LABORATORY-NX-TCP

Note:
This project has to be compared to the LABORATORY-NX-NATS
https://github.com/JustalK/LABORATORY-NX-NATS

This project has been created using the libraries NX for creating a monorepository of microservices. Each microservices has been built with the CLI of NX as a Nest.js microservice. They communicate with the client using the TCP protocol and the message pattern of Nest.js.

Plan of the presentation

I explain with all the details how I build the project and my way of working.

• Development
• NX

Development

There are 3 apps:

• client: A nest.js client
• microservice1: A nest.js microservice on port 3001
• microservice2: A nest.js microservice on port 3002

When the api call one of the endpoint of the api, the service of the client is called. Inside the method, a message is sent to the microservices through the transporter TCP. Once the message is received, a response is sent back to the client as a response for the endpoint.

The communication is using the decentralized TCP transporter. A simple image for illustrating what is a decentralized communication:

Client

In the app.module.ts, we register the two microservices using the same transporter and port used in the microservices.

ClientsModule.register([
  {
    name: 'MICROSERVICE1',
    transport: Transport.TCP,
    options: {
        port: 3001,
    }
  },
  {
    name: 'MICROSERVICE2',
    transport: Transport.TCP,
    options: {
        port: 3002,
    }
  },
])

We inject our microservices using the ClientProxy inside our service app.service.ts with their respective name.

constructor(
  @Inject('MICROSERVICE1') private client1: ClientProxy,
  @Inject('MICROSERVICE2') private client2: ClientProxy
){}

For sending a message to a particular microservice, we can next using our injected variable.

// Example: sending a message 'greeting' with 'Micro1' as a parameter to microservice1
return this.client1.send({cmd: 'greeting'}, 'Micro1')

Microservices

Register, the app has a Nest.js microservice:

const app = await NestFactory.createMicroservice<MicroserviceOptions>(
  AppModule,
  {
    transport: Transport.TCP,
    options: {
      port: 3001
    }
  },
);

In the app.controler.ts, we use the decorator MessagePattern to indicate that a controller is waiting for a message from the client

@MessagePattern({cmd: 'greeting'})
getGreetingMessage(name: string): string {
  return `[MICROSERVICE 1] Hello ${name}`;
}

NX

Create a new application Nest

$ nx generate @nrwl/nest:application <Name of app/microservice>

Create a new service inside the app todos

$ nx generate @nrwl/nest:service <Name of service> --project <Name of Project> --directory app

Check the dependency graph

$ nx dep-graph

Run an application

$ nx serve <name of the app>
# Example
$ nx serve client

Run the app + microservices associated

$ nx run-many --parallel --target=serve --projects=client,microservice1,microservice2