfigurationProvider
{
    public override void Load()
    {
        // Load config from database
        Data = GetConfigFromDB();
    }
}

Key Limitations

No Native Write Support: Configuration system is read-only
Type Conversion Requirements: Manual handling for complex types
Environment-Specific Complexity: Requires careful management of multiple files

Recommended NuGet Packages

Microsoft.Extensions.Configuration.Json
Microsoft.Extensions.Configuration.EnvironmentVariables
Microsoft.Extensions.Configuration.CommandLine
Microsoft.Extensions.Options.ConfigurationExtensions

Official Configuration Documentation Configuration Best Practices

Next Steps: Explore integration with HostBuilder and dependency injection for enterprise-level configuration management.

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