Kestrel vs MediatR: What are the differences?

# Introduction

Kestrel and MediatR are two popular libraries in the .NET ecosystem that serve different purposes and have specific use cases. Here are the key differences between Kestrel and MediatR:

1. **Purpose**:
   Kestrel is a cross-platform web server that is used as the default web server in ASP.NET Core applications. It is optimized for handling HTTP requests and is designed for high performance. On the other hand, MediatR is a simple mediator pattern implementation for .NET that helps in implementing the mediator pattern in various applications. It helps in reducing the coupling between request handlers and the classes that send requests.

2. **Usage**:
   Kestrel is used to handle and process HTTP requests in web applications, acting as the entry point for all incoming requests. It is responsible for listening to network requests and passing them to the ASP.NET Core pipeline for processing. In contrast, MediatR is used for implementing the mediator pattern, where it acts as a middleman between classes that send requests and classes that handle those requests. It simplifies the flow of communication between objects by centralizing it through the mediator.

3. **Implementation**:
   Kestrel is a part of the ASP.NET Core ecosystem and is typically integrated into ASP.NET Core applications through the hosting process. It is configured and used alongside other components of the ASP.NET Core framework. On the other hand, MediatR is a standalone library that can be added to any .NET application without dependencies on specific frameworks. It provides a lightweight implementation of the mediator pattern that can be easily integrated into existing codebases.

4. **Concurrency**:
   Kestrel is optimized for handling a large number of concurrent connections efficiently. It utilizes asynchronous programming techniques to ensure that incoming requests are processed in a non-blocking manner, allowing for scalability in handling multiple requests simultaneously. In contrast, MediatR does not directly deal with concurrency in terms of handling incoming requests. It focuses more on simplifying the communication flow between components without concerns for parallel processing.

5. **Dependency Injection**:
   Kestrel does not provide direct support for dependency injection within its core functionality. Developers need to rely on the ASP.NET Core dependency injection container for injecting dependencies into various components of the application. On the other hand, MediatR integrates seamlessly with dependency injection containers in .NET applications, allowing for easy registration and resolution of dependencies required by request handlers and mediators.

6. **Extensibility**:
   Kestrel, being a web server, is primarily focused on handling HTTP requests and providing a platform for web application development. Its extensibility is centered around integrating with ASP.NET Core components and middleware for enhancing web server functionalities. On the other hand, MediatR is extensible in terms of adding custom behaviors, pipelines, and decorators to modify the request handling process. Developers can extend MediatR's capabilities through custom implementations to suit specific application requirements.

# In Summary, Kestrel and MediatR serve distinct purposes in the .NET ecosystem, with Kestrel focusing on web server functionality and performance optimization for handling HTTP requests, while MediatR simplifies communication between components through the mediator pattern implementation, offering flexibility and decoupling in application design.