FULL_STACK_DEVELOPER_2026_COMPLETE - Phase 04 Request Lifecycle, Routes and Decorators
Request Lifecycle, Routes and Decorators Trace an HTTP request through Fastify and Nest without hidden magic
Next.js NestJS + Fastify separate applications apps/web - already built apps/api - this phase
renders TaskFlow UI
Figure - Phase 04 keeps frontend and backend independent. They will communicate later in Phase 06.
FULL_STACK_DEVELOPER_2026_COMPLETE - Phase 04 Request Lifecycle, Routes and Decorators
Follow one request instead of memorizing decorators HTTP Client browser / curl / API tool
Fastify accepts socket + HTTP request
Nest Platform Adapter maps Fastify into Nest abstractions
Controller Route matches method + path
Provider / Service performs application work
Response serialized back to HTTP client
Figure - Phase 04 request lifecycle. Guards, pipes, interceptors, validation and database access are intentionally postponed to later phases.
Controller decorators form an HTTP routing boundary
apps/api/src/health/health.controller.ts
import { Controller, Get } from '@nestjs/common';
import { HealthService } from './health.service.js';@Controller('health')
export class HealthController {
constructor(private readonly healthService: HealthService) {}@Get()
getHealth() {
return this.healthService.getStatus();
}
}@Controller('health') establishes the route prefix. @Get() registers an HTTP GET handler at that prefix. The method name is for your code; the decorators determine the HTTP route.
Method and path are a pair Decorator Example route Meaning
@Get() GET /health Read a resource/status.@Post() POST /todos Create - introduced later.@Patch(':id') PATCH /todos/:id Partial update - introduced later.@Delete(':id') DELETE /todos/:id Delete - introduced later.FULL_STACK_DEVELOPER_2026_COMPLETE - Phase 04 Request Lifecycle, Routes and Decorators
Phase 05 will teach HTTP and REST in depth. Here we only need enough routing knowledge to understand how a request reaches a controller.
Return values become HTTP responses Controller/service return value return { status: 'ok', service: 'taskflow-api', };
Nest serializes ordinary JavaScript objects to JSON through the platform integration. Later phases add explicit status handling, DTO validation, exception filters and richer response behavior. Avoid solving future problems in Phase 04.
A controller should remain an HTTP boundary. Once business behavior becomes meaningful, delegate it to a service instead of putting database queries and rules directly inside route methods.
What is NOT in this lifecycle yet ● No validation pipe. ● No authentication guard. ● No authorization policy. ● No Prisma query. ● No interceptor-based logging architecture. ● No global exception strategy.
Those omissions are intentional. A clean mental model is easier to extend than a crowded diagram full of tools the learner has not earned yet.
Official source notes This phase is written against NestJS 12.0.3 and the Nest CLI 12.0.3 release line. Fastify remains on the stable v5 line; the September 17, 2026 stable patch reference is 5.12.5. The course does not adopt Fastify 6 alpha builds.
Primary references: docs.nestjs.com/modules, docs.nestjs.com/providers, docs.nestjs.com/techniques/performance, github.com/nestjs/nest/releases, github.com/nestjs/nest-cli/releases, github.com/fastify/fastify/releases.
Next.js is useful only when you can explain what runs on the server, what crosses into the browser, and which route owns a user-visible state.
Restate the goal of “Request Lifecycle Routes and Decorators” as one observable behavior. Write the success signal before touching code.
Trace the boundary map: route → Server Component → client boundary → request/data source → rendered UI. Mark the one boundary this lesson changes.
Inspect the current repository state and record the exact files, route, table, or runtime involved. Avoid creating an abstraction before you can name the existing owner.
Implement the smallest vertical slice. Add one coherent change, run the narrowest verification command, and read the output before continuing.
Connect the slice to TaskFlow’s phase artifact: A modular API with health endpoint and a small feature module whose controller and service responsibilities are separate.. Verify behavior from the outside as a user or API client would.
Create one controlled failure that is safe to reproduce. Predict the symptom first, capture evidence, locate the earliest broken boundary, then fix only that cause.
Close the reference and rebuild or explain the core change from memory. Record what you would monitor or test before trusting the same change in production.
// app/tasks/page.tsx
import { TaskList } from "./task-list";
export default async function TasksPage() {
const tasks = await loadTasks();
return <TaskList initialTasks={tasks} />;
}Do not copy this as a finished answer. Predict what each boundary does, type the smallest useful slice, run it, then compare the result with your prediction.
Locate the first browser-only API or stateful hook and move the client boundary to the smallest component that needs it.
Verify route params, fetch location, cache behavior, and the exact server response before changing JSX.
Without copying the final source, create a second small scenario that applies “Request Lifecycle Routes and Decorators” to a different TaskFlow resource or input. Write the acceptance criteria first, implement it, and provide the evidence that each criterion is satisfied.
Trace one request with logs through bootstrap, controller, and service.
Use the smallest change that demonstrates this lesson. Stop after it works and capture evidence.Provider not registered/exported/imported correctly
Predict the symptom before causing the failure. Then locate the earliest boundary where reality diverges from expectation.Why does this responsibility live here, what input does it trust, what output proves success, and what would go wrong if another layer owned it?
If your explanation is vague, repeat the boundary trace before moving on.Close the reference. Reproduce the core idea from memory or explain the exact request/data flow aloud. Then check your diff or notes for accidental shortcuts that bypass validation, authorization, error handling, or verification earned in earlier phases.