GuruHub: Role of Kestrel server in .Net Core

Kestrel is a cross-platform web server built into ASP.NET Core and is used to handle HTTP requests. It is the default web server that comes with .NET Core applications. Here’s a breakdown of Kestrel's role and importance in .NET Core applications:

1. Default Web Server for ASP.NET Core:

When you create and run an ASP.NET Core application, Kestrel is the underlying server that processes HTTP requests.
It is designed to be lightweight and fast, suitable for high-performance scenarios.

2. Cross-Platform Compatibility:

Kestrel is cross-platform, meaning it runs on Windows, Linux, and macOS.
This aligns with the overall .NET Core philosophy of being cross-platform.

3. High Performance:

Kestrel is optimized for speed and can handle a large number of concurrent connections, making it a great option for microservices or APIs.
It leverages asynchronous I/O and is built on top of libuv (originally), a high-performance library that provides event-driven asynchronous I/O. In newer versions, Kestrel uses managed sockets.

4. Designed for Both Internal and External Requests:

Kestrel can be used as an internet-facing server (directly handling requests from clients over the web) or as a reverse proxy server behind other servers (like IIS or Nginx).
In production, Kestrel is often used behind a reverse proxy (like IIS, Nginx, or Apache) for additional security features like request filtering, SSL termination, and load balancing.

5. Configurable:

Kestrel allows you to configure various options like port binding, SSL, request size limits, and logging.
For example, you can bind Kestrel to specific IP addresses and ports by configuring it in the Program.cs or appsettings.json file.

6. Security:

While Kestrel is fast and lightweight, it lacks some of the advanced security features found in traditional web servers (such as IIS or Nginx). Therefore, it’s often recommended to use it in conjunction with a reverse proxy in production environments.

Summary of Use Cases:

Development and Testing: Kestrel can be used standalone during development for fast iteration.
Production: In production environments, Kestrel is often paired with a reverse proxy for handling external traffic.

Example of Kestrel in ASP.NET Core:

In the Program.cs file of an ASP.NET Core application, Kestrel is typically configured like this:

public class Program

{

public static void Main(string[] args)

{

CreateHostBuilder(args).Build().Run();

}

public static IHostBuilder CreateHostBuilder(string[] args) =>

Host.CreateDefaultBuilder(args)

.ConfigureWebHostDefaults(webBuilder =>

{

webBuilder.UseKestrel(); // This configures Kestrel as the web server

webBuilder.UseStartup<Startup>();

});

}

In summary, Kestrel is an integral part of .NET Core applications, offering high performance, flexibility, and cross-platform support as a web server. It is suitable for both development and production environments (especially when used with a reverse proxy for the latter).