I’m here to explain, in simple terms, the difference between the HTTP Request Lifecycle in the old ASP.NET Framework versus the new ASP.NET Core, and the major changes that have happened in the Pipeline from then until now.

This explanation will help you understand how requests flow through the system and why ASP.NET Core has become the superior choice for developers today.

1. HTTP Request Lifecycle in the Legacy Version (ASP.NET Framework)

When a client sends a request (e.g., /Employee/GetAll), the following happens:

1. Receiving the Request: The Web Server (IIS) receives the request first. The entire pipeline lives inside IIS, not within the Web Application itself.

2. Entering the Pipeline: The request carries two separate entities: HttpRequest and HttpResponse, both tied to a massive object called System.Web.HttpContext.

   • The Problem: This Context is "heavy"—it carries a lot of data and overhead that the application might not even need.

3. Passing through Modules: The request must pass through every registered Module, regardless of how many there are. There is no real flexibility in controlling their order easily.

4. Routing: It reaches the Routing Module to extract the Controller Name and Action Name.

5. Selecting the Controller/Action: It hits the MapControllerRoute which directs the request to the appropriate Controller and Action.

6. Execution (Based on App Type):

   • If MVC: Fetch data → Fill ViewModel/Model → Send Model to View → Render View inside Layout → Generate final HTML → Return HTML as Response.

   • If Web API: Fetch data → Fill DTO/Model → Convert result to JSON → Return JSON Response.

7. The Response travels back through the pipeline and finally reaches the browser.

❌ Disadvantages of the Legacy Version:

• IIS Dependent: Not Cross-Platform (Windows only).

• Heavy HttpContext: Very difficult to Unit Test.

• Rigid Pipeline: Not flexible or modular.

• Lower Performance: Higher memory consumption and slower execution.

• Complex Architecture: Heavy and tightly coupled.

2. HTTP Request Lifecycle in the New Version (ASP.NET Core)

1. Receiving the Request: The Web Server (Kestrel or IIS) receives the request and passes it directly into the application itself.

   • The Big Difference: The Pipeline is now inside the Application, and you have full control over the order of every Middleware.

2. Entering the Pipeline (Program.cs): The pipeline is modular and built step-by-step.

3. New HttpContext: The request travels with a single, lightweight HttpContext. It contains the HttpRequest and HttpResponse in a clean, optimized structure.

4. Passing through Middlewares (By Choice): You define exactly which Middleware runs and in what order. You can easily add or remove components.

5. Reaching the Controller/Action: The standard steps follow: Get Data → Fill Model → Render View or Return JSON.

6. The Response flows back through the Middlewares in reverse order to reach the browser.

✔ Advantages of the New Version:

• Cross-Platform: Runs on Linux, Windows, and macOS.

• Lightweight HttpContext: Very easy to mock and Unit Test.

• Flexible & Modular Pipeline: You decide the Middleware order.

• High Performance: Faster and uses significantly less memory.

• Clean & Modern Architecture: Perfectly suited for Cloud Apps and Microservices.

The Bottom Line 🎯

The fundamental shift is that ASP.NET Core provides:

• A Flexible, Modular Pipeline that is easy to control.

• A Lightweight Context that is test-friendly.

• Higher performance and a modern, Cross-platform foundation.

In short, if you want faster, flexible, scalable, and easily testable applications, ASP.NET Core is the definitive choice for modern developers.