Develop NestJs microservices using Dapr pubsub and bindings.

Description

Dapr Module for Nest built on top of the Dapr JS SDK.

Installation

npm i --save @dbc-tech/nest-dapr

Requirements

Install Dapr as per getting started guide. Ensure Dapr is running with

dapr --version

Output:

CLI version: 1.7.1
Runtime version: 1.7.4

Quick start

The following scaffolds a Nest project with the nest-dapr package and demonstrates using Nest with Dapr using RabbitMQ pubsub & queue bindings.

Install Nest CLI

npm install -g @nestjs/cli

Scaffold Nest project

nest new nest-dapr
cd nest-dapr/

Install nest-dapr package

npm i --save @dbc-tech/nest-dapr

Import DaprModule in AppModule class

@Module({
  imports: [DaprModule.register()],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}

Import DaprClient from @dapr/dapr package and add dependency to AppController class

import { DaprClient } from '@dapr/dapr';
import { Controller, Get } from '@nestjs/common';
import { AppService } from './app.service';

@Controller()
export class AppController {
  constructor(
    private readonly appService: AppService,
    private readonly daprClient: DaprClient,
  ) {}

  @Get()
  getHello(): string {
    return this.appService.getHello();
  }
}

Create pubsub & topic names used for pubsub operations and message interface

const pubSubName = 'my-pubsub';
const topicName = 'my-topic';

interface Message {
  hello: string;
}

@Controller()

Create endpoint to publish topic message

@Post('pubsub')
async pubsub(): Promise<boolean> {
  const message: Message = { hello: 'world' };

  return this.daprClient.pubsub.publish(pubSubName, topicName, message);
}

Create pubsub handler which will subscribe to the topic and log the received message

@DaprPubSub(pubSubName, topicName)
pubSubHandler(message: Message): void {
  console.log(`Received topic:${topicName} message:`, message);
}

Create Dapr pubsub component in components folder

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: my-pubsub
  namespace: default
spec:
  type: pubsub.rabbitmq
  version: v1
  metadata:
  - name: host
    value: amqp://guest:guest@localhost:5674

Save file as components/rabbitmq-pubsub.yaml

Create docker-compose.yml in the project root used to run RabbitMQ

version: '3.9'
services:
  pubsub:
    image: rabbitmq:3-management-alpine
    ports:
      - 5674:5672
      - 15674:15672

Start RabbitMQ

docker-compose up

Create script to bootstrap your Nest project using Dapr sidecar. Update package.json and add script

"scripts": {
  ..
  "start:dapr": "dapr run --app-id nest-dapr --app-protocol http --app-port 50001 --dapr-http-port 50000 --components-path ./components npm run start"
},

Start Nest app with Dapr

npm run start:dapr

Invoke endpoint to publish the message

curl -X POST localhost:3000/pubsub

This should publish a message to RabbitMQ which should be consumed by the handler and written to the console:

== APP == Received topic:my-topic message: { hello: 'world' }

Full example

import { DaprClient } from '@dapr/dapr';
import { DaprPubSub } from '@dbc-tech/nest-dapr';
import { Controller, Get, Post } from '@nestjs/common';
import { AppService } from './app.service';

const pubSubName = 'my-pubsub';
const topicName = 'my-topic';

interface Message {
  hello: string;
}

@Controller()
export class AppController {
  constructor(
    private readonly appService: AppService,
    private readonly daprClient: DaprClient,
  ) {}

  @Get()
  getHello(): string {
    return this.appService.getHello();
  }

  @Post('pubsub')
  async pubsub(): Promise<boolean> {
    const message: Message = { hello: 'world' };

    return this.daprClient.pubsub.publish(pubSubName, topicName, message);
  }

  @DaprPubSub(pubSubName, topicName)
  pubSubHandler(message: Message): void {
    console.log(`Received topic:${topicName} message:`, message);
  }
}

DaprModule

DaprModule is a global Nest Module used to register DaprServer & DaprClient as providers within your project. It also registers all your handlers which listen to Dapr pubsub and input bindings so that when messages are received by Dapr, they are forwarded to the handler. Handler registration occurs during the onApplicationBootstrap lifecycle hook.

To use nest-dapr, import the DaprModule into the root AppModule and run the register() static method.

@Module({
  imports: [DaprModule.register()],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}

register() takes an optional DaprModuleOptions object which allows passing arguments to DaprServer instance.

export interface DaprModuleOptions {
  serverHost?: string;
  serverPort?: string;
  daprHost?: string;
  daprPort?: string;
  communicationProtocol?: CommunicationProtocolEnum;
  clientOptions?: DaprClientOptions;
}

See Dapr JS docs for more information about these arguments.

