ASP.NET Core Web Servers: Kestrel vs IIS Feature Comparison and Why You Need Both

The Kestrel web server is a new web server as part of ASP.NET Core. It is now the preferred web server for all new ASP.NET applications. In this article, we will review what it is, how to use it, and the differences between Kestrel vs IIS.

Why Do We Need the New Kestrel Web Server? What about IIS?

If you have been developing ASP.NET applications for a while, you are probably familiar with Internet Information Services (IIS). It does literally anything and everything as a web server. It is infinitely configurable with ASP.NET handlers & modules via the ASP.NET integrated pipeline. It has robust management APIs for configuration and deployment. It is even an FTP server.

The same codebase that has to support the original “.asp” pages from 15+ years ago now also handles new technologies like async ASP.NET. Like most software, as it ages it gets modified over time, they carry a lot of weight and bloat. IIS does everything, but it is not the fastest web server around. Lightweight web servers like Node.js and Netty make IIS look old and slow.

A Chance to Start Over

By creating the Kestrel web server, the .NET community was able to start over from scratch. They no longer had to worry about backward compatibility for technologies that were 15+ years old. They could take all of their past knowledge to build the simplest and fastest web server possible. That is exactly what they did. Kestrel and ASP.NET Core were built for speed.

Kestrel is more than just a new web server. ASP.NET Core & Kestrel combined are a whole new request pipeline for how ASP.NET requests work. Things like HTTP modules & handlers have been replaced with simple middleware. The entire System.Web namespace is gone. Another big advantage is designing a web server to take advantage of async from the ground up. Performance is now a feature of ASP.NET.

Built for Speed

One of the big problems with IIS and the existing ASP.NET pipeline was the performance of it. For most real world applications, the performance is perfectly fine. However, it lagged way behind in benchmarks. The combination of Kestrel & ASP.NET Core has been shown to be many times faster. It is great to see the team putting performance as a top priority.

Granted, benchmarking an ASP.NET request that says “hello world” is not comparable to most real applications that do multiple SQL queries, cache calls, and web service calls in a single request. ASP.NET makes it easy to do most I/O operations asynchronously. ASP.NET Core & Kestrel have been designed from the ground up to take advantage of async. Most real world apps should perform better if the developers follow good best practices around using async.

Cross Platform

If the goal was to get ASP.NET running on Linux, that meant porting IIS to Linux or making ASP.NET work without IIS. Kestrel solved this problem. As a developer, I can write my ASP.NET application and deploy it to Windows or Linux either one. Kestrel works as my web server on both. However, it is still recommended to use IIS, Apache, or NGINX as a reverse proxy in front of it. Next, we will discuss why that is.

Comparing Kestrel Web Server vs IIS

IIS does almost everything. Kestrel does as little as possible. Because of this, Kestrel is much faster but also lacks a lot of functionality. I would think of Kestrel as really more of an application server. It is recommended to use another web server in front of it for public web applications. Kestrel is designed to run ASP.NET as fast as possible. It relies on a full fledged web server to do deal with things like security, management, etc.

Microsoft suggests always using another web server in front of Kestrel for public websites.

 

 

Feature Comparison for Kestrel vs IIS

Here is an IIS vs Kestrel comparison of some key features. This should help you better understand the limitations of Kestrel. You can overcome these limitations by pairing it up with IIS or NGINX.

	IIS	Kestrel
Platform Support	Windows	Windows/Linux/Mac
Static Files	Yes	Yes
HTTP Access Logs	Yes	No
Port Sharing / Multiple apps*	Yes	No
SSL Certificates	Yes	Internal**
Windows Authentication	Yes	No
Management Console	Yes	No
Process Activation (start it up)	Yes	No
Application Initialization (warm it up)	Yes	No
Configuration API	Yes	No
Request Filtering & Limits	Yes	No
IP & Domain Restrictions	Yes	No
HTTP Redirect Rules	Yes	No
WebSocket Protocol	Yes	Middleware
Response Output Caching	Yes	No
Compression	Optional	Optional
FTP Server	Yes	No

* Port Sharing is a big limitation! This means you can’t host “site1.stackify.com” and “site2.stackify.com” both on port 80 on the same server, running different ASP.NET applications.

** Only works with internal SSL traffic between the reverse proxy web server and ASP.NET.

To learn more about ASP.NET server hosting technology, check out the Microsoft docs: Web server implementations in ASP.NET Core

Need help monitoring your ASP.NET Core applications?

Stackify Retrace’s APM solution works perfectly with ASP.NET Core!

Improve Your Code with Retrace APM

Stackify's APM tools are used by thousands of .NET, Java, PHP, Node.js, Python, & Ruby developers all over the world.
Explore Retrace's product features to learn more.

• App Performance Management
• Code Profiling
• Error Tracking
• Centralized Logging
• App & Server Metrics

Learn More

Author

mwatson

More articles by mwatson