The HTTP.sys driver (often referred to simply as HTTP.sys) is a web server for ASP.NET Core that only runs on Windows. It's a powerful and efficient component of the Windows operating system that handles HTTP requests in kernel mode, offering a robust alternative to other servers like Kestrel for specific deployment scenarios.
Understanding HTTP.sys
At its core, HTTP.sys acts as a high-performance HTTP request processor built into the Windows kernel. When an ASP.NET Core application is configured to use HTTP.sys, it directly leverages this kernel-mode driver to listen for and process incoming HTTP requests. This integration allows for a deep level of control and efficiency that user-mode web servers typically cannot achieve.
HTTP.sys serves as an alternative to the cross-platform Kestrel server and provides certain features that Kestrel does not directly offer, particularly those that capitalize on Windows-specific operating system capabilities.
Key Features and Benefits
Leveraging the Windows kernel, HTTP.sys brings several unique advantages and features to ASP.NET Core applications:
- Kernel-Mode Request Processing: By operating in kernel mode, HTTP.sys can process requests with lower overhead and higher throughput compared to user-mode servers.
- Port Sharing: Multiple applications can share the same IP address and port, simplifying server configuration and resource management.
- Integrated SSL Management: It offers built-in SSL (TLS) capabilities directly within the kernel, allowing for efficient certificate management and secure communication.
- Kernel-Mode Caching: HTTP.sys can cache static content directly in the kernel, significantly improving performance for frequently requested files.
- Direct Windows Authentication: It provides seamless integration with Windows Authentication, including NTLM and Kerberos, without requiring a reverse proxy.
- Reliability: As a core Windows component, it's designed for high availability and stability.
For more in-depth information, you can refer to the Microsoft documentation on HTTP.sys web server implementation for ASP.NET Core.
HTTP.sys vs. Kestrel
While both HTTP.sys and Kestrel can serve ASP.NET Core applications, they operate differently and are suited for distinct environments.
| Feature | HTTP.sys | Kestrel |
|---|---|---|
| Platform | Windows only | Cross-platform (Windows, Linux, macOS) |
| Location | Kernel-mode (leveraging the http.sys kernel driver) |
User-mode (application-level server) |
| Primary Use | Direct web server for ASP.NET Core on Windows, often self-hosted. | Primary web server for ASP.NET Core, often behind a reverse proxy. |
| Key Strengths | Port sharing, kernel-mode caching, integrated SSL, Windows Auth. | Lightweight, fast, highly configurable, excellent for microservices. |
| Deployment | Can be self-hosted directly without a reverse proxy on Windows. | Can be self-hosted directly; often deployed behind reverse proxies like IIS, Nginx, or Apache. |
| Features | Offers Windows-specific features that Kestrel doesn't provide. | Focuses on core HTTP handling, leaving advanced features to proxies. |
When to Use HTTP.sys
Choosing HTTP.sys for your ASP.NET Core application makes sense in several specific scenarios:
- Windows-Exclusive Deployments: If your application is guaranteed to only run on Windows servers, HTTP.sys can be a highly efficient choice.
- Advanced Windows Features: When you need to leverage features like kernel-mode port sharing, integrated Windows authentication, or kernel-mode caching directly from your web server.
- No Reverse Proxy Requirement: For simple deployments on Windows where you prefer not to use a separate reverse proxy (like IIS or Nginx) in front of your ASP.NET Core application, HTTP.sys can serve requests directly.
- Existing IIS Integration: Although Kestrel often runs behind IIS as a reverse proxy, HTTP.sys can sometimes offer tighter integration or an alternative for specific IIS-related features.
Practical Considerations
Implementing HTTP.sys in an ASP.NET Core application is straightforward. You typically configure it in your Program.cs file using the UseHttpSys() extension method on the web host builder:
public static IHostBuilder CreateHostBuilder(string[] args) =>
Host.CreateDefaultBuilder(args)
.ConfigureWebHostDefaults(webBuilder =>
{
webBuilder.UseStartup<Startup>();
webBuilder.UseHttpSys(options =>
{
// Optional: Configure HTTP.sys specific options
options.UrlPrefixes.Add("http://localhost:5000");
options.Authentication.Schemes = Microsoft.AspNetCore.Server.HttpSys.AuthenticationSchemes.Negotiate;
options.Authentication.AllowAnonymous = false;
});
});It's important to remember that using HTTP.sys limits your deployment options to Windows, which might be a critical factor for applications designed for cloud-native or cross-platform environments. For cross-platform compatibility, Kestrel combined with a reverse proxy remains the most common and flexible approach.
