Implementing Microservices in NestJS Using MQTT

Introduction

Microservices architecture allows applications to be built as a collection of small, independent services that communicate over a network. In this guide, we demonstrate how to build NestJS microservices using MQTT as the communication protocol.

MQTT is a lightweight, publish–subscribe messaging protocol designed for real-time, event-driven systems. It is especially popular in IoT applications due to its low bandwidth usage and efficiency. Using MQTT for microservices enables fast, reliable, and asynchronous communication between services while keeping them loosely coupled and scalable.

What is MQTT?

MQTT (Message Queuing Telemetry Transport) is a lightweight, publish/subscribe messaging protocol designed for low-bandwidth, high-latency, or unreliable networks.

Why Use MQTT in Microservices?

MQTT offers several advantages when used as a microservice communication layer:

MQTT is not designed for heavy data streaming or durable message storage. For those use cases, Kafka is a better choice.

Why Use MQTT in Microservices?

In this tutorial, we will create four NestJS microservices that communicate via MQTT:

MQTT will act as a lightweight message broker, making it ideal for real-time, event-driven communication and IoT-style messaging between services.

Architecture Overview

Prerequisites

Step 1: Install NestJS CLI

npm i -g @nestjs/cli					

Choose npm or yarn and enable TypeScript.

Step 2: Create NestJS Applications

Step 3: Install MQTT Dependencies

Run this in ALL four projects:

npm install @nestjs/microservices mqtt					

Step 4: Install & Run MQTT Broker (Mosquitto)

C:\Program Files\mosquitto						

cd "C:\Program Files\mosquitto"
mosquitto.exe -v						

Step 5: Configure User Service (MQTT Subscriber)

Open user-service/src/main.ts

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import { Transport, MicroserviceOptions } from '@nestjs/microservices';

async function bootstrap() {
  const app = await NestFactory.createMicroservice<MicroserviceOptions>(
    AppModule,
    {
      transport: Transport.MQTT,
      options: {
        url: 'mqtt://localhost:1883',
      },
    },
  );
  await app.listen();
  console.log('User Service running with MQTT');
}
bootstrap();					

Open user-service/src/app.controller.ts

import { Controller } from '@nestjs/common';
import { MessagePattern } from '@nestjs/microservices';

@Controller()
export class AppController {

  @MessagePattern('get_users')
  handleGetUsers() {
    console.log('MQTT get_users received');
    return [
      { id: 1, name: 'Amit' },
      { id: 2, name: 'Rahul' },
    ];
  }
}					

MQTT topics replace REST routes in microservice communication.

Step 6: Configure Order Service

Open order-service/src/main.ts

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import { MicroserviceOptions, Transport } from '@nestjs/microservices';

async function bootstrap() {
  const app = await NestFactory.createMicroservice<MicroserviceOptions>(
    AppModule,
    {
      transport: Transport.MQTT,
      options: {
        url: 'mqtt://localhost:1883',
      },
    },
  );

  await app.listen();
  console.log('Order Service is running (MQTT)');
}
bootstrap();					

Open order-service/src/app.controller.ts

import { Controller } from '@nestjs/common';
import { MessagePattern } from '@nestjs/microservices';

@Controller()
export class AppController {

  @MessagePattern('get_orders')
  getOrders() {
    console.log('MQTT message received: get_orders');

    return [
      {
        id: 1,
        product: 'Laptop',
        price: 60000,
        status: 'PLACED',
      },
      {
        id: 2,
        product: 'Mobile',
        price: 25000,
        status: 'SHIPPED',
      },
    ];
  }
}					

Step 7: Configure Payment Service

Open payment-service/src/main.ts

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import { MicroserviceOptions, Transport } from '@nestjs/microservices';

async function bootstrap() {
  const app = await NestFactory.createMicroservice<MicroserviceOptions>(
    AppModule,
    {
      transport: Transport.MQTT,
      options: {
        url: 'mqtt://localhost:1883',
      },
    },
  );

  await app.listen();
  console.log('Payment Service is running (MQTT)');
}
bootstrap();					

Open payment-service/src/app.controller.ts

import { Controller } from '@nestjs/common';
import { MessagePattern } from '@nestjs/microservices';

@Controller()
export class AppController {

  @MessagePattern('get_payments')
  getPayments() {
    console.log('MQTT message received: get_payments');

    return [
      {
        id: 1,
        orderId: 1,
        amount: 60000,
        status: 'SUCCESS',
      },
      {
        id: 2,
        orderId: 2,
        amount: 25000,
        status: 'PENDING',
      },
    ];
  }
}					

Step 8: Configure API Gateway (MQTT Publisher)

Open api-gateway/src/app.module.ts

import { Module } from '@nestjs/common';
import { ClientsModule, Transport } from '@nestjs/microservices';
import { AppController } from './app.controller';

@Module({
  imports: [
    ClientsModule.register([
      {
        name: 'MQTT_SERVICE',
        transport: Transport.MQTT,
        options: {
          url: 'mqtt://localhost:1883',
        },
      },
    ]),
  ],
  controllers: [AppController],
})
export class AppModule {}					

Open api-gateway/src/app.controller.ts

import { Controller, Get, Inject } from '@nestjs/common';
import { ClientProxy } from '@nestjs/microservices';
import { firstValueFrom } from 'rxjs';

@Controller()
export class AppController {
  constructor(
    @Inject('MQTT_SERVICE') private readonly client: ClientProxy,
  ) {}

  @Get('users')
  getUsers() {
    return firstValueFrom(this.client.send('get_users', {}));
  }

  @Get('orders')
  getOrders() {
    return firstValueFrom(this.client.send('get_orders', {}));
  }

  @Get('payments')
  getPayments() {
    return firstValueFrom(this.client.send('get_payments', {}));
  }
}					

Step 9: Run the Applications

Start services in the following order:

# Start MQTT Broker

mosquitto

Step 10: Test in Browser

All responses are delivered via MQTT messaging and Now you will see data coming from the microservice, like.

#1 For User

#2 For Orders

#3 For Payments

Conclusion

MQTT is ideal for real-time, event-driven microservices and IoT-based systems.