NestJS Best Practices

This lesson consolidates practical NestJS best practices used across production codebases—structure, validation, security, and testing discipline.

Architecture Practices

Organize by feature modules. Keep controllers thin, services focused, and persistence behind repositories. Prefer configuration and secrets outside code. Validate at the boundary with DTOs and ValidationPipe.

app.useGlobalPipes(new ValidationPipe({ whitelist: true, transform: true }));
app.useGlobalFilters(new AllExceptionsFilter());

Global validation and a consistent exception filter are baseline practices for almost every Nest API.

Practice Checklist

- Feature modules over technical-layer-only folders
- DTO validation on every external input
- Guards for authn/authz, not ad-hoc if checks
- Explicit module exports/imports
- Tests for services and critical e2e paths
- Config via ConfigModule + env validation

Use consistent naming: users.module.ts, users.service.ts, users.controller.ts.
Avoid circular dependencies; redesign or use forwardRef sparingly.
Document public API contracts and version breaking changes.
Log with request correlation ids.

Best Practices Cheatsheet

High-value Nest conventions.

Area	Practice
Structure	Feature modules
Input	DTO + ValidationPipe
Security	Guards + hashed secrets
Errors	HttpException + global filter
Data	Migrations, indexed queries
Tests	Unit + critical e2e

Security Basics

Enable Helmet (or Fastify equivalents), configure CORS explicitly, rate-limit auth routes, and never log tokens/passwords.

Modular Monolith First

Start modular in one deployable; extract Nest microservices only when ownership or scale demands it.

Common Mistakes

Anemic "utils" dumping ground instead of feature modules.
Business logic in controllers or guards.
Skipping validation because TypeScript types exist.
No tests on the payment/auth critical paths.

Key Takeaways

Feature modules, thin controllers, and validated DTOs are foundational.
Security and error handling should be consistent and centralized.
Config and secrets belong in the environment.
Test critical paths; measure before micro-optimizing.

Pro Tip

Treat each feature module as if it could become a package boundary later—even in a monolith, clear exports prevent spaghetti imports.