Integrating AWS Amplify with Eclipse Mosquitto for MQTT Messaging

Testing AWS Amplify's PubSub module against a local Eclipse Mosquitto broker before pointing it at AWS IoT Core.

Takahiro Iwasa

2020-04-25

2 min read

Eclipse Mosquitto can serve as a local MQTT broker for testing AWS Amplify’s PubSub module before pointing it at a managed endpoint like AWS IoT Core.

Setting Up Eclipse Mosquitto

Create a docker/docker-compose.yml file with the following content:

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version: '3.4'
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services:
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  mosquitto:
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    image: eclipse-mosquitto:1.6.9
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    ports:
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      - 1883:1883 # MQTT
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      - 9001:9001 # WebSocket
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    volumes:
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      - ./mosquitto:/mosquitto/config

Create a docker/mosquitto/mosquitto.conf file with the following content:

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listener 1883
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listener 9001
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protocol websockets

Start the Mosquitto container:

docker-compose up -d

Building Angular Application

Create a new Angular application and install the necessary dependencies:

ng new angular-mosquitto-sample
npm i --save [email protected] [email protected] [email protected]

Update src/polyfills.ts:

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/**
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 * ...
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 */
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/***************************************************************************************************
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 * APPLICATION IMPORTS
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 */
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// Add the following:
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(window as any).global = window;

Edit src/app/app.component.html:

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<h1>Received messages</h1>
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<hr/>
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<div *ngFor="let message of messages">
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  {{ message }}
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</div>

Edit src/app/app.component.ts:

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import { Component, OnInit } from '@angular/core';
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import { PubSub } from 'aws-amplify';
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import { MqttOverWSProvider } from '@aws-amplify/pubsub/lib/Providers';
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@Component({
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  selector: 'app-root',
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  templateUrl: './app.component.html',
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  styleUrls: ['./app.component.scss']
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})
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export class AppComponent implements OnInit {
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  messages = [];
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  ngOnInit() {
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    PubSub.addPluggable(new MqttOverWSProvider({
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      aws_pubsub_endpoint: 'ws://localhost:9001/',
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      // Do not use SSL
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      aws_appsync_dangerously_connect_to_http_endpoint_for_testing: true,
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    }));
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    PubSub.subscribe('test-topic').subscribe(payload => {
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      console.log(payload);
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      this.messages.push(payload.value.message);
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    });
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  }
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}

Testing the Application

Install mqtt with the following command:

npm i --save-dev mqtt

Publish MQTT messages to the local Mosquitto broker:

mqtt pub \
  -t 'test-topic' \
  -h localhost \
  -p 1883 \
  -m '{"message": "Hello World"}'

The Angular application should display the received message in real-time.

Conclusion

Running a local Mosquitto broker via docker-compose and wiring it into an Angular app through Amplify’s PubSub module made it possible to publish and receive MQTT messages end-to-end without any AWS IoT Core resources provisioned. Because PubSub talks to any MQTT-over-WebSocket broker through the same MqttOverWSProvider interface, the Angular side barely needs to know the difference — the polyfill for window.global and the PubSub.subscribe('test-topic') call stay the same whether the broker is Mosquitto on localhost:9001 or IoT Core. The one flag worth double-checking before moving past local testing is aws_appsync_dangerously_connect_to_http_endpoint_for_testing, since its name is a reasonably direct warning that it has no place in a production configuration.