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MQTT3 binding spec

Detailed documentation on the MQTT3 binding component

Component format

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

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: <NAME>
spec:
  type: bindings.mqtt3
  version: v1
  metadata:
    - name: url
      value: "tcp://[username][:password]@host.domain[:port]"
    - name: topic
      value: "mytopic"
    - name: consumerID
      value: "myapp"
    # Optional
    - name: retain
      value: "false"
    - name: cleanSession
      value: "false"
    - name: backOffMaxRetries
      value: "0"
    - name: direction
      value: "input, output"

Spec metadata fields

Field Required Binding support Details Example
url Y Input/Output 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]"
topic Y Input/Output The topic to listen on or send events to. "mytopic"
consumerID Y Input/Output The client ID used to connect to the MQTT broker. "myMqttClientApp"
retain N Input/Output 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 Input/Output Sets the clean_session flag in the connection message to the MQTT broker if "true". Defaults to "false". "true", "false"
caCert Required for using TLS Input/Output Certificate Authority (CA) certificate in PEM format for verifying server TLS certificates. See example below
clientCert Required for using TLS Input/Output TLS client certificate in PEM format. Must be used with clientKey. See example below
clientKey Required for using TLS Input/Output TLS client key in PEM format. Must be used with clientCert. Can be secretKeyRef to use a secret reference. See example below
backOffMaxRetries N Input 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"
direction N Input/Output The direction of the binding "input", "output", "input, output"

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-binding
spec:
  type: bindings.mqtt3
  version: v1
  metadata:
    - name: url
      value: "ssl://host.domain[:port]"
    - name: topic
      value: "topic1"
    - name: consumerID
      value: "myapp"
    # 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: backoffMaxRetries
      value: "0"

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. If running multiple instances of an application, you 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-binding
  namespace: default
spec:
  type: bindings.mqtt3
  version: v1
  metadata:
  - name: consumerID
    value: "{uuid}"
  - name: url
    value: "tcp://admin:public@localhost:1883"
  - name: topic
    value: "topic1"
  - name: retain
    value: "false"
  - name: cleanSession
    value: "true"
  - name: backoffMaxRetries
    value: "0"

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

Binding support

This component supports both input and output binding interfaces.

This component supports output binding with the following operations:

  • create: publishes a new message

Set topic per-request

You can override the topic in component metadata on a per-request basis:

{
  "operation": "create",
  "metadata": {
    "topic": "myTopic"
  },
  "data": "<h1>Testing Dapr Bindings</h1>This is a test.<br>Bye!"
}

Set retain property per-request

You can override the retain property in component metadata on a per-request basis:

{
  "operation": "create",
  "metadata": {
    "retain": "true"
  },
  "data": "<h1>Testing Dapr Bindings</h1>This is a test.<br>Bye!"
}

Last modified July 31, 2023: [Bindings] Update specs to include `direction` (#3646) (e33f5a95)