Event

Event Triggers subscribe to a single event source. When the source produces an event (e.g., MQTT topic, OPC UA tag, or instance), the event enters the pipeline. If the source is invalid or does not generate events, the trigger goes into an error state.

The Event Trigger uses a Reference as its source. Path-based indexing is not supported. References must be static and cannot be dynamically driven by values or parameters. For more information, see References.

Event Trigger

Configuration

Reference

A reference to the source of the events. For example, this could be an MQTT input or an OPC UA tag. When the trigger references a template input, the event metadata includes a parameters object that defines all parameters associated with the source.

Output Mode

Determines whether the trigger should output the entire payload or only the attributes that have changed since the previous event.

All

Outputs the complete payload with each update. This is the default mode.

Example:

Initial event:

{
  "temperature": 75,
  "pressure": 100,
  "status": "running"
}

Next event (only temperature changed):

{
  "temperature": 76,
  "pressure": 100,
  "status": "running"
}

Compressed

Compares the payload to its previous value and only outputs attributes that have changed. This reduces bandwidth and simplifies downstream processing.

  • Only applies to complex payloads (objects)
  • Simple payloads (strings, numbers) are always output in full
  • The first event always includes the full payload

Example:

Initial event:

{
  "temperature": 75,
  "pressure": 100,
  "status": "running"
}

Next event (only temperature changed):

{
  "temperature": 76
}

Event Values

Value

{
  "attr1": "value of the event",
  "attr2": 2
}

Metadata

{
  "source": "Connection.internalBroker.pump({\"id\":\"3\"})",
  "parameters": {
    "id": "3"
  },
	"triggerType": ".TriggerEvent",
    "triggerName": "EventTrigger"
}

You can access a parameter in pipeline expressions using event.metadata.parameters.<parameterName> (for example, event.metadata.parameters.id).

Subscribable Sources

The following sources can be referenced by the Event Trigger:

Inputs

Individual inputs configured on connections can be subscribed to directly. The subscription behavior depends on the connection protocol and input type:

  • OPC UA Tags — Subscribe to individual tag value changes (OPC UA TCP)
  • OPC UA Events — Subscribe to OPC UA event notifications (OPC UA TCP)
  • OPC UA Branches — Subscribe to any tag change within the branch structure (OPC UA TCP)
  • OPC UA Collections — Subscribe to any tag change within the collection (OPC UA TCP)
  • MQTT Topics — Subscribe to messages on the topic (MQTT)
  • Sparkplug B Inputs — Subscribe to DATA, CMD, or RAW messages for the specified Group/Edge/Device (Sparkplug)
  • Azure IoT Hub Inputs — Subscribe to device messages (Microsoft Azure IoT Hub)
  • Azure Event Hub Inputs — Subscribe to event streams (Microsoft Azure Event Hubs)
  • Webhook Inputs — Subscribe to incoming HTTP requests (Webhook)
  • Ignition Path Inputs — Subscribe to tag value changes (Ignition Module)
  • Ignition UDT Inputs — Subscribe to UDT value changes (Ignition Module)

Instances

When an instance references one or more subscribable sources, you can subscribe to the instance directly. For detailed information on how instance subscriptions work, see Instance Subscriptions.

Subscription Behavior

Connection Recovery

Subscriptions automatically recover when connections are restored after a disconnect:

  • When a connection goes offline, subscriptions enter a waiting state
  • When the connection is re-established, subscriptions are automatically recreated
  • No manual intervention is required
  • For cached connections (OPC UA, Sparkplug B), the cache is refreshed after reconnection

Configuration Changes

If a subscribed source’s configuration changes, the subscription is automatically recreated with the new settings. This applies to:

  • Connection or Input setting modifications
  • Instance attribute changes
  • Namespace node modifications