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, which can then be shown on a dashboard, logged, used in a rule or read by 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	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.

All three components have Auto Connect on by default. The data format and the retry behaviour differ.

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	When the destination returns a status other than a success code, cannot be reached, or takes longer than 10 seconds to respond, makes up to three attempts in total, and if all three fail the batch is not retried further
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, included in the Server and Enterprise editions. Without it the components are unavailable. Refer to Licensing for what each edition includes.

Choosing between a publisher, a logger and a Tag Relay

A publisher sits in this category rather than with the loggers because 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 same trigger modes, either on a fixed interval or whenever a member tag's value changes, and neither starts until at least one collection is selected and every selected collection exists in the profile.