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When building real-time applications or IoT services, integrating MQTT into your Dropwizard app can simplify messaging workflows. Let’s walk through how to configure MQTT in Dropwizard—using Docker for development and Kubernetes for production. We’ll touch on project setup, Docker setup, Dropwizard config files (config-dev.yml and config-prod.yml), and the environment-variable approach you’ll need in Kubernetes. Let’s dive in!

1. Add Required Dependencies

Start by updating your pom.xml to include essential libraries: 
<dependencies>
  <!-- Dropwizard core -->
  <dependency>
    <groupId>io.dropwizard</groupId>
    <artifactId>dropwizard-core</artifactId>
    <version>${dropwizard.version}</version>
  </dependency>

  <!-- Eclipse Paho MQTT client -->
  <dependency>
    <groupId>org.eclipse.paho</groupId>
    <artifactId>org.eclipse.paho.client.mqttv3</artifactId>
    <version>1.2.5</version>
  </dependency>

  <!-- Kubernetes client for env var integration -->
  <dependency>
    <groupId>io.fabric8</groupId>
    <artifactId>kubernetes-client</artifactId>
    <version>${fabric8.version}</version>
  </dependency>
</dependencies>
This gives you the MQTT client, Dropwizard framework, and optional Kubernetes support if you need more advanced interaction later.

2. Get MQTT Broker Running with Docker

For development, a simple Mosquitto container works great. Create a docker-compose.yml like this: 
version: '3.7'
services:
  mosquitto:
    image: eclipse-mosquitto
    ports:
      - "1883:1883"
      - "9001:9001"
Start it with: 
docker-compose up
It exposes MQTT on port 1883 and WebSockets on 9001. No credentials here—just free-flow messaging while you prototype.

3. Configure Dropwizard for Development

Create a config-dev.yml file: 
server:
  applicationConnectors:
    - type: http
      port: 8080

mqtt:
  brokerUrl: tcp://localhost:1883
  clientId: dev-client
  username: ""
  password: ""
  topic: test-topic
You'll also need a config class to load these values: 
public class MqttConfig {
  @JsonProperty
  public String brokerUrl;
  @JsonProperty
  public String clientId;
  @JsonProperty
  public String username;
  @JsonProperty
  public String password;
  @JsonProperty
  public String topic;
}
And then include it in your Dropwizard config: 
public class MyAppConfig extends Configuration {
  @JsonProperty
  public MqttConfig mqtt = new MqttConfig();
}
Within your application, use something like this to connect and publish: 
MqttClient client = new MqttClient(
    config.mqtt.brokerUrl,
    config.mqtt.clientId);
client.connect();
client.publish(config.mqtt.topic,
    new MqttMessage("Hello, MQTT!".getBytes()));
Launch locally with: 
java -jar target/myapp.jar server config-dev.yml
And’ve fun testing your MQTT setup on tcp://localhost:1883.

4. Prepare for Kubernetes Production

You’ll want to move MQTT credentials and broker endpoint into Kubernetes environment variables. This keeps sensitive information out of your code.
Generate Kubernetes resources:> 
kubectl create secret generic mqtt-secret \
  --from-literal=MQTT_USERNAME=produser \
  --from-literal=MQTT_PASSWORD=prodpass

kubectl create configmap mqtt-config \
  --from-literal=MQTT_BROKER_URL=tcp://mqtt-service:1883 \
  --from-literal=MQTT_TOPIC=prod-topic

5. Create Production Config File: config-prod.yml

This file will reference environment variables: 
server:
  applicationConnectors:
    - type: http
      port: 8080

mqtt:
  brokerUrl: ${MQTT_BROKER_URL}
  clientId: prod-client
  username: ${MQTT_USERNAME}
  password: ${MQTT_PASSWORD}
  topic: ${MQTT_TOPIC}
Running the app in Kubernetes, Dropwizard substitutes these environment variable values for real config.

6. Kubernetes Deployment Snippet

Make sure your Deployment includes these env vars: 
env:
  - name: MQTT_BROKER_URL
    valueFrom:
      configMapKeyRef:
        name: mqtt-config
        key: MQTT_BROKER_URL
  - name: MQTT_TOPIC
    valueFrom:
      configMapKeyRef:
        name: mqtt-config
        key: MQTT_TOPIC
  - name: MQTT_USERNAME
    valueFrom:
      secretKeyRef:
        name: mqtt-secret
        key: MQTT_USERNAME
  - name: MQTT_PASSWORD
    valueFrom:
      secretKeyRef:
        name: mqtt-secret
        key: MQTT_PASSWORD
Your container command would reference the prod config: 
java -jar myapp.jar server config-prod.yml

7. Why This Setup Works

  • Dev simplicity: Local Docker + YAML config = fast feedback loop.
  • Secure prod: No secrets in repos. Env vars from Kubernetes = safe and flexible.
  • Easy separation: Environment-specific YAML keeps dev/prod cleanly separated.
  • Scalable: Works great for a single broker today, and can be extended to MQTT clusters tomorrow.
By using Docker and Kubernetes for environment setup, and Dropwizard's YAML-based configuration, you create a robust, maintainable, and secure MQTT integration. Whether you're building IoT services or pushing live events, this setup gives you a solid foundation that scales from local testing to production deployment.
Your Dropwizard service can now send or receive MQTT messages confidently—whatever the environment, your configuration stays clear, clean, and under control.

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