**Course Title:** Mastering NestJS: Building Scalable Server-Side Applications **Section Title:** Microservices with NestJS **Topic:** Develop a simple microservices application with NestJS and RabbitMQ for inter-service communication.(Lab topic) **Objective:** By the end of this topic, you will be able to design and implement a simple microservices application using NestJS and RabbitMQ for inter-service communication. You will learn how to create separate services, handle requests and responses, and use RabbitMQ as a message broker for communication between services. **Prerequisites:** * Basic understanding of NestJS and its architecture * Familiarity with RabbitMQ and message brokers * Knowledge of microservices architecture and design principles **Step 1: Setting up the Project Structure** Create a new NestJS project using the CLI: ```bash nest new microservices-app ``` Create separate folders for each service: ```bash mkdir services mkdir services/user mkdir services/product ``` **Step 2: Creating the User Service** In the `services/user/user.service.ts`, add the following code: ```typescript import { Injectable } from '@nestjs/common'; import { InjectRepository } from '@nestjs/typeorm'; import { Repository } from 'typeorm'; import { User } from './user.entity'; @Injectable() export class UserService { constructor( @InjectRepository(User) private readonly userRepository: Repository<User>, ) {} async createUser(user: User): Promise<User> { return this.userRepository.save(user); } async getUser(id: number): Promise<User> { return this.userRepository.findOne(id); } } ``` **Step 3: Creating the Product Service** In `services/product/product.service.ts`, add the following code: ```typescript import { Injectable } from '@nestjs/common'; import { InjectRepository } from '@nestjs/typeorm'; import { Repository } from 'typeorm'; import { Product } from './product.entity'; @Injectable() export class ProductService { constructor( @InjectRepository(Product) private readonly productRepository: Repository<Product>, ) {} async createProduct(product: Product): Promise<Product> { return this.productRepository.save(product); } async getProduct(id: number): Promise<Product> { return this.productRepository.findOne(id); } } ``` **Step 4: Setting up RabbitMQ** Install the `@nestjs/microservices` package: ```bash npm install @nestjs/microservices ``` Create a new file `rabbitmq.config.ts` with the following code: ```typescript import { MicroserviceOptions } from '@nestjs/microservices'; export const rabbitmqConfig: MicroserviceOptions = { transport: 'rabbitmq', options: { urls: ['amqp://localhost:5672'], queue: 'orders', }, }; ``` **Step 5: Creating the Order Service** In `services/order/order.service.ts`, add the following code: ```typescript import { Injectable } from '@nestjs/common'; import { InjectMicroservice } from '@nestjs/microservices'; import { MicroserviceOptions } from '@nestjs/microservices'; import { Observable } from 'rxjs'; import { User } from '../user/user.entity'; import { Product } from '../product/product.entity'; @Injectable() export class OrderService { constructor( @InjectMicroservice('RABBITMQ_SERVICE', rabbitmqConfig) private readonly rabbitmqService: any, ) {} async createOrder(user: User, product: Product): Promise<void> { const message = { user, product, }; await this.rabbitmqService.send('orders', message); } } ``` **Step 6: Creating the Order Controller** In `order.controller.ts`, add the following code: ```typescript import { Controller, Post, Body } from '@nestjs/common'; import { OrderService } from './order.service'; @Controller('orders') export class OrderController { constructor(private readonly orderService: OrderService) {} @Post() async createOrder(@Body() order: any): Promise<void> { await this.orderService.createOrder(order.user, order.product); } } ``` **Step 7: Running the Application** Start the NestJS application: ```bash npm run start ``` Use a tool like `rabbitmqadmin` to send a message to the `orders` queue: ```bash rabbitmqadmin declare queue name=orders rabbitmqadmin publish exchange=orders routing_key=orders body='{"user": {"id": 1, "name": "John Doe"}, "product": {"id": 1, "name": "Product 1"}}' ``` The order service will receive the message and create a new order. **Conclusion:** In this topic, you learned how to design and implement a simple microservices application using NestJS and RabbitMQ for inter-service communication. You created separate services, handled requests and responses, and used RabbitMQ as a message broker for communication between services. **Exercise:** Create a new service that consumes the order service and creates a new order in the database. **Additional Resources:** * RabbitMQ documentation: <https://www.rabbitmq.com/documentation.html> * NestJS documentation: <https://docs.nestjs.com/> **Leave a comment or ask for help if you have any questions or need further clarification on any of the steps.**