Kestrel is a cross-platform web server that is built into the .NET Core runtime. It is the default web server for ASP.NET Core applications and is responsible for processing incoming requests and returning responses to clients.
In this post, we’ll take an in-depth look at Kestrel, its features, and how it works under the hood. We’ll also explore some best practices for using Kestrel in your own ASP.NET Core applications.
What is Kestrel server in .net?
Kestrel is a lightweight, open-source web server that is optimized for handling high levels of concurrent connections. It was designed to be cross-platform, which means that it can be used on Windows, Linux, and macOS.
One of the key advantages of Kestrel is its performance. Because it is built on top of the .NET Core runtime, it is able to take advantage of many of the performance improvements that have been made to the .NET Core platform over the years. This allows Kestrel to handle a large number of requests with minimal overhead.
Another advantage of Kestrel is its flexibility. It is designed to be modular and extensible, which means that it can be customized to meet the specific needs of your application. For example, you can configure Kestrel to use SSL/TLS encryption, to support WebSockets, or to integrate with other web servers such as IIS or Apache.
How does Kestrel server in .net work?
Kestrel is built on top of the libuv library, which is a cross-platform library for asynchronous I/O. This allows Kestrel to handle incoming requests and outgoing responses without blocking the main thread of the application.
When a request comes in, Kestrel creates a new HttpRequest object and passes it to the middleware pipeline. Each middleware component in the pipeline has the opportunity to modify the request, perform some action, and then pass the request on to the next middleware component.
Once the middleware pipeline has completed, the final response is returned to the client. Kestrel uses the HttpResponse object to construct the response and sends it back to the client.
Kestrel can also be used in conjunction with other web servers such as IIS or Apache. In this scenario, Kestrel is used as a reverse proxy, which means that it sits in front of the other web server and handles incoming requests before passing them on to the other server for processing.
Best practices for using Kestrel server in .net
When using Kestrel in your own ASP.NET Core applications, there are a number of best practices that you should follow to ensure that your application is secure, scalable, and maintainable.
Configure Kestrel to use HTTPS
By default, Kestrel listens for incoming requests over HTTP. However, it is recommended that you configure Kestrel to use HTTPS instead. This will encrypt all data transmitted between the client and the server, which is important for protecting sensitive data such as passwords or credit card information.
To configure Kestrel to use HTTPS, you will need to create a certificate and then configure Kestrel to use that certificate. You can either use a self-signed certificate or obtain a certificate from a trusted certificate authority (CA).
Use a reverse proxy
If you are deploying your ASP.NET Core application to a production environment, it is recommended that you use a reverse proxy such as IIS or Apache to sit in front of Kestrel. This can provide additional security features such as SSL/TLS offloading and load balancing.
When using a reverse proxy, you can configure Kestrel to listen on a local port (such as 127.0.0.1:5000) and then configure the reverse proxy to forward incoming requests to that port. This allows Kestrel to handle incoming requests without exposing it directly to the internet.
Configure connection limits:
By default, Kestrel has a connection limit of 1000. If your application needs to handle more connections, you can increase the limit by configuring the ConnectionManagerOptions.
Use Connection pooling:
Kestrel uses connection pooling to improve performance. By default, Kestrel uses a maximum of 1024 connections per endpoint. You can increase this limit by configuring the ConnectionManagerOptions.
Use Buffering:
Kestrel supports buffering to reduce the overhead of sending small amounts of data. You can enable buffering by setting the appropriate properties in the server options.
How to configure Kestrel server in .net?
Kestrel server can be configured in multiple ways to achieve the desired performance and security levels. Some of the key configuration options include:
Listening endpoint configuration
Kestrel server can be configured to listen on specific IP addresses and ports using the UseUrls() method in the Program.cs file. Here’s an example:
csharp
public static IHostBuilder CreateHostBuilder(string[] args) =>
Host.CreateDefaultBuilder(args)
.ConfigureWebHostDefaults(webBuilder =>
{
webBuilder.UseKestrel()
.UseUrls("http://localhost:5000", "https://localhost:5001")
.UseStartup<Startup>();
});
In the above code, Kestrel is configured to listen on both HTTP and HTTPS protocols on the localhost IP address and the default ports of 5000 and 5001 respectively.
