How is configuration handled in ASP.NET Core?

Configuration is handled using IConfiguration interface and supports sources like appsettings.json, env variables, and secrets.

What is IOptions used for?

It binds config sections to strongly-typed classes and is injected via DI.

Configuration Handling in ASP.NET Core | FullStackPrep.Dev

💡 Concept Name

Configuration in ASP.NET Core

📘 Quick Intro

ASP.NET Core provides a flexible configuration system that reads settings from various sources like appsettings.json, environment variables, and secrets. It uses dependency injection to provide access to these settings throughout the app.

🧐 Analogy / Short Story

Think of configuration as ordering food through a delivery app. You specify your preferences (address, cuisine, toppings). The app doesn’t hardcode what you want—it reads your configuration. ASP.NET Core reads settings similarly, adapting behavior without changing code.

🔧 Technical Explanation

Configuration in ASP.NET Core is built on the IConfiguration interface. It supports:

appsettings.json and appsettings.{Environment}.json
Environment Variables
User Secrets (in development)
Command-line arguments
Azure Key Vault, JSON, INI, XML, etc.

You can inject IConfiguration directly or bind configuration sections to strongly-typed classes using IOptions<T>.

🎯 Purpose & Use Case

✅ Store connection strings and API keys
✅ Manage per-environment settings (dev/staging/prod)
✅ Externalize feature toggles or flags
✅ Secure sensitive info using secrets or Key Vault

💻 Real Code Example

// appsettings.json
{
  "AppSettings": {
    "Title": "FullStackPrep.Dev"
  }
}

// Settings class
public class AppSettings {
    public string Title { get; set; }
}

// Program.cs (ASP.NET Core 6+)
builder.Services.Configure<AppSettings>(builder.Configuration.GetSection("AppSettings"));

// Controller
public class HomeController : Controller {
    private readonly AppSettings _settings;
    public HomeController(IOptions<AppSettings> options) => _settings = options.Value;
    public IActionResult Index() => Content($"Title: {_settings.Title}");
}

❓ Interview Q&A

Q1: What is IConfiguration?
A: Interface to access key-value based configuration data in .NET Core.

Q2: What file commonly stores settings?
A: appsettings.json

Q3: How to bind a config section to a class?
A: Using services.Configure<T>().

Q4: What does IOptions<T> provide?
A: Access to strongly-typed config values via DI.

Q5: Can configuration change per environment?
A: Yes, using appsettings.Development.json, etc.

Q6: What are the config sources in order?
A: Command-line args > Env vars > appsettings.json

Q7: What is User Secrets used for?
A: Store sensitive config in development.

Q8: Can Azure Key Vault be used?
A: Yes, for secure production secrets.

Q9: What is the default config system based on?
A: Microsoft.Extensions.Configuration

Q10: How to read a single config value?
A: Use Configuration["Key"] or GetValue<T>("Key")

📝 MCQs

Q1. What is IConfiguration in ASP.NET Core?

A class for logging
An interface to access config data
A middleware for caching
A controller filter

Q2. Which file stores configuration by default?

web.config
launchSettings.json
appsettings.json
settings.xml

Q3. What does IOptions<AppSettings> provide?

Logging setup
Database access
Strongly-typed config values
Routing information

Q4. Which config source has highest priority?

appsettings.json
Environment variables
Command-line arguments
launchSettings.json

Q5. How to register settings class?

services.Inject<T>()
services.Register<T>()
services.Configure<T>()
services.Map<T>()

Q6. What is the use of User Secrets?

Store static files
Store dev-only sensitive info
Enable logging
Add middleware

Q7. What namespace contains config system?

System.Configuration
Microsoft.Hosting
Microsoft.Extensions.Configuration
System.Web

Q8. How to inject configuration in controller?

Using ViewData
Using IActionResult
Using IConfiguration or IOptions
Using HttpContext

Q9. Which pattern is used for config binding?

Repository Pattern
Service Pattern
Factory Pattern
Options Pattern

Q10. What method gets single config value?

GetService<T>()
UseSetting()
AddConfig()
GetValue<T>(key)

💡 Bonus Insight

You can chain multiple configuration providers for hybrid config (e.g., use appsettings + env vars + Key Vault). Always validate settings using ValidateDataAnnotations() for critical apps.

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How is Configuration Handled in ASP.NET Core?