Request Lifecycle in Web Frameworks

Lessons

• The Anatomy of a Request · Request Lifecycle: How Web Frameworks Handle a Request
  Why users saw 504 errors while the application logged every request as successful, and how to align timeouts across load balancer, web server, app server and framework.
• PHP-FPM and the Shared-Nothing Model · Request Lifecycle: How Web Frameworks Handle a Request
  Why a PHP site returned 502 errors while CPU sat at 30%, how PHP-FPM workers serve requests, and what 'shared nothing' means for state between requests.
• WSGI, ASGI and the Event Loop · Request Lifecycle: How Web Frameworks Handle a Request
  Why one slow endpoint made every endpoint slow in an async service, and how WSGI workers, ASGI event loops and Node.js serve many requests at once.
• Laravel Octane and Long-Running Workers · Request Lifecycle: How Web Frameworks Handle a Request
  Why, after switching to Octane, a user briefly saw another customer's name, and which kinds of state leak between requests when the application stays in memory.
• The Laravel Request Lifecycle · Request Lifecycle: How Web Frameworks Handle a Request
  Why even the health-check endpoint took 120 ms, and how Laravel's bootstrap, service providers, middleware and terminate phase fit together.
• Symfony's HttpKernel and Kernel Events · Request Lifecycle: How Web Frameworks Handle a Request
  Why a maintenance-mode listener redirected visitors to the login page instead of showing a maintenance notice, and how Symfony's kernel events and listener priorities decide what runs first.
• The Django Request Lifecycle and Middleware Order · Request Lifecycle: How Web Frameworks Handle a Request
  Why an audit log recorded every action as 'anonymous', and how the order of MIDDLEWARE decides what each middleware can see.
• FastAPI and Starlette: Middleware, Exceptions and Dependencies · Request Lifecycle: How Web Frameworks Handle a Request
  Why an auth middleware that raised HTTPException(401) returned 500 errors, and how Starlette's middleware stack, exception handling and FastAPI dependencies are layered.
• Flask: Contexts, Hooks and Teardown · Request Lifecycle: How Web Frameworks Handle a Request
  Why a Flask app ran out of database connections after adding a header hook, and when before_request, after_request and teardown functions run.
• Express: The Middleware Stack and Error Handling · Request Lifecycle: How Web Frameworks Handle a Request
  Why requests to one endpoint hung until the client timed out, and how Express decides which middleware and error handlers run.
• NestJS: Middleware, Guards, Interceptors, Pipes and Filters · Request Lifecycle: How Web Frameworks Handle a Request
  Why mobile users got 403 errors from an ownership guard after a validation pipe was added, and the fixed order in which NestJS runs each part of its request pipeline.
• Next.js: Proxy (Middleware), Rendering and Caching · Request Lifecycle: How Web Frameworks Handle a Request
  Why a Next.js app made 40 session-API calls per page view, and what runs on each request: the proxy, route matching, server components, client components and caches.
• The Browser Side: React and Vue Page Loads · Request Lifecycle: How Web Frameworks Handle a Request
  Why a dashboard took four seconds to show data despite fast APIs, and what happens in the browser between navigation, rendering, hydration and data fetching in React and Vue apps.
• Choosing the Right Layer for Cross-Cutting Concerns · Request Lifecycle: How Web Frameworks Handle a Request
  Why one forgotten permission check exposed every customer's invoices, and how to place authentication, authorisation, validation, logging and transactions in the right layer of any framework.
• Spring Boot: Filters, DispatcherServlet and Interceptors · Request Lifecycle: How Web Frameworks Handle a Request
  Why expired tokens returned Spring Boot's default error JSON instead of the API's error format, and how a request moves through servlet filters, the DispatcherServlet, interceptors and controller advice.

Cookbook recipes

• Add JWT authentication to an Express API · Node.js
• Add request IDs and structured logs to FastAPI · FastAPI
• Protect routes in the Next.js App Router · Next.js
• Offload CPU-heavy work with worker threads · Node.js

Interview questions

Request Lifecycle in Web Frameworks interview questions and answers →