MQTT

Detailed documentation on the MQTT pubsub component

Component format

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

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: mqtt-pubsub
  namespace: default
spec:
  type: pubsub.mqtt
  version: v1
  metadata:
  - name: url
    value: "tcp://[username][:password]@host.domain[:port]"
  - name: qos
    value: 1
  - name: retain
    value: "false"
  - name: cleanSession
    value: "true"
  - name: backOffMaxRetries
    value: "0"

Spec metadata fields

Field Required Details Example
url Y Address of the MQTT broker. Can be secretKeyRef to use a secret reference.
Use the tcp:// URI scheme for non-TLS communication.
Use the ssl:// URI scheme for TLS communication.
"tcp://[username][:password]@host.domain[:port]"
consumerID N The client ID used to connect to the MQTT broker. Defaults to the Dapr app ID. "myMqttClientApp"
qos N Indicates the Quality of Service Level (QoS) of the message. Defaults to 0. 1
retain N Defines whether the message is saved by the broker as the last known good value for a specified topic. Defaults to "false". "true", "false"
cleanSession N Sets the clean_session flag in the connection message to the MQTT broker if "true". Defaults to "true". "true", "false"
caCert Required for using TLS Certificate Authority (CA) certificate in PEM format for verifying server TLS certificates. "-----BEGIN CERTIFICATE-----\n<base64-encoded DER>\n-----END CERTIFICATE-----"
clientCert Required for using TLS TLS client certificate in PEM format. Must be used with clientKey. "-----BEGIN CERTIFICATE-----\n<base64-encoded DER>\n-----END CERTIFICATE-----"
clientKey Required for using TLS TLS client key in PEM format. Must be used with clientCert. Can be secretKeyRef to use a secret reference. "-----BEGIN RSA PRIVATE KEY-----\n<base64-encoded PKCS8>\n-----END RSA PRIVATE KEY-----"
backOffMaxRetries N The maximum number of retries to process the message before returning an error. Defaults to "0", which means that no retries will be attempted. "-1" can be specified to indicate that messages should be retried indefinitely until they are successfully processed or the application is shutdown. The component will wait 5 seconds between retries. "3"

Communication using TLS

To configure communication using TLS, ensure that the MQTT broker (e.g. mosquitto) 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
  namespace: default
spec:
  type: pubsub.mqtt
  version: v1
  metadata:
  - name: url
    value: "ssl://host.domain[:port]"
  - name: qos
    value: 1
  - name: retain
    value: "false"
  - name: cleanSession
    value: "false"
  - name: backoffMaxRetries
    value: "0"
  - name: caCert
    value: ${{ myLoadedCACert }}
  - name: clientCert
    value: ${{ myLoadedClientCert }}
  - name: clientKey
    secretKeyRef:
      name: myMqttClientKey
      key: myMqttClientKey
auth:
  secretStore: <SECRET_STORE_NAME>

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 consumerID value on start up. For example:

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: mqtt-pubsub
  namespace: default
spec:
  type: pubsub.mqtt
  version: v1
  metadata:
    - name: consumerID
      value: "{uuid}"
    - name: url
      value: "tcp://admin:public@localhost:1883"
    - name: qos
      value: 1
    - name: retain
      value: "false"
    - name: cleanSession
      value: "false"
    - name: backoffMaxRetries
      value: "0"

Create a MQTT broker


You can run a MQTT broker locally using Docker:

docker run -d -p 1883:1883 -p 9001:9001 --name mqtt eclipse-mosquitto:1.6.9

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


You can run a MQTT 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: eclipse-mosquitto:1.6.9
          imagePullPolicy: IfNotPresent
          ports:
            - name: default
              containerPort: 1883
              protocol: TCP
            - name: websocket
              containerPort: 9001
              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
    - port: 9001
      targetPort: websocket
      name: websocket
      protocol: TCP

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