Connection limits configuration
Kestrel server can limit the number of concurrent connections and the number of requests allowed per connection using the Listen() method in the Program.cs file. Here’s an example:
csharp
public static IHostBuilder CreateHostBuilder(string[] args) =>
Host.CreateDefaultBuilder(args)
.ConfigureWebHostDefaults(webBuilder =>
{
webBuilder.UseKestrel(options =>
{
options.Limits.MaxConcurrentConnections = 100;
options.Limits.MaxConcurrentUpgradedConnections = 100;
options.Limits.MaxRequestBodySize = 10 * 1024;
options.Limits.MinRequestBodyDataRate =
new MinDataRate(bytesPerSecond: 100, gracePeriod: TimeSpan.FromSeconds(10));
options.Limits.MinResponseDataRate =
new MinDataRate(bytesPerSecond: 100, gracePeriod: TimeSpan.FromSeconds(10));
options.Listen(IPAddress.Any, 5000);
})
.UseStartup<Startup>();
});
In the above code, Kestrel is configured to limit the number of concurrent connections to 100, the number of requests allowed per connection to an unlimited number, and the maximum request body size to 10KB. Additionally, the minimum request and response data rates are also configured.
SSL configuration
Kestrel server can be configured to use SSL/TLS certificates to encrypt the data transferred between the server and clients. Here’s an example of how to configure SSL in Kestrel:
csharp
public static IHostBuilder CreateHostBuilder(string[] args) =>
Host.CreateDefaultBuilder(args)
.ConfigureWebHostDefaults(webBuilder =>
{
webBuilder.UseKestrel(options =>
{
options.Listen(IPAddress.Any, 5000, listenOptions =>
{
listenOptions.UseHttps("certificate.pfx", "password");
});
})
.UseStartup<Startup>();
});
In the above code, Kestrel is configured to listen on all IP addresses on port 5000 and use the certificate.pfx file with the password password for SSL/TLS encryption.
Request filtering configuration
Kestrel server can be configured to filter incoming requests based on various criteria, such as IP address, port number, and HTTP headers. Here’s an example of how to configure request filtering in Kestrel:
csharp
public static IHostBuilder CreateHostBuilder(string[] args) =>
Host.CreateDefaultBuilder(args)
.ConfigureWebHostDefaults(webBuilder =>
{
webBuilder.UseKestrel(options =>
{
options.Listen(IPAddress.Any, 5000, listenOptions =>
{
listenOptions.UseConnectionLogging();
listenOptions.UseHttps();
listenOptions.UseConnectionHandlerKestrel server is a cross-platform web server that is used to host ASP.NET Core web applications. It is a lightweight and high-performance server that is built using .NET. Kestrel server is used as the default web server in ASP.NET Core applications and is designed to handle high traffic loads with ease. In this post, we will take a deep dive into the Kestrel server in .NET, its features, and how to use it.
Kestrel server features
Here are some of the key features of the Kestrel server in .NET:
- Cross-platform: Kestrel server is a cross-platform web server that can be run on Windows, Linux, and macOS. This makes it a versatile option for hosting ASP.NET Core applications on different platforms.
- Lightweight: Kestrel server is a lightweight web server that has a small footprint. This means that it consumes fewer system resources compared to other web servers.
- High-performance: Kestrel server is designed to be a high-performance web server that can handle large amounts of traffic. It is optimized for serving static files and has support for HTTP/2, WebSockets, and other advanced features.
- Secure: Kestrel server can be configured to use SSL/TLS encryption for secure communication. This ensures that data is transmitted securely over the network.
- Integration with other web servers: Kestrel server can be used as a standalone web server or it can be integrated with other web servers like IIS, Nginx, and Apache.
How to use Kestrel server in .NET
Using Kestrel server in .NET is straightforward. Here are the steps to create a basic ASP.NET Core application that uses Kestrel server:
Step 1: Create a new ASP.NET Core application
Open Visual Studio and create a new ASP.NET Core web application. Choose the ASP.NET Core Web Application template and select the Empty template.
Step 2: Configure Kestrel server
In the Startup.cs file, add the following code to configure Kestrel server:
csharp
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
app.UseRouting();
app.UseEndpoints(endpoints =>
{
endpoints.MapGet("/", async context =>
{
await context.Response.WriteAsync("Hello World!");
});
});
app.UseKestrel();
}
This code configures Kestrel server to listen on the default HTTP port (port 80) and to serve the “Hello World!” message when the root URL is requested.
Step 3: Run the application
Press F5 to run the application. The application will start running on the Kestrel server and you should see the “Hello World!” message in your browser when you navigate to the root URL.
Conclusion
Kestrel is a lightweight, cross-platform web server that is optimized for running ASP.NET Core applications. It is fast, scalable, and secure, making it an ideal choice for building modern web applications. By understanding the architecture of Kestrel and its key features, you can build high-performance web applications that deliver a great user experience.
