MQTT Trigger

Responds to changes in the specified topics. Returns the payload. In the properties dialog, you can configure the connection parameters for your MQTT query:

warning

If topics are connected multiple times via triggers in different connections, this may result in duplicate triggers for the individual connections.

This also applies to the use of wildcards.

The individual properties are:

Property	Description
Broker Connection	Select a configured broker connection from the drop-down menu.
Service Quality	Select how frequently the query should be executed.
Wait for Transfer	Select whether and how to wait for the transfer.
Payload Data Type	Select the data type: Byte Array or String.
Payload Encoding	Select the encoding for the MQTT query.
Topic	Enter the topic.

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Shared Subscriptions (MQTT v5)

MQTT Version 5 required

Shared Subscriptions are a feature of MQTT Version 5 and require support from both the broker and the client.

With Shared Subscriptions, multiple clients can join a shared consumer group and distribute incoming messages evenly among themselves. This enables horizontal scaling on the receiver side.

Topic Format

$shared/[groupName]/[topic]

Example:

$shared/inrayTest/SharedSubscriptionTest

Behavior

• Messages are distributed according to the round-robin principle or, depending on the broker, via “fair dispatch.” The goal is to distribute the load as evenly as possible among the clients within a group.
• Each published data record is delivered exactly once to a subscriber of the shared group (taking into account the respective QoS level).