• Cross-Platform: Runs on Windows, Linux, and macOS.
• High Performance: Lightweight and optimized for performance.
• Modularity: Uses a middleware pipeline that is highly configurable.
• Built-in Dependency Injection: Encourages loosely coupled design.
• Cloud-Ready: Designed to integrate well with modern cloud services.
• Open Source: Active community support and frequent updates.

The Startup class is central to ASP.NET Core applications. It configures:

• Services: Through the ConfigureServices method by adding components (e.g., MVC, EF Core, logging) to the DI container.
• Middleware Pipeline: Through the Configure method by setting up the request handling pipeline.

ConfigureServices is where you register application services with the dependency injection container. This can include framework services (MVC, Razor Pages, Entity Framework) and custom application services.

Example:

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllersWithViews();
    services.AddDbContext<ApplicationDbContext>(options =>
        options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));
}

The Configure method defines the HTTP request pipeline by adding middleware components. The order in which middleware is added is crucial as it determines how HTTP requests are processed.

Example:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
        app.UseDeveloperExceptionPage();
    else
        app.UseExceptionHandler("/Home/Error");

    app.UseStaticFiles();
    app.UseRouting();
    app.UseAuthentication();
    app.UseAuthorization();

    app.UseEndpoints(endpoints =>
    {
        endpoints.MapControllerRoute(
            name: "default",
            pattern: "{controller=Home}/{action=Index}/{id?}");
    });
}

Settings are typically configured using:

• appsettings.json: The main configuration file.
• Environment-Specific Files: Such as appsettings.Development.json.
• Environment Variables and Command-Line Arguments: Which can override settings.

The configuration system supports hierarchical settings and binding to strongly typed classes via the Options pattern.

The appsettings.json file holds configuration data (like connection strings, logging settings, etc.) in a JSON format. It can be supplemented by environment-specific files and overridden by other configuration sources.

Create separate configuration files named with the environment suffix (e.g., appsettings.Development.json, appsettings.Production.json). Set the environment by defining the ASPNETCORE_ENVIRONMENT variable. The configuration system automatically loads the appropriate file based on the environment.

ASP.NET Core provides a built-in logging API through the ILogger interface. It supports multiple providers (Console, Debug, EventSource) and can be extended with third-party logging frameworks like Serilog or NLog.

Example:

public class HomeController : Controller
{
    private readonly ILogger<HomeController> _logger;
    public HomeController(ILogger<HomeController> logger)
    {
        _logger = logger;
    }

    public IActionResult Index()
    {
        _logger.LogInformation("Index page requested");
        return View();
    }
}

Kestrel is the default, cross-platform web server for ASP.NET Core. It is designed to be lightweight and high performance. In production, it is often used in combination with a reverse proxy like IIS, Nginx, or Apache for additional security and robustness.