MQTT Out

This is an enhanced version of the standard MQTT Out node, designed exclusively for FlowFuse users. The node features automatic configuration upon deployment when using within Flowfuse instance. The MQTT broker client is created automatically alongside the node configuration when added to the canvas.

Configuration Options

Server Configuration

The server is automatically configured and managed by the FlowFuse platform. All FlowFuse MQTT nodes within an instance share a single broker connection, ensuring efficient resource utilization and consistent connection management across all flows. Access control can be managed through the broker client management interface, where permissions for subscribe and publish operations can be configured.

Note: When the first node is added to the canvas, a new Team Broker User linked to the FlowFuse instance is automatically created. By default, this user has subscribe-only permissions.

Topic Configuration

Specify the default MQTT topic for message publication. This can be overridden at runtime by setting the msg.topic property in the input message.

Quality of Service

Select the QoS level for published messages:

  • Level 0: Fire and forget
  • Level 1: At least once
  • Level 2: Exactly once (default)

Retain Flag

Configure whether messages should be retained on the broker. The default value is false. Retained messages are delivered to new subscribers immediately upon subscription.

Message Input Properties

The following properties control message publication:

  • msg.payload: The message content to publish. JavaScript objects are automatically converted to JSON strings, while buffers are transmitted as binary data
  • msg.topic: Overrides the configured topic for this message
  • msg.qos: Overrides the configured quality of service level
  • msg.retain: Overrides the configured retain flag
  • msg.responseTopic: MQTT version 5 response topic for request-response patterns
  • msg.correlationData: MQTT version 5 correlation data for message tracking
  • msg.contentType: MQTT version 5 content type descriptor
  • msg.userProperties: MQTT version 5 custom user properties
  • msg.messageExpiryInterval: MQTT version 5 message expiry time in seconds
  • msg.topicAlias: MQTT version 5 topic alias for bandwidth optimization

Dynamic Control Operations

The node supports connection control through the msg.action property.

Connect

Establishes the broker connection.

msg.action = 'connect';

Disconnect

Terminates the connection.

msg.action = 'disconnect';

Note: When a control action is specified, the node performs that operation instead of publishing a message.

Publishing Messages

Basic Publishing

Send a message to the configured topic:

msg.payload = "Hello, MQTT!";
return msg;

Publishing to a Different Topic

Override the configured topic:

msg.topic = "sensors/temperature";
msg.payload = 25.5;
return msg;

Publishing with Custom QoS

Override the quality of service level:

msg.topic = "critical/alert";
msg.payload = "System warning";
msg.qos = 2; // Exactly once delivery
return msg;

Publishing Retained Messages

Publish a message that will be retained on the broker:

msg.topic = "sensors/last-known/temperature";
msg.payload = 25.5;
msg.retain = true;
return msg;

Publishing with MQTT v5 Properties

Use MQTT version 5 features:

msg.topic = "sensors/temperature";
msg.payload = { value: 25.5, unit: "celsius" };
msg.contentType = "application/json";
msg.messageExpiryInterval = 60; // Message expires in 60 seconds
msg.userProperties = {
  sensorId: "sensor-001",
  location: "warehouse"
};
return msg;

Version Support

This node fully supports MQTT version 5 features including response topics, correlation data, content types, user properties, message expiry intervals, and topic aliases. It maintains backward compatibility with earlier MQTT versions.