Kestrel web server is an open-source (source code is available on GitHub), event-driven, asynchronous I/O based server used to host ASP.NET applications on any platform. It’s a listening server that have a Command-Line Interface (CLI). This listening server can be installed on a Windows or Linux web server and then the command-line interface on your computer.

It was launched by Microsoft alongside ASP.NET Core. By default, All ASP.NET Core application can utilize a new MVC framework and the Kestrel web server.

A Detailed Explanation of the Kestrel Web Server

Kestrel is considered a preferred web server for newer ASP.NET applications (see comparison of Kestrel to IIS and why you need the both servers). Kestrel is however based on the libuv library, This is the same library used by Node.js. Libuv supports an event-driven style of programming. The following highlights Some of its core utilities:

• Non-blocking network support
• Asynchronous file system access
• Timers
• Child processes

In addition, it allows ASP.NET Core applications to be run easily on other cross-platform webservers such as Nginx and Apache, without the need to address varying startup configurations.

By using Kestrel as an in-process server, applications will have a consistent process such as (Startup (Main (), Startup.ConfigireServices(), Startup.Configure()) ) even with cross-platform support.

Benefits of Kestrel Web Server

Kestrel has support on all platforms and versions supported by .NET Core. Furthermore, it is included by default in ASP.NET Core new project templates and can provide better request processing performance. When you create a new project in Visual Studio, your project is automatically configured to run in Kestrel web server by defaut.

As stated earlier, it’s not a fully-featured web server, but that’s precisely why it’s fast. If you feel the need for speed, Kestrel is the answer–especially since it is designed to be used in production for ASP.NET.

What you can do is run it behind a more fully-featured webserver such as IIS or NGINX. You can run it behind IIS using the HttpPlatformHandler or behind IIS Express using HttpPlatformHandler by Visual Studio. Moreover, you’ll want to support it in your ASP.NET Core projects so that they can be conveniently run by developers on any of the supported platforms.

Also, even if you are not working cross-platform, you can run ASP.NET on a web server straight from the command line.

In Conclusion

Since Kestrel is not a fully-featured web server, it is advisable to run it behind IIS  or NGINX. It was designed to make ASP.NET Core as fast as possible but it is as well limited in its ability to manage security, serve static files and perform other crutial functions of a fully fledged web server.