How to Implement Microservices with NestJS

Introduction

NestJS is a progressive Node.js framework for building efficient, reliable, and scalable server-side applications using modern JavaScript or TypeScript. Leveraging the microservices architecture with NestJS allows developers to create an application that comprises small, loosely coupled services that communicate over well-defined APIs.

In this tutorial, we’ll explore how to set up and communicate between microservices using NestJS from the ground up. We will start by generating a new NestJS project, then break down different services, and finally ensure clear communication between those services using NestJS abilities.

Setting up a New NestJS Project

// Install the Nest CLI
npm i -g @nestjs/cli

// Create a new NestJS project
nest new project-name

After installation, we can jump right into code.

Creating Microservices in NestJS

// Create a new service in your project
nest generate service service-name

// Example for creating a 'users' service
nest generate service users

Each service in your NestJS application can act as a microservice, managing a particular aspect of your business logic.

Communication Between Microservices

Inter-service communication is a critical feature in a microservices architecture. NestJS provides a transport layer abstractions like TCP, Redis, and more. Here, we will use TCP for communication.

// In the main.ts file of each microservice, configure the microservice options
import { NestFactory } from '@nestjs/core';
import { MicroserviceOptions, Transport } from '@nestjs/microservices';
import { AppModule } from './app.module';

async function bootstrap() {
  const app = await NestFactory.createMicroservice<MicroserviceOptions>(AppModule, {
    transport: Transport.TCP,
    options: {
      host: 'localhost',
      port: 4000, // Use a unique port for each microservice
    },
  });
  app.listen();
}

bootstrap();

With the transport layer configured, the microservices can exchange messages.

Defining Patterns and Handlers

NestJS uses pattern-based message routing. You define a pattern, and NestJS binds it with a handler which is responsible for handling requests matching this pattern.

// Define a pattern in one microservice
@Controller()
export class AppController {
  @Post()
  async handle(@Body() data: any): Promise<any> {
    const pattern = { cmd: 'sum' };
    return this.clientProxy.send<number, number[]>(pattern, [data.a, data.b]);
  }
}

// Handle the pattern in another microservice
@UseGuards(obtainJwtGuard())
@Post()
public async getItem(@Query('id') id: string) {
  const pattern = { cmd: 'getItem' };
  return this.clientProxy.send<Item, string>(pattern, id);
}

This pattern and handler methodology allows you to create intricate communication logic between your services.

Exception Filters

NestJS allows you to create custom exception filters, making error handling across your microservices uniform and centralized.

@Catch()
export class AllExceptionsFilter implements ExceptionFilter {
  catch(exception: unknown, host: ArgumentsHost) {
      // Handle exceptions
  }
}

Handling exceptions is a significant part of developing a reliable microservices architecture.

Advanced Communication: Async Control Flows

For more complex scenarios, you may need to implement asynchronous control flows. This can involve different patterns like Sagas or CQRS (Command Query Responsibility Segregation).

// CQRS implementation pattern
@Module({
  imports: [CqrsModule],
  providers: [
    ItemCommandHandler,
    ItemQueryHandler,
    // Other command and query handlers
  ],
})
export class ItemsModule {}

The CQRS pattern can help you maintain high performance and scalability in systems with a high demand for read operations.

Conclusion

Implementing a microservices architecture with NestJS is not only manageable but powerful. Throughout this tutorial, we’ve explored several aspects, from setting up a project to intricate forms of service communications using the TCP transport and standing up to advanced patterns like CQRS. NestJS’s comprehensive toolkit streamlines microservice development to focus on building impactful business logic.