What is the role of IIS and Kestrel in hosting ASPNET Core applications

When it comes to hosting ASP.NET Core applications, two key components are often discussed: Kestrel and Internet Information Services (IIS). Understanding the roles of these two web servers is essential for effectively deploying and managing ASP.NET Core applications.

1. Kestrel Web Server

Kestrel is a cross-platform web server that is included by default with ASP.NET Core applications. It is designed to be lightweight and fast, making it suitable for serving dynamic web applications. Kestrel can run on Windows, Linux, and macOS, and it is often used in development and production environments.

Key Features of Kestrel

Cross-Platform: Kestrel can run on any operating system that supports .NET Core.
High Performance: Kestrel is optimized for performance and can handle a large number of concurrent connections.
Lightweight: Kestrel has a small footprint and is easy to configure.

Sample Code for Configuring Kestrel

        
            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.UseStartup<Startup>();
                            webBuilder.UseKestrel(); // Use Kestrel as the web server
                        });
            }

In this example, the CreateHostBuilder method configures Kestrel as the web server for the ASP.NET Core application. The application will listen for incoming HTTP requests on the specified ports.

2. Internet Information Services (IIS)

IIS is a web server developed by Microsoft for hosting web applications on Windows servers. While Kestrel can serve requests directly, IIS is often used as a reverse proxy in front of Kestrel for several reasons.

Key Features of IIS

Reverse Proxy: IIS can act as a reverse proxy, forwarding requests to Kestrel and handling tasks such as SSL termination, URL rewriting, and load balancing.
Application Pool Management: IIS provides robust application pool management, allowing for better isolation and resource management of web applications.
Security Features: IIS includes built-in security features such as request filtering, authentication, and authorization.

Sample Code for Configuring IIS with ASP.NET Core

To host an ASP.NET Core application with IIS, you need to install the ASP.NET Core Hosting Bundle on the server. This bundle includes the .NET Core Runtime, libraries, and the ASP.NET Core Module for IIS.

Steps to Configure IIS

Install the ASP.NET Core Hosting Bundle on your Windows Server.
Open IIS Manager and create a new site:

Right-click on Sites and select Add Website.
Set the Site name, Physical path (pointing to the published folder), and Port.

Configure the application pool to use No Managed Code.
Set permissions for the IIS user to access the published folder.

3. How IIS and Kestrel Work Together

In a typical deployment scenario, IIS acts as a reverse proxy server that forwards incoming HTTP requests to Kestrel. This setup allows you to take advantage of the features provided by both servers:

IIS handles incoming requests, SSL termination, and static file serving.
Kestrel processes the application logic and serves dynamic content.

This combination provides a robust and secure hosting environment for ASP.NET Core applications.

Conclusion

In summary, Kestrel is a lightweight, high-performance web server that is ideal for serving ASP.NET Core applications, while IIS provides additional features such as reverse proxy capabilities, application pool management, and enhanced security. Together, they create a powerful hosting solution for modern web applications.