Summary: A deep dive into how I structure backend services with NestJS for scalability, readability, and real-world performance in fintech and production systems.
As a backend engineer working in production systems, I’ve found that NestJS provides a powerful structure out of the box, but it’s still up to you to organize your services in a clean, scalable way.
In this post, I’ll walk you through how I build modular services with NestJS that are:
- Easy to maintain ✅
- Testable ✅
- Scalable across teams and features ✅
1. Use Feature-Based Folder Structure
Instead of separating code by type (controllers, services, models), I prefer feature-based organization:
/src
/payments
payment.controller.ts
payment.service.ts
payment.module.ts
/users
user.controller.ts
user.service.ts
user.module.ts
This structure makes it easier to scale horizontally and keep related files close together.
2. Split Business Logic Into Services (and Sub-Services)
Keep your controllers thin.
Keep your services focused.
If a service is doing too much, break it down further.
Example:
@Injectable()
export class PaymentService {
constructor(
private readonly transactionService: TransactionService,
private readonly walletService: WalletService,
) {}
async processPayment(...) {
await this.walletService.debit(...);
await this.transactionService.record(...);
}
}
3. Use Modules to Enforce Boundaries
NestJS modules help you control visibility and prevent accidental imports from unrelated parts of the app.
Export only what you want others to access:
@Module({
providers: [UserService],
exports: [UserService], // exposed to other modules
})
export class UserModule {}
4. Set Up Proper Dependency Injection (DI)
One of Nest’s biggest strengths is its DI system. You should:
Use constructor injection (not manual instantiation)
Keep dependencies explicit
Extract shared logic into utils or libs
5. Create a Shared Module for Common Logic
If multiple modules reuse the same service, guard, or pipe, move it into a SharedModule.
/shared
logging.interceptor.ts
current-user.decorator.ts
pagination.pipe.ts
Conclusion
NestJS gives you the tools, but clean architecture is still your job.
By sticking to modular structure, separating concerns, and using the DI system right, you can scale your codebase and your team with confidence.
Have you used NestJS in production? How do you structure your services?
Let’s swap notes 👇
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