ASP.NET Core Fundamentals

ASP.NET Core is the web framework in .NET. You use it to build HTTP APIs, server-rendered web applications, real-time services, and backends for other clients.

The framework gives you a web server, a request pipeline, routing, dependency injection, configuration, logging, security integration, and several endpoint models. You choose which parts your application needs.

ASP.NET Core is open source and cross-platform. It runs on Windows, Linux, and macOS. It works well when your team uses C# and .NET, needs one framework for APIs and web interfaces, or wants explicit control over the HTTP pipeline.

It may be a poor fit when your team has no .NET expertise, a static site is enough, or another platform already owns the application's operational model. ASP.NET Core supplies web infrastructure. It does not choose your domain model, database design, deployment topology, or security policy.

Start with the host

Every ASP.NET Core application starts by building a host. The host owns the resources needed to run the application:

The HTTP server accepts connections.
The middleware pipeline processes requests and responses.
The service container creates registered dependencies.
Configuration provides settings.
Logging providers receive log events.
Application lifetime signals coordinate startup and shutdown.

Current application templates use WebApplicationBuilder and WebApplication for this setup.

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddProblemDetails();

var app = builder.Build();

app.UseExceptionHandler();
app.MapGet("/", () => "Hello from ASP.NET Core");

app.Run();

Read this file in two phases. Calls on builder.Services register capabilities before the host is built. Calls on app assemble the request pipeline and map endpoints after the build.

Kestrel is the default cross-platform web server. It can serve Internet traffic directly. Many production deployments place it behind IIS, Nginx, Apache, a load balancer, or an ingress controller. The proxy and application must agree about the original client address, scheme, host, and request limits.

ASP.NET Core Fundamentals

ASP.NET Core Fundamentals

Start with the host

Follow one request through the pipeline

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