ASP.NET Core Configuration: appsettings.json, Environment Variables, and Options

ASP.NET Core applications commonly need settings such as connection strings, API URLs, feature flags, and logging options. The built-in configuration system provides a consistent way to load and consume those values.

📄 appsettings.json

A simple configuration file can contain application settings:

{
  "AppSettings": {
    "ApplicationName": "MyApp",
    "TimeoutSeconds": 30
  }
}

ASP.NET Core loads appsettings.json automatically in the standard application setup.

🌍 Environment-Specific Settings

You can provide environment-specific configuration with files such as appsettings.Development.json and appsettings.Production.json. This allows development and production settings to remain separate.

🔐 Environment Variables

Sensitive or deployment-specific values can be supplied through environment variables instead of being committed to source control.

var connectionString =
    builder.Configuration.GetConnectionString("DefaultConnection");

For nested configuration values, environment-variable providers support hierarchical keys.

⚡ Reading Configuration Directly

var appName = builder.Configuration["AppSettings:ApplicationName"];
var timeout = builder.Configuration.GetValue<int>(
    "AppSettings:TimeoutSeconds");

This is convenient for a small number of values, but larger groups of related settings are usually easier to manage with the Options pattern.

🧩 Strongly Typed Options

public class AppSettings
{
    public string ApplicationName { get; set; } = "";
    public int TimeoutSeconds { get; set; }
}

builder.Services.Configure<AppSettings>(
    builder.Configuration.GetSection("AppSettings"));

A service can then consume the settings through IOptions<AppSettings>.

🚫 Don't Store Secrets in Source Control

Passwords, production connection strings, API keys, and other secrets should not normally be committed to a public repository. Use environment variables, a secret store, or your hosting platform's secret configuration.

🧠 Key Takeaway

ASP.NET Core configuration is layered and flexible. Use simple configuration access for occasional values and strongly typed options when a feature has several related settings.

Continue with ⚡ ASP.NET Core Tutorials.

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