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Day 21Sprint 3 • ASP.NET Core Web API
2 Hours
Day 21: ASP.NET Core 9 Web APIs, Controllers & Kestrel Architecture
ASP.NET Core 9 is one of the world's fastest web frameworks, capable of serving over 7 million HTTP requests per second on the TechEmpower benchmarks. Its modular middleware pipeline and built-in Kestrel web server allow developers to build cloud-native REST APIs with enterprise reliability.
Understand how the .NET Kestrel HTTP server processes network requests
Learn the difference between Web API Controllers and Minimal APIs in .NET 9
Master the Dependency Injection container (AddTransient, AddScoped, AddSingleton)
Build your first RESTful Web API Controller returning JSON responses
Core Architectural Insights
- Kestrel is the cross-platform, asynchronous I/O HTTP web server built into .NET
- Middleware pipeline processes incoming HTTP requests in a sequential Russian-doll pattern
- Dependency Injection (DI) is natively built into the ASP.NET Core framework
- ApiController attribute automatically triggers model validation and returns HTTP 400 Bad Request on failure
Real-World Developer Analogy
Think of Kestrel as the security airport gate that receives all passengers (HTTP requests). The middleware pipeline is the series of security checkpoints (Authentication, Routing, CORS, Logging) that every passenger walks through before finally boarding the plane (your controller action).