What is ASP.NET Core, and how is it different from ASP.NET MVC 5?

ASP.NET Core is a cross-platform, open-source framework for building modern web

applications, APIs, and microservices. It’s a complete rewrite of the old ASP.NET

framework, designed to be lightweight, modular, and cloud-ready.

Key Differences:

Feature ASP.NET MVC 5 ASP.NET Core

Platform Windows only Cross-platform (Windows, macOS, Linux)

Hosting IIS only Kestrel, IIS, Nginx, Apache, self-hosting

Configuration web.config (XML) appsettings.json (JSON-based)

Dependency Injection Third-party libraries Built-in DI container

Modularity Monolithic Modular via NuGet packages

Example:

In ASP.NET MVC 5, you’d deploy only to IIS on Windows. In ASP.NET Core, the same app

can run on a Linux server using Nginx + Kestrel — perfect for Docker or cloud

environments.

⚙ 2. Explain the request-processing pipeline in

ASP.NET Core.

ASP.NET Core handles incoming requests through a middleware pipeline. Each

middleware can process, modify, or short-circuit requests before they reach the endpoint.

Flow Example:

Request → Middleware 1 (Logging)

→ Middleware 2 (Authentication)

→ Middleware 3 (Routing)

→ Controller / Endpoint

→ Response → Back through pipeline

Follow :

Example:

If you log requests, check authentication, and handle static files — they execute in the order

you add them in Program.cs.

app.UseStaticFiles();

app.UseRouting();

app.UseAuthentication();

app.UseAuthorization();

app.MapControllers();

🧱 3. What is Kestrel?

Kestrel is a cross-platform web server built into ASP.NET Core. It’s fast, lightweight, and

serves as the default web server. You can run it standalone or behind a reverse proxy like

IIS or Nginx.

Real Example:

When you run dotnet run, your app listens on

— that’s

Kestrel serving your app.

🖥 4. What is the role of IIS when hosting ASP.NET

Core apps?

IIS acts as a reverse proxy. It forwards incoming HTTP requests to the Kestrel server

running your ASP.NET Core app. This setup provides:

• Process management (auto-restart)
• Port sharing (multiple sites)
• Windows authentication
• Logging and monitoring

Follow :

In short: IIS → forwards → Kestrel → runs the app.

🚀 5. What is the Startup class used for?

The Startup class defines how your app configures services (DI, authentication, etc.)

and sets up middleware (routing, static files, error pages, etc.).

Example:

public class Startup

public void ConfigureServices(IServiceCollection services)

services.AddControllers();

public void Configure(IApplicationBuilder app)

app.UseRouting();

app.UseEndpoints(endpoints => endpoints.MapControllers());

🧭 6. Explain the purpose of Program.cs in .NET 6+.

In .NET 6+, Startup.cs and Program.cs merged into one minimal host configuration

file.

It sets up the web host, configuration, logging, and middleware pipeline.

Example:

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddControllers();

var app = builder.Build();

Follow :

app.MapControllers();

app.Run();

It’s simpler, faster, and easier to read.

🔹 7. What is a Minimal API?

Minimal APIs are a lightweight way to build small HTTP APIs without controllers or

attributes. Perfect for microservices.

Example:

var app = WebApplication.Create(args);

app.MapGet("/hello", () => "Hello World!");

app.Run();

This single file can run a full REST endpoint.

🧰 8. What is the WebApplicationBuilder in .NET 6/7/8?

WebApplicationBuilder simplifies creating and configuring a web host. It combines:

• IHostBuilder
• WebHostBuilder
• Configuration
• Services

Example:

var builder = WebApplication.CreateBuilder(args);

Follow :

builder.Services.AddDbContext<AppDbContext>();

builder.Services.AddControllers();

Then you call builder.Build() to create the WebApplication.

🛣 9. How does routing work in ASP.NET Core MVC?

Routing maps incoming URLs to controllers and actions.

ASP.NET Core uses Endpoint Routing to decide which route matches a request.

