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MQTT Publisher

The MQTT Publisher sends the current values of one or more profile tag collections to a Message Queuing Telemetry Transport (MQTT) broker, either on a fixed interval or whenever a member tag's value changes. Any system subscribed to the broker receives the data as it is published.

It sits in the Publishers & Subscribers category rather than Loggers because a publisher pushes to a subscriber that is listening now, whereas a logger writes to a file or database for later retrieval. To bring data from an external MQTT or Sparkplug source into Profinity instead, use the MQTT Subscriber.

flowchart LR
    subgraph Publishing["Publishing instance"]
        Tags --> Collections["Tag collections"] --> Publisher["MQTT Publisher"]
    end
    subgraph Server["MQTT server"]
        Broker["MQTT broker"]
    end
    subgraph Receiving["Receiving instance"]
        Subscriber["Subscriber"]
    end
    Publisher --> Broker --> Subscriber
The MQTT Publisher in the publishing instance sends tag collections to the broker on an MQTT server, on an interval or when a value changes, and the broker delivers them to every subscriber in the receiving instance

Licence required

The MQTT Publisher requires the Data Relay licensed feature, included in the Server and Enterprise editions. Without it the feature is unavailable. See Licensing for what each edition includes.

Quick start

Profinity does not run a broker, so you need one first: a self-hosted broker such as Mosquitto or HiveMQ, or a managed cloud MQTT service. These steps publish one collection as JSON.

  1. Add an MQTT Publisher to your profile from the Publishers & Subscribers category.
  2. Enter the broker address in Server URL, for example mqtt://broker.example.com:1883.
  3. Enter a Device ID that no other client on the broker uses.
  4. Leave Payload as JSON and enter a Destination Topic, for example profinity/site1/tags.
  5. Under Collections, add a collection and choose it by name, then save.

The publisher does not start until at least one collection is selected and every selected collection exists in the profile. With Auto Connect on, which is the default, it starts when the profile loads, and its status shows On while it is running. Subscribe to the topic on your broker to see the data arrive, in the form shown under Payload formats.

Settings

Connection settings

Setting Required Purpose
Server URL Yes The broker's connection URL, for example mqtt://broker.example.com:1883. The accepted schemes are mqtt, mqtts, http and https. Use mqtts:// to enable Transport Layer Security (TLS) and mqtt:// for an unencrypted connection. The port is taken from the URL, and when the URL has no port the publisher uses 1883 for mqtt:// and 8883 for mqtts://.
Trust all server certificates No Disables TLS server certificate validation for this connection. Enable only when connecting to a trusted broker using a self-signed certificate.
Username / Password No Credentials for broker authentication, when the broker requires them. The password is stored encrypted and can be left empty for username-only authentication.
Device ID Yes The MQTT client ID this publisher connects with, which must be unique among the clients connected to the broker. It is also used as the Sparkplug Edge Node ID when that field is left empty.
Payload No JSON publishes a flat object to the destination topic, and Sparkplug B publishes node birth, data, and death messages on Sparkplug topics. Defaults to JSON. See Payload formats.
Destination Topic Yes, for JSON The topic the flat JSON payload is published to, for example profinity/site1/tags. Shown only when Payload is JSON. A save without it fails with "You must provide a destination topic."

Sparkplug settings

Shown only when Payload is Sparkplug B:

Setting Required Purpose
Group ID Yes The Sparkplug group ID used in the topic path. A save without it fails with "You must provide a Sparkplug Group ID."
Edge Node ID No The Sparkplug edge node ID. Defaults to Device ID when left empty.

Publishing settings

Setting Default Purpose
Collections None The tag collections to publish. Add one or more, and choose each by name in the Collection field. An empty entry fails validation with "You must select a collection."
Auto Connect On Starts the publisher automatically when the profile is loaded.
Logging mode Snapshot Chooses between Snapshot, On Change and Everything. Refer to Logging modes for what each mode publishes.
Update Interval (Seconds) 10 From 1 to 86400 seconds. In Snapshot mode this is how often a full publish runs, and in On Change and Everything modes it is how often accumulated changes are sent.

Payload formats

JSON publishes a flat object of tag key to numeric value, with no timestamp, quality, or metadata alongside it. Each key is the tag path with every character other than a letter or digit replaced by an underscore, so Vehicles/Car1/Speed becomes the key Vehicles_Car1_Speed:

{
  "Vehicles_Car1_Speed": 87.4
}

A sample is included only when it has good quality and holds a finite number. The payload has no place for quality, so a tag that is stale, lost or not numeric does not appear in it.

Sparkplug B follows the Sparkplug topic and payload convention. The publisher sends a birth message (NBIRTH) on connect, data messages (NDATA) on each publish, and a death message (NDEATH) that the broker delivers if the connection drops unexpectedly. Topics take the form spBv1.0/{group}/NDATA/{edgeNode}. The publisher also subscribes to the node command topic and republishes its birth message when a Sparkplug-aware platform requests a rebirth. Sparkplug B is available on the MQTT Publisher only, not on the Webhook Publisher.

Status and troubleshooting

The MQTT Publisher shows On while it is running, Off when it is stopped, and Error when the connection to the broker fails or a publish fails. The status returns to On after the next successful publish.

The publisher keeps trying to connect every 5 seconds. A broker that is down when the publisher starts, or that goes away later, leaves the publisher in Error until the broker is back, and you do not need to restart the publisher. A rejected login is treated the same way, so fixing the credentials needs no restart either. The log records the reason once for each outage.

If the status shows Error, check the Logs for the underlying message, then confirm that:

  • The Server URL scheme and port match the broker.
  • The Username and Password are accepted.
  • No other client on the broker uses the same Device ID.
  • Trust all server certificates is on, if the broker has a self-signed certificate.

Changed in Profinity 2.3: the component was renamed from MQTT Logger, and existing MQTT Logger configurations keep working unchanged.

Rule actions can also send a one-off MQTT message or webhook, and need the Tag Rule Actions licensed feature. For a plain HTTP receiver, use the Webhook Publisher.