Microservice transports in NestJS - Mini Project: Build & Apply

Microservice transports

📖 Scenario: You are building a simple microservice system with NestJS. An API gateway receives HTTP requests and forwards them to a user microservice via TCP transport. The user microservice handles the business logic and returns results.

🎯 Goal: Set up a NestJS microservice with TCP transport, create message handlers, and connect a client from the API gateway to communicate with the microservice.

📋 What You'll Learn

Create a TCP microservice that listens on port 3001

Define a message handler using @MessagePattern

Register a ClientProxy in the API gateway module

Send messages from the gateway controller to the microservice

💡 Why This Matters

🌍 Real World

Microservice transports are the backbone of distributed NestJS applications, enabling services to communicate reliably across different deployment environments.

💼 Career

Understanding transport layers is essential for backend developers building scalable microservice architectures with NestJS.

1

Create the TCP microservice

In the user microservice's main.ts, create a NestJS microservice using Transport.TCP listening on host 0.0.0.0 and port 3001.

NestJS

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

async function bootstrap() {
  // Use createMicroservice with TCP transport on port 3001
  // Your code here
}
bootstrap();

Need a hint?

Use NestFactory.createMicroservice(AppModule, { transport: Transport.TCP, options: { host: '0.0.0.0', port: 3001 } }).

2

Create a message handler

In the user microservice controller, create a method getUser decorated with @MessagePattern({ cmd: 'get_user' }) that receives a data object with an id property and returns a user object with id and name.

NestJS

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

@Controller()
export class UsersController {
  // Add @MessagePattern with cmd 'get_user'
  // Return user object with id and name
  // Your code here
}

Need a hint?

Use @MessagePattern({ cmd: 'get_user' }) above your handler method.

3

Register ClientProxy in gateway module

In the API gateway's module, register a ClientsModule with a TCP client named USER_SERVICE that connects to the user microservice on localhost:3001.

NestJS

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

@Module({
  imports: [
    // Use ClientsModule.register with TCP transport
    // Name it 'USER_SERVICE' connecting to port 3001
    // Your code here
  ],
  controllers: [GatewayController],
})
export class GatewayModule {}

Need a hint?

Use ClientsModule.register([{ name: 'USER_SERVICE', transport: Transport.TCP, options: { host: 'localhost', port: 3001 } }]).

4

Send messages from gateway controller

In the gateway controller, inject the USER_SERVICE client using @Inject('USER_SERVICE') and create a GET endpoint /users/:id that sends a get_user message to the microservice with the user ID.

NestJS

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

@Controller('users')
export class GatewayController {
  // Inject USER_SERVICE client
  // Create GET endpoint that sends get_user message
  // Your code here
}

Need a hint?

Inject with @Inject('USER_SERVICE') private client: ClientProxy and send with this.client.send({ cmd: 'get_user' }, { id }).