These notes include: Learn > .NET > ASP.NET Core > Fundamentals > Options | Environments

Abstract

ASP.NET Core web applications function as console applications. By default, they use Kestrel as the web server.

Web App Frameworks

• Server-rendered Apps
  • ASP.NET Core Razor Pages
  • ASP.NET Core MVC
  • Blazor Server
• Client-rendered Apps
  • Blazor WASM
  • ASP.NET Core SPA (w/Angular or React)
• Hybrid
• Web APIs
  • Controller-based API
  • Minimal API
• Real-time Apps
• RPC Apps
  • gRPC

Fundamentals (Common to all ASP.NET app models)

Project Structure

• Pages/ — Razor pages and supporting files.
  • .cshtml file with HTML markup with C# code using Razor syntax
  • .cshtml.cs C# code that handles page events
  • _Layout.cshtml configures UI elements common to all pages; sets up nav menu at top of page and copyright at bottom of page.
• wwwroot/
  • Static assets (HTML, JS, CSS files)
• appsettings.json
  • Configuration data.
• Program.cs
  • Services are configured.
  • Request handling pipeline (middleware) is defined.
• Models/
  • Add this to hold the data models.

Dependency Injection

• Makes configured services available throughout an app.
• Services are added to the DI container with WebApplicationBuilder.Services.
• When WebApplicationBuilder is instantiated, many framework-provided services are added.

Middleware

The request handling pipeline is composed of a series of middleware components.
Each component performs operations on an HttpContext and either:

1. Invokes the next middleware in the pipeline, or;
2. Terminates the request.

Middleware components are added to the pipeline with the UseFeature convention:

// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Error");
    app.UseHsts();
}

app.UseHttpsRedirection(); // Redirect HTTP requests to HTTPs
app.UseStaticFiles();

app.UseAuthorization();

Host

ASP.NET Core apps build a Host on startup. The host encapsulates all of the app’s resources:

• An HTTP server
• Middleware
• Logging
• DI services
• Configuration

3 different hosts

• .NET Minimal Host (recommended; used by default in templates)
• .NET WebApplication Host
• .NET Generic Host (similar to Minimal); allows other types of apps (not web apps) to use framework extensions like logging, DI, configuration, etc.
• ASP.NET Core Web Host (deprecated)

Instantiate a host

WebApplication app = builder.Build();

The host is instantiated with these default options:

• Kestrel web server w/IIS integration
• Configuration from appsettings.json, environment variables, command line arguments, other.
• Logging output to console and debug providers.

Servers

ASP.NET Core apps use an HTTP server to listen for HTTP requests. In Windows, the options are:

• Kestrel—cross-platform; can run as a reverse proxy; can run as a public-facing edge server exposed to the Internet.
• IIS HTTP Server—ASP.NET Core app and IIS run in the same process.
• HTTP.sys

Options

See also: Options pattern in ASP.NET Core | Microsoft Learn

Environments

See also: Use multiple environments in ASP.NET Core | Microsoft Learn ASP.NET Core supports environments such as Development, Staging, and Production.
ASPNETCORE_ENVIRONMENT environment variable specifies the environment in which the app is running.

This example configures the exception handler and HSTS when not running in Development environment:

if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Error");
    app.UseHsts();
}

Make HTTP Requests

An implementation of IHttpClientFactory is available for creating HttpClient instances. Register and configure one client for calling an API. Register and configure the default client for all other purposes.

Content Root

The base path for: the executable hosting the app (.exe); compiled assemblies (.dll); content files (Razor (.cshtml, .razor); configuration files (.json, .xml); data files (.db)); the web root (wwwroot folder).

During development, content root is the project’s root directory. Content root can be changed when building the host.

Web Root

The base path for public, static resource files: Stylesheets, JavaScript, Images. Default path = CONTENT_ROOT/wwwroot. Web root can be changed when building the host.