Overview

The Publish and Receive MQTT Messages node allows for sending and receiving metadata from the pipeline to a MQTT topic at a periodic interval or based on a trigger. This integration is useful for applications requiring real-time data exchange and monitoring.

Properties

Property	Description	Type	Default	Required
publish_topic	MQTT topic to publish to. Use Jinja2 template syntax to customize the topic using metadata.	string	null	No
publish_with_retain	If true, marks all published messages to be retained by MQTT broker.	bool	false	No
trigger_type	When to collect metadata. Options: Custom Trigger, Auto Trigger, Interval, Startup, Shutdown.	enum	auto_trigger	Yes
trigger	Send a MQTT message when this condition evaluates to true. Conditional on trigger_type being custom_trigger.	trigger-condition	null	No
interval	How frequently to send message. Set to 0 to publish every time metadata is collected.	number	0	Yes
format	Message Format. Options: JSON (Dynamic keys), JSON (Static keys), Custom Body.	enum	json	Yes
custom_body_template	Use Jinja2 template syntax to customize the body of the message. Conditional on format being custom_body.	text	"{}"	Yes
subscribe_topic	Comma separated list of MQTT topics to subscribe to. Use Jinja2 template syntax to customize the topic using metadata. Inserts metadata from topic into node metadata.	string	null	No
sanitize_messages	Replace invalid characters in topic name with underscores so you can use them in trigger conditions.	bool	true	No
persist_last_message	If true, retains latest message in node metadata for each topic.	bool	true	No
mqtt_protocol	MQTT Protocol. Options: MQTT, MQTT with SSL, MQTT over Websocket, MQTT over Websocket with SSL.	enum	mqtt	No
mqtt_host	MQTT Host.	string	null	Yes
mqtt_port	Port number to connect to. Leave blank to use default port based on MQTT Protocol.	string	null	No
username	Username.	string	null	No
password	Password.	string	null	No
validate_cert	Validate SSL Certificate?	bool	false	No
lastwill_message	Lastwill Message. Jinja2 template syntax to customize the message using metadata.	text	null	No
lastwill_topic	Use Jinja2 template syntax to customize the topic using metadata.	string	null	No
debug	Log Debug Messages?	bool	false	No

Template Syntax

custom_body_template, lastwill_message, lastwill_topic, publish_topic, and subscribe_topic uses Jinja2 Template Syntax for customizing the body of the MQTT message.

Variables available to the template:

Variable	Description
`meta`	Frame metadata. Contains keys like `nodes`, `objects`, and other custom metadata inserted by Custom function node.
`application_id`	The application ID of the deployment that produced this metadata.
`application_name`	The application name of the deployment that produced this metadata.
`deployment_id`	The deployment ID of the deployment that produced this metadata.
`deployment_name`	The deployment name of the deployment that produced this metadata.
`gateway_id`	The gateway ID of the deployment that produced this metadata.
`gateway_name`	The gateway name of the deployment that produced this metadata.

Example templates

Static text content:

Text content

Reference specific metadata:

{{ deployment_id }}

Metadata reinserted as is:

{{ meta | tojson }}

Output Metadata

Metadata Property	Description
topics	The MQTT topics subscribed to or published.
topics.	The specific MQTT topic being referenced.
topics..last_message	The last message received for a topic.
topics..messages	All messages received for a topic.
topics..topic_delta	Indicates if there has been a change in the topic.
topics.any_topic_delta	True if any topic has changed.
topics.all_topic_delta	True if all topics have changed.

Example JSON

{
    "nodes": {
        "mqtt1": {
            "type": "mqtt",
            "topics": {
                "topic1": {
                    "last_message": "message",
                    "messages": ["message"],
                    "topic_delta": true
                }
            },
            "any_topic_delta": true,
            "all_topic_delta": true
        }
    },
}