Building Production Backends with NestJS

Question

My focus for this month of October will be on NestJS framework and how it has imparted my development experience as a fullstack software engineer. NestJS provides a structured framework for building Node.js applications, but the framework alone does not determine whether an application will be maintainable in production.

The architecture surrounding the framework matters a lot. I will be sharing overview on my opinions when developing a secure and scalable systems in NestJS.

Feature-oriented modules

I prefer organizing backend systems around business capabilities rather than technical file types.

For example:

src/
├── modules/
│   ├── users/
│   ├── authentication/
│   ├── payments/
│   └── notifications/
│
├── infrastructure/
├── shared/
└── main.ts

This keeps related business functionality together.

Dependency boundaries

Business logic should not directly depend on infrastructure details.

For example, application code should depend on an abstraction:

export interface EmailSender {
  send(message: EmailMessage): Promise<void>;
}

rather than directly depending on a specific provider.

The infrastructure layer can then implement it:

export class ResendEmailSender implements EmailSender {
  async send(message: EmailMessage): Promise<void> {
    // provider implementation
  }
}

This makes it possible to replace infrastructure without rewriting business logic.

The goal

The goal is not to create the largest possible architecture.

The goal is to create a system where important decisions remain easy to change.

That principle becomes increasingly important as an application grows.