MQTT3

Detailed documentation on the MQTT3 pubsub component

Component format

To setup a MQTT3 pubsub create a component of type pubsub.mqtt3. See this guide on how to create and apply a pubsub configuration

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: mqtt-pubsub
spec:
  type: pubsub.mqtt3
  version: v1
  metadata:
    - name: url
      value: "tcp://[username][:password]@host.domain[:port]"
    # Optional
    - name: retain
      value: "false"
    - name: cleanSession
      value: "false"
    - name: qos
      value: "1"

Warning

The above example uses secrets as plain strings. It is recommended to use a secret store for the secrets as described here.

Spec metadata fields

Communication using TLS

To configure communication using TLS, ensure that the MQTT broker (e.g. emqx) is configured to support certificates and provide the caCert, clientCert, clientKey metadata in the component configuration. For example:

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: mqtt-pubsub
spec:
  type: pubsub.mqtt3
  version: v1
  metadata:
    - name: url
      value: "ssl://host.domain[:port]"
  # TLS configuration
    - name: caCert
      value: |
        -----BEGIN CERTIFICATE-----
        ...
        -----END CERTIFICATE-----        
    - name: clientCert
      value: |
        -----BEGIN CERTIFICATE-----
        ...
        -----END CERTIFICATE-----        
    - name: clientKey
      secretKeyRef:
        name: myMqttClientKey
        key: myMqttClientKey
    # Optional
    - name: retain
      value: "false"
    - name: cleanSession
      value: "false"
    - name: qos
      value: 1

Note that while the caCert and clientCert values may not be secrets, they can be referenced from a Dapr secret store as well for convenience.

Consuming a shared topic

When consuming a shared topic, each consumer must have a unique identifier. By default, the application ID is used to uniquely identify each consumer and publisher. In self-hosted mode, invoking each dapr run with a different application ID is sufficient to have them consume from the same shared topic. However, on Kubernetes, multiple instances of an application pod will share the same application ID, prohibiting all instances from consuming the same topic. To overcome this, configure the component’s consumerID metadata with a {uuid} tag (which will give each instance a randomly generated value on start up) or {podName} (which will use the Pod’s name on Kubernetes). For example:

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: mqtt-pubsub
spec:
  type: pubsub.mqtt3
  version: v1
  metadata:
    - name: consumerID
      value: "{uuid}"
    - name: cleanSession
      value: "true"
    - name: url
      value: "tcp://admin:public@localhost:1883"
    - name: qos
      value: 1
    - name: retain
      value: "false"

Warning

The above example uses secrets as plain strings. It is recommended to use a secret store for the secrets as described here.

Note that in the case, the value of the consumer ID is random every time Dapr restarts, so you should set cleanSession to true as well.

It is recommended to use StatefulSets with shared subscriptions.

Create a MQTT3 broker

• Self-Hosted
• Kubernetes

You can run a MQTT broker like emqx locally using Docker:

docker run -d -p 1883:1883 --name mqtt emqx:latest

You can then interact with the server using the client port: tcp://localhost:1883

You can run a MQTT3 broker in kubernetes using following yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: mqtt-broker
  labels:
    app-name: mqtt-broker
spec:
  replicas: 1
  selector:
    matchLabels:
      app-name: mqtt-broker
  template:
    metadata:
      labels:
        app-name: mqtt-broker
    spec:
      containers:
        - name: mqtt
          image: emqx:latest
          imagePullPolicy: IfNotPresent
          ports:
            - name: default
              containerPort: 1883
              protocol: TCP
---
apiVersion: v1
kind: Service
metadata:
  name: mqtt-broker
  labels:
    app-name: mqtt-broker
spec:
  type: ClusterIP
  selector:
    app-name: mqtt-broker
  ports:
    - port: 1883
      targetPort: default
      name: default
      protocol: TCP

You can then interact with the server using the client port: tcp://mqtt-broker.default.svc.cluster.local:1883

Related links

• Basic schema for a Dapr component
• Read this guide for instructions on configuring pub/sub components
• Pub/Sub building block

Last modified February 9, 2023: Subscribe with StatefulSet (25355f12)