RabbitMQ/Krakend/NestJS - How can I post the consumed message through Krakend API's async agent?

This is my config for krakend.json

  "async_agent": [
    {
      "name": "test-agent",
      "connection": {
        "max_retries": 10,
        "backoff_strategy": "exponential-jitter"
      },
      "consumer": {
        "topic": "krakend",
        "workers": 5
      },
      "backend": [
        {
          "url_pattern": "/greeted",
          "method": "POST",
          "host": [ "http://127.0.0.1:2999" ],
          "disable_host_sanitize": false
        }
      ],
      "extra_config": {
        "async/amqp": {
          "host": "amqp://guest:guest@localhost:5672/",
          "name": "krakend",
          "exchange": "ApiGatewayExchange",
          "durable": true,
          "delete": false,
          "exclusive": false,
          "no_wait": false,
          "auto_ack": false
        }
      }
    }
  ]

Messages are sent from service-a like so:

export class AppService {
  constructor(@Inject('GREETING_SERVICE') private client: ClientProxy){}

  getHello(): ResponseDTO {
    const responseDTO: ResponseDTO = {
      action: 'Hello',
      service: 'from service A'
    }
    this.client.emit('', responseDTO);
    return responseDTO;
  }
}

And imported GREETING_SERVICE config like so:

  imports: [
    ClientsModule.register([
      {
        name: 'GREETING_SERVICE',
        transport: Transport.RMQ,
        options: {
          urls: ['amqp://test:test@localhost:5672/'],
          queue: 'krakend'
        }
      }
    ])
  ],

Lastly, this is the endpoint in another service (let's call this service-c) that gets that message from the consumer:

  @Post('greeted')
  TestHello(@Body() data: any) {
    console.log(data)
    return data
  }

The message is successfully consumed as set by the async_agent in my krakend file, but the message isn't posted as a body to that endpoint. When I did a console.log of that data supposedly passed, it just prints {}.

Am I doing anything wrong here? Been scratching my head for hours.

The async part of your krakend.json configuration looks good to me, but I am suspecting about the problem you might have.

Most of the javascript frameworks today will require you to pass specific headers to work their magic like Content-Type or Accept. You have to take into account that KrakenD will pass a very reduced set of headers to your NestJS application (Accept-Encoding and User-Agent as far as I can remember).

I am unfamiliar with NestJS, but I would bet that you need to pass the Content-Type and you are good to go. Here's my suggestion of configuration:

    "async_agent": [
        {
            "name": "test-agent",
            "connection": {
                "max_retries": 10,
                "backoff_strategy": "exponential-jitter"
            },
            "consumer": {
                "topic": "krakend",
                "workers": 5
            },
            "backend": [
                {
                    "url_pattern": "/greeted",
                    "method": "POST",
                    "host": [
                        "http://127.0.0.1:2999"
                    ],
                    "disable_host_sanitize": false,
                    "extra_config": {
                        "modifier/martian": {
                            "header.Modifier": {
                                "scope": [
                                    "request"
                                ],
                                "name": "Content-Type",
                                "value": "application/json"
                            }
                        }
                    }
                }
            ],
            "extra_config": {
                "async/amqp": {
                    "host": "amqp://guest:guest@localhost:5672/",
                    "name": "krakend",
                    "exchange": "ApiGatewayExchange",
                    "durable": true,
                    "delete": false,
                    "exclusive": false,
                    "no_wait": false,
                    "auto_ack": false
                }
            }
        }
    ]
}

Hope this helps