Publishers and Subscribers

The Publishers & Subscribers category holds the components that move tag values between Profinity and other systems while both ends are running. A publisher pushes the current values of one or more profile tag collections to a receiver that is listening now. A subscriber brings data from an external source into the profile tag tree as ordinary read-only tags. You can show those tags on a dashboard, log them, use them in a rule or read them from a script.

Component	Direction	Connects to	Use it when
MQTT Publisher	Out of Profinity	A Message Queuing Telemetry Transport (MQTT) broker, in JSON or Sparkplug B format. Sparkplug B is an MQTT payload format for industrial data.	Other systems already subscribe to a broker for your data.
Webhook Publisher	Out of Profinity	An HTTP or HTTPS address, with an HTTP POST and a JSON payload	The consumer is an ordinary web service rather than a broker.
MQTT Subscriber	Into Profinity	A Sparkplug B namespace on an MQTT broker	The data comes from an external edge node, gateway, or industrial IoT platform.

For the Sparkplug messages and metric types that the MQTT Subscriber applies, refer to MQTT Subscriber Sparkplug behaviour.

All three components have Auto Connect on by default. The data format and the retry behaviour differ. The Webhook Publisher page lists what counts as a failed attempt.

Component	Selects data by	Data format	Retries
MQTT Publisher	Tag collections	JSON, a flat object of tag key to numeric value, or Sparkplug B	Keeps trying to connect every 5 seconds
Webhook Publisher	Tag collections	A JSON array of samples, in one POST for each publish	Makes up to three attempts for each publish, and does not retry a batch after the third failure
MQTT Subscriber	Topic filter	Sparkplug B metrics, scalar types only, written as read-only tags	Keeps trying to connect every 5 seconds

All three components require the Data Relay licensed feature. Refer to Licensing for the editions that include it.

Choosing between a publisher, a logger and a Tag Relay

A publisher pushes to a receiver that is listening now, whereas a logger writes to a file or database for later retrieval. To share tags between two Profinity instances, use Tag Relay instead, which has its own snapshot format and does not use Sparkplug.

The two publishers share the Logging mode setting, described in Logging modes. Neither starts until at least one collection is selected and every selected collection exists in the profile.