Example:

app.MapControllerRoute(

name: "default",

pattern: "{controller=Home}/{action=Index}/{id?}");

If the user visits /product/details/5, it maps to:

ProductController → Details(int id = 5).

🏷 10. Difference between Conventional and Attribute

Routing.

Type Definition Example

Conventional

Routing

Routes defined in

Program.cs or

Startup.cs.

{controller=Home}/{action=Ind

ex}/{id?}

Attribute

Routing

Routes defined with

attributes on controller

actions.

[Route("api/products/{id}")]

Example:

[Route("api/[controller]")]

Follow :

public class ProductsController : ControllerBase

[HttpGet("{id}")]

public IActionResult Get(int id) => Ok($"Product {id}");

🧩 11. What is Endpoint Routing?

Endpoint routing separates route matching from execution.

It lets middleware (like authentication) know which endpoint will be executed before it

runs.

Example:

app.UseRouting();

app.UseAuthorization();

app.UseEndpoints(endpoints => endpoints.MapControllers());

🔄 12. Explain the role of middleware in ASP.NET Core.

Middleware are components that handle requests and responses in a pipeline. Each

can:

• Process requests
• Call the next middleware
• Or short-circuit the pipeline

Example:

A logging middleware that runs before all others:

app.Use(async (context, next) =>

Console.WriteLine("Request: " + context.Request.Path);

Follow :

await next();

});

🕒 13. What is the order of middleware execution?

Middleware execute in the order they’re added in Program.cs.

Response flows in reverse order back up the chain.

Tip:

• Authentication must come before Authorization.
• UseRouting must come before UseEndpoints.

🧩 14. How to create custom middleware?

Example:

public class RequestLoggingMiddleware

private readonly RequestDelegate _next;

public RequestLoggingMiddleware(RequestDelegate next) => _next =

next;

public async Task Invoke(HttpContext context)

Console.WriteLine($"Request for: {context.Request.Path}");

await _next(context);

Register it:

app.UseMiddleware<RequestLoggingMiddleware>();

Follow :

🧱 15. What is the difference between middleware and

filters?

Feature Middleware Filter

Scope Entire app Controller/action level

Runs on Every request MVC actions only

Example Authentication, logging Validation, exception filters

⚒ 16. Explain the IApplicationBuilder interface.

IApplicationBuilder builds the middleware pipeline.

You use it in Startup.Configure() or Program.cs to add middleware via Use, Run,

and Map.

🔀 17. Difference between Use, Run, and Map in

middleware.

Metho

Description Example

Use Adds middleware that can call

the next component.

app.UseMiddleware<Logging>();

Run Terminates the pipeline — no

next middleware.

app.Run(async c => await

c.Response.WriteAsync("End"));

Map Branches pipeline based on

request path.

app.Map("/admin", a =>

a.Run(...));

Follow :

🏗 18. What are Hosting Models in ASP.NET Core

(In-process vs Out-of-process)?

Model Description Performance

In-process App runs inside IIS worker process

(w3wp.exe).

Faster (single

process)

Out-of-proces

IIS acts as reverse proxy to Kestrel. Slight overhead

Example:

For Windows servers, in-process gives best performance. For cross-platform Docker, use

out-of-process.

🌍 19. Explain Web Host vs Generic Host.

Host Type Used For Example

Web Host Web apps (ASP.NET Core ≤ 2.2) WebHost.CreateDefaultBui

lder()

Generic

Host

Any app: web, worker, console (≥ 3.0) Host.CreateDefaultBuilde

r()

Generic Host unifies background tasks, APIs, and services in one model.

⚙ 20. How does configuration binding work in

ASP.NET Core?

ASP.NET Core can automatically bind configuration from:

• appsettings.json
• Environment variables

Follow :

• Command-line arguments

Example:

// appsettings.json

"AppSettings": {

"SiteName": "MyShop",

"Version": "1.0"

// POCO

public class AppSettings

public string SiteName { get; set; }

public string Version { get; set; }

// Program.cs

builder.Services.Configure<AppSettings>(

builder.Configuration.GetSection("AppSettings"));

You can inject IOptions<AppSettings> anywhere.

MVC Architecture & Controllers