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home / developersection / interviews / how does configuration work in asp.net core?
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Utpal Vishwas
Utpal Vishwas

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I am Utpal Vishwas from Uttar Pradesh. Have completed my B. Tech. course from MNNIT campus Prayagraj in 2022. I have good knowledge of computer networking.

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1 Answers

Utpal Vishwas
Utpal Vishwas 20 May 2025
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In ASP.NET Core, configuration is centralized and flexible, allowing you to load settings from multiple sources like:

  1. appsettings.json
  2. Environment variables
  3. Command-line arguments
  4. Secrets (for development)
  5. Custom providers (e.g., Azure Key Vault)

Key Concepts

1. Configuration is Loaded at Startup

Configuration is typically built in Program.cs using:

var builder = WebApplication.CreateBuilder(args);

This line automatically loads configuration from:

  1. appsettings.json
  2. appsettings.{Environment}.json
  3. Environment variables
  4. Command-line args

Common Configuration Sources

Source Purpose
appsettings.json Default config (key-value pairs)
appsettings.Development.json Overrides for dev environment
Environment variables Useful for containerized/cloud setups
Command-line args For runtime overrides
User secrets Secure storage of dev-only secrets

appsettings.json Example

{
  "AppSettings": {
    "SiteName": "MySite",
    "PageSize": 10
  }
}

Accessing Configuration

1. Via IConfiguration

public class HomeController : Controller
{
    private readonly IConfiguration _config;

    public HomeController(IConfiguration config)
    {
        _config = config;
    }

    public IActionResult Index()
    {
        string siteName = _config["AppSettings:SiteName"];
        return Content($"Welcome to {siteName}");
    }
}

2. Using Strongly-Typed Settings

a. Create a class:

public class AppSettings
{
    public string SiteName { get; set; }
    public int PageSize { get; set; }
}

b. Bind in Program.cs:

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

c. Inject via IOptions<AppSettings>:

public class HomeController : Controller
{
    private readonly AppSettings _settings;

    public HomeController(IOptions<AppSettings> options)
    {
        _settings = options.Value;
    }

    public IActionResult Index()
    {
        return Content($"Page size is {_settings.PageSize}");
    }
}

Environment-based Config Files

ASP.NET Core supports automatic environment configuration:

var builder = WebApplication.CreateBuilder(args);

This loads:

  • appsettings.json
  • appsettings.Development.json (based on ASPNETCORE_ENVIRONMENT)

Set environment via:

set ASPNETCORE_ENVIRONMENT=Development

Summary

Concept How it Works
Load settings builder.Configuration
Inject settings Via IConfiguration or IOptions<T>
Environment support appsettings.{Env}.json auto-loaded
Secure secrets Use dotnet user-secrets in development
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