Communicating Between Quarkus and Mosquitto Containers: A Step-by-Step Guide

In today's post, we will explore how a Quarkus application can communicate with an Eclipse Mosquitto MQTT broker running in Docker containers. We will set up a simple application using Docker Compose, allowing for easy management of our services.

Prerequisites

Before we begin, ensure you have the following:

1. Docker Desktop installed on your machine.

2. A zip file of your Quarkus application, which we will unpack and build.

Project Structure

Let’s assume your Quarkus application zip file contains the following structure:

your-quarkus-app.zip
│
├── pom.xml
├── src
│   └── main
│       └── java
│           └── com
│               └── example
│                   └── YourApplication.java
└── application.properties

Step 1: Unpack and Build Your Quarkus Application

1. Unzip your Quarkus application:

    unzip your-quarkus-app.zip
    cd your-quarkus-app
   

2. Build your application using Maven:

    mvn clean package
   

This command generates a runnable JAR file in the target directory.

Step 2: Create the Docker Compose File

Next, create a docker-compose.yaml file in the root of your project directory:

version: '3.8'

services:
  pulsar-broker:
    image: eclipse-mosquitto:2
    container_name: pulsar-broker
    hostname: pulsar-broker
    ports:
      - "1884:1884"
    networks:
      - pulsar-network
    volumes:
      - ./mosquitto.conf:/mosquitto/config/mosquitto.conf

  quarkus-app:
    image: openjdk:17-jdk-alpine
    container_name: quarkus-app
    ports:
      - "8081:8080"
    environment:
      - MQTT_HOST=pulsar-broker
    networks:
      - pulsar-network
    volumes:
      - ./target/simple-mqtt-1.0.0-SNAPSHOT-runner.jar:/app/application.jar
      - ./target/application.properties:/app/config/application.properties
    command: >
      sh -c "sleep 30 && java -jar /app/application.jar"  # Add delay here
    working_dir: /app

networks:
  pulsar-network:
    external: true
    driver: bridge

Step 3: Create the Mosquitto Configuration File

Create a file named mosquitto.conf in the root of your project directory:

# Port on which Mosquitto will listen for connections
listener 1884

# Allow anonymous connections (no authentication required)
allow_anonymous true

bind_address 0.0.0.0

Step 4: Configure Your Quarkus Application

In your application.properties file, set up the MQTT configuration to connect to the Mosquitto broker:

# MQTT Receiving
mp.messaging.incoming.arconsis-twitch.connector=smallrye-mqtt
mp.messaging.incoming.arconsis-twitch.host=pulsar-broker
mp.messaging.incoming.arconsis-twitch.port=1884
mp.messaging.incoming.arconsis-twitch.topic=arconsis/twitch/#

mp.messaging.outgoing.hello-world.connector=smallrye-mqtt
mp.messaging.outgoing.hello-world.host=pulsar-broker
mp.messaging.outgoing.hello-world.port=1884
mp.messaging.outgoing.hello-world.topic=arconsis/twitch/hello-world

logging.level.io.smallrye.reactive.messaging.mqtt=DEBUG

Step 5: Start the Docker Containers

Run the following command to start the services defined in your Docker Compose file:

docker-compose up -d

This command will start both the Mosquitto broker and the Quarkus application in separate containers.

Step 6: Testing Your Quarkus Application

To test the endpoints of your Quarkus application running in the container, we’ve exposed port 8081 on your host machine. You can use Postman to make requests to your application.

1. Open Postman.

2. Set the request type to GET.

3. Enter the following URL:

    http://localhost:8081/hello/world/HellofromAdarsh
   

4. Click Send.

If everything is set up correctly, you should receive a response from your Quarkus application.

Conclusion

In this blog post, we explored how to set up a Quarkus application that communicates with an Eclipse Mosquitto MQTT broker using Docker containers. By leveraging Docker Compose, we simplified the management of our services and demonstrated how to expose and test our application endpoints.

Feel free to extend this setup to explore more complex interactions or deploy it in a production environment. Happy coding!