Writing Microservices using NestJS

~ Bhavin Patel ~ Leave a comment

nestjs-microservice-example series

Example code for nestjs microservice using REDIS
https://github.com/itsmebhavin/nestjs-microservice-example

Description

We are creating microservices using nestjs [nestjs.com] and REDIS. We have following components in our solution –

  • books-service (microservice)
  • magazines-service (microservice)
  • http-api (main entry point API for aggregating microservices)

How microservices are designed?

Books-Service (Microservice)

It’s basically a CRUD API for managing books. We have books object as below –

export class CreateBookDTO {
  readonly id: number;
  readonly title: string;
  readonly description: string;
  readonly author: string;
}

Registering Books-Service with REDIS

main.ts \\ Bootstraping

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

// Create new logger instance
const logger = new Logger('Main');

// Create micro service options
const microserviceOptions = {
  name: 'BOOK_SERVICE',
  transport: Transport.REDIS,
  options: {
    url: 'redis://localhost:6379',
  },
};
async function bootstrap() {
  const app = await NestFactory.createMicroservice(
    AppModule,
    microserviceOptions,
  );
  app.listen(() => {
    logger.log('Books microservice is listening ... ');
  });
}
bootstrap();

Controller methods for microservice

To add method which you want to expose as endpoint, you have to add @MessagePattern({ cmd: <endpoint-name>}) attribute.

 @MessagePattern({ cmd: 'getBooks' })
  async getBooks() {
    const books = await this.booksService.getBooks();
    return books;
  }

Registering Magazines-Service with REDIS

This is similar to books microservice registration / bootstraping. We have same types of CRUD endpoints in magazines controller.

Note: We are serving data from the mocks file. Mocks files are in respective microservice code. e.g. books.mocks.ts and magazines.mocks.ts.

How aggregator Client API is designed?

Our aggrator API is nothing but simple nestjs API application, so there is no changes in main.ts bootstrapping. But main change will be in controllers where we are going to call individual microservices.

Client API is going to communicate with Microservice using REDIS messaging channel.

REDIS setup

  • I have REDIS running in docker in my windows machine.
  • After that, I have installed Redis-cli for windows (x64).
  • I verified that Redis is working by running $#> redis-cli on command prompt.

Now that my REDIS is running, I can use it in aggregator api as Transport channel.

books.controller.ts

  client: ClientProxy;
  logger = new Logger('Books');
  constructor() {
    this.client = ClientProxyFactory.create({
      transport: Transport.REDIS,
      options: {
        url: 'redis://localhost:6379',
      },
    });
  }

How to use ClientProxy?

@Get()
  async getBooks() {
    this.logger.log('Getting all books');
    const pattern = { cmd: 'getBooks' };
    return await this.client.send(pattern, {});
  }

How to run whole eco-system?

  • Need to run books-microservice using npm run start:dev
  • Need to run magazines-microservice using npm run start:dev

finally, after you have both microservices are running, let’s start our aggregator api, so we can use it to build our client UI application.

  • Need to run http-api using npm run start:dev

Testing?

  • I got my aggregator api running on localhost:3000 and so i am using it in postman to test it.

Testing endpoints for books but same for magazines as well.

  1. GET localhost:3000\books
  2. GET localhost:3000\books\2
  3. POST localhost:3000\books
  {
    id: 8,
    title: 'Champak',
    description: 'Kids book for pre-k',
    author: 'John Barry',
  }
  • Author: Bhavin Patel
  • Todo: Work in progress to add Docker and kubernetes support.