ASP.NET Core interview questions covering middleware & request pipeline.
Open a question for the full answer, code and interview guidance.
Middleware is software assembled into the ASP.NET Core HTTP request pipeline. Each middleware component can inspect or modify the incoming request, perform work before or after the next component, and inspect or modify the outgoing response.
When an HTTP request reaches an ASP.NET Core application, it passes through an ordered sequence of middleware components. Each component decides whether to call the next component in the pipeline.
Middleware order determines which components see a request and when they run. Incorrect ordering can cause authentication, authorization, routing, static files, CORS, or exception handling to behave incorrectly.
Use adds middleware that can call the next component in the pipeline. It is appropriate when processing should continue after the middleware performs its work.
Short-circuiting means a middleware produces a response without invoking the next middleware component.
Custom middleware is commonly implemented as a class with a constructor that receives RequestDelegate and an Invoke or InvokeAsync method that accepts HttpContext.
RequestDelegate represents a function that processes an HttpContext asynchronously. It is the fundamental delegate used to connect middleware components in the ASP.NET Core request pipeline.
HttpContext represents the current HTTP request and response. It provides access to Request, Response, User, Connection, Session when configured, Items, RequestServices, and other request-specific information.
HttpRequest contains information sent by the client, including the HTTP method, path, query string, headers, cookies, body, scheme, and host.
UseRouting adds endpoint routing middleware that matches the incoming request to an endpoint based on the application's route definitions and metadata.
Endpoint routing is the ASP.NET Core routing system that matches requests to executable endpoints. An endpoint can represent a controller action, Razor Page, minimal API handler, SignalR hub, health check, or other endpoint type.
UseStaticFiles enables the static file middleware, which serves files such as CSS, JavaScript, images, and fonts directly to clients.
UseHttpsRedirection redirects incoming HTTP requests to HTTPS. It helps ensure clients use an encrypted connection when HTTPS is available.
HTTP Strict Transport Security (HSTS) tells compatible browsers that a site should be accessed only over HTTPS for a specified period.
Exception handling middleware catches unhandled exceptions thrown by downstream components and converts them into an appropriate response.
The Developer Exception Page displays detailed information about unhandled exceptions, including stack traces and request-related diagnostic information.
Modern ASP.NET Core supports centralized exception handling through exception handling middleware and, in newer .NET versions, IExceptionHandler implementations.
Status code pages middleware can generate simple responses for HTTP error status codes that otherwise have no response body, such as 404 or 403 responses.
Response compression reduces the size of eligible HTTP responses before they are sent to clients. This can reduce bandwidth usage and improve transfer time for compressible content such as JSON, HTML, CSS, and JavaScript.
Response caching middleware implements HTTP caching behavior based on standard cache-related request and response headers.
Cross-Origin Resource Sharing (CORS) controls whether browser-based code from one origin is allowed to call resources hosted on another origin.
Authentication should normally run before authorization. Authentication establishes the current user identity, while authorization evaluates whether that user is allowed to access the selected resource.
A conventional middleware class can receive singleton-compatible dependencies through its constructor. Additional services can be injected into Invoke or InvokeAsync parameters, allowing scoped services to be resolved for the current request.
IMiddleware provides a factory-activated middleware model. A class implements IMiddleware and is registered with the dependency injection container. The framework resolves it through IMiddlewareFactory when the pipeline executes it.
Keep the pipeline intentional and easy to read. Place centralized exception handling early, serve static files before expensive application processing when appropriate, establish routing before middleware that relies on endpoint metadata, and run authentication before authorization.