Async configuration

You can pass your options asynchronously instead of statically. In this case, use the registerAsync() method, which provides several ways to deal with async configuration. One of which is to use a factory function:

DaprModule.registerAsync({
  imports: [ConfigModule],
  useFactory: (configService: ConfigService) => ({
    serverHost: configService.get('DAPR_SERVER_HOST'),
    serverPort: configService.get('DAPR_SERVER_PORT'),
    daprHost: configService.get('DAPR_HOST'),
    daprPort: configService.get('DAPR_PORT'),
    communicationProtocol: CommunicationProtocolEnum.GRPC,
    clientOptions: {
      logger: {
        level: LogLevel.Verbose,
      },
    },
  }),
  inject: [ConfigService],
})

DaprServer & DaprClient providers

DaprModule registers DaprServer and DaprClient as Nest providers. These can be injected into your controllers and services like any other provider.

import { DaprClient } from '@dapr/dapr';
import { Controller, Post } from '@nestjs/common';

@Controller()
export class AppController {
  constructor(readonly daprClient: DaprClient) {}

  @Post()
  async pubsub(): Promise<boolean> {
    return this.daprClient.pubsub.publish('my-pub-sub', 'my-topic', {
      hello: 'world',
    });
  }
}

Dapr decorators

nest-dapr provides two TypeScript decorators which are used to declaratively configure subscriptions and bindings. These are used by DaprModule in conjunction with the handler method to define the handler implementations.

DaprPubSub decorator

DaprPubSub decorator is used to set-up a handler for receiving pubsub topic messages. The handler has 3 arguments (name, topicName & route). name specifies the pubsub component name as defined in the Dapr component metadata section. topicName is the name of the pubsub topic. Route is an optional argument and defines possible routing values.

Example:

@DaprPubSub('my-pubsub', 'my-topic')
pubSubHandler(message: any): void {
  console.log('Received message:', message);
}

RabbitMQ pubsub Component:

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: my-pubsub
  namespace: default
spec:
  type: pubsub.rabbitmq
  version: v1
  metadata:
  - name: host
    value: amqp://guest:guest@localhost:5674

Publish message:

await this.daprClient.pubsub.publish('my-pubsub', 'my-topic', { hello: 'world' });

In this example the handler pubSubHandler method will receive messages from the my-topic topic through the my-pubsub component which in this case is RabbitMQ.

DaprBinding decorator

DaprBinding decorator is used to set-up a handler for receiving input binding data. The handler has one argument name which specifies the binding component name as defined in the Dapr component metadata section.

Example:

@DaprBinding('my-queue-binding')
bindingHandler(message: any): void {
  coneole.log('Received message:', message);
}

RabbitMQ binding component:

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: my-queue-binding
  namespace: default
spec:
  type: bindings.rabbitmq
  version: v1
  metadata:
  - name: queueName
    value: queue1
  - name: host
    value: amqp://guest:guest@localhost:5674
  - name: durable
    value: true
  - name: deleteWhenUnused
    value: false
  - name: ttlInSeconds
    value: 60
  - name: prefetchCount
    value: 0
  - name: exclusive
    value: false
  - name: maxPriority
    value: 5
  - name: contentType
    value: "text/plain"

Send message:

await this.daprClient.binding.send('my-queue-binding', 'create', { hello: 'world' });

In this example the handler bindingHandler method will receive messages from the queue1 queue defined in the my-queue-binding component which in this case is RabbitMQ.

Writing handlers

DaprModule uses reflection to register all handlers found either in Controller or Provider classes. These classes must be registered in a Nest module. Providers must be decorated with the @Injectable() decorator at the class level. Once this is done and your provider is added to your module's [providers] array then nest-dapr will use Nest dependency injection container to resolve the provider instance and call your handler when the message is received.

Here's an example of a Provider containing a Dapr handler.

import { DaprPubSub } from '@dbc-tech/nest-dapr';
import { Injectable, Logger } from '@nestjs/common';

@Injectable()
export class AppService {
  private readonly logger = new Logger(AppService.name);

  @DaprPubSub('my-pubsub', 'my-topic')
  pubSubHandler(message: any): void {
    this.logger.log(`Received topic message:`, message);
  }
}

Examples

| Example | Description | |---|---| | Basics | Demonstrates pubsub & input binding using RabbitMQ |

Troubleshooting

Dapr is a complex set of tools and services and must be set-up and deployed carefully to ensure your system operates correctly. nest-dapr is merely syntactic sugar over the existing Dapr js-sdk. If things are not working out for you please review Dapr & SDK documentation and issues. Also please use one of the examples provided in this repo. They are updated and tested regularly and should work out of the box. If you find that both Dapr and the Javascript SDK is both working fine but nest-dapr is not working in some way, please file an issue and state clearly the problem and provide a reproducable code example. Filing an issue with something like: "It doesn't work" is likely to be ignored. Thank you.

Credits

Inspiration for this project is taken from dapr-nestjs-pubsub which I believe is the first attempt at integrating Dapr with Nest. Unfortunately this repo supports only pubsub messaging and I wanted to support input bindings as well. In the end I adopted the patterns established in Nest's own event-emitter repo and I pretty much borrowed all the metadata, reflection & decorator utils from there.

So full credit goes to the Nest development team :heart: