What is Kestrel Web Server?

Riya
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Kestrel is the cross-platform web server that comes built-in with ASP.NET Core. It’s designed to:

Serve HTTP requests directly using managed code.
Run on Windows, Linux, and macOS .
Deliver high performance using asynchronous I/O .
Integrate seamlessly with reverse proxies such as IIS , Nginx , or Apache .

💡 Why Kestrel?
Before .NET Core, applications ran exclusively on IIS . But .NET Core’s goal was cross-platform flexibility — hence Kestrel became the default server for all ASP.NET Core applications.

⚙️ Architecture Overview

Kestrel uses:

Managed sockets (previously libuv for cross-platform I/O).
A highly optimized request/response pipeline built on top of System.IO.Pipelines .
Asynchronous task-based I/O for non-blocking performance.
Connection middleware to support protocols (HTTP/1.x, HTTP/2, and HTTP/3 with QUIC).

Kestrel can handle millions of concurrent requests efficiently — making it ideal for microservices , APIs , and real-time applicationss .