FULL_STACK_DEVELOPER_2026_COMPLETE - Phase 04 Exercises and Phase Exit
Exercises and Phase Exit Hands-on practice, debugging drills and the Phase 04 readiness standard
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 Exercises and Phase Exit
Hands-on lab - rebuild the mental model Do these exercises without jumping directly to the reference snapshot. The goal is to prove that you can reason from responsibilities rather than remember file names.
Level 1 - Follow 1 From the TaskFlow root, scaffold apps/api with Nest CLI 12.0.3 without nested Git or observability setup. 2 Run the generated application once before changing platforms. 3 Install @nestjs/platform-fastify 12.0.3, remove the Express platform package, and bootstrap Fastify on port 4000. 4 Create HealthModule, HealthController and HealthService. 5 Verify GET /health with Invoke-RestMethod. 6 Run the production build.
Level 2 - Modify Add a version field to the health response, for example version: "0.1.0". Decide whether the controller or service should own that returned application status object and explain your choice.
Level 3 - Implement Create a second lightweight route, GET /health/readiness, that returns a readiness object without copying the same object-building logic into multiple controller methods. Do not add database checks yet.
Level 4 - Engineer Imagine TaskFlow will later have Todos, Projects and Users. Sketch a module graph showing which feature modules AppModule should import. Do not create those files. Explain why creating all future modules now would be premature architecture.
Debugging drills Scenario Your task
HealthService removed from providers Predict the startup failure, then explain the dependency graph correction.
Port 4000 already occupied Find the owning process before choosing whether to stop it or change configuration.
HealthModule not imported Explain why files existing on disk do not make routes available.
@Controller('status') but request uses Identify the route mismatch without changing unrelated files. /health
Express-only example copied into Fastify Identify the platform assumption and find the Nest/Fastify equivalent. project
Oral architecture exam ● What is the difference between NestJS and Fastify? ● What does main.ts own? ● Why is AppModule called the root module? ● What information does @Module provide to Nest? ● Why can HealthController request HealthService without calling new HealthService()? ● Why does a provider file existing on disk not make it injectable automatically?
FULL_STACK_DEVELOPER_2026_COMPLETE - Phase 04 Exercises and Phase Exit
Phase 04 exit checklist ● [ ] apps/api is part of the existing pnpm monorepo. ● [ ] no nested .git exists under apps/api. ● [ ] Nest runs with Fastify on port 4000. ● [ ] GET /health returns status ok and service taskflow-api. ● [ ] you can explain modules, controllers, providers and DI without reading the code. ● [ ] you can locate and fix a missing provider registration. ● [ ] pnpm run build succeeds.
Now that the backend exists independently, the next phase studies the protocol it speaks: methods, URLs, headers, bodies, JSON, status codes, resources, idempotency and REST design. Only after that will Phase 06 connect Next.js to NestJS.
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.
NestJS structure becomes valuable when the request pipeline and responsibility of controllers, services, guards, pipes, and providers are explicit rather than magical.
Restate the goal of “Exercises and Phase Exit” as one observable behavior. Write the success signal before touching code.
Trace the boundary map: HTTP request → Fastify adapter → Nest pipeline → controller → service → response. 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.
@Controller("tasks")
export class TasksController {
constructor(private readonly tasks: TasksService) {}
@Get()
findAll() {
return this.tasks.findAll();
}
}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.
Read the constructor index in the error, then check provider registration, module imports, and exports in that order.
Confirm method/path, controller registration, global prefix, and guard/pipe behavior using request logs.
Without copying the final source, create a second small scenario that applies “Exercises and Phase Exit” to a different TaskFlow resource or input. Write the acceptance criteria first, implement it, and provide the evidence that each criterion is satisfied.
Inject the service through the constructor and explain how Nest resolves it.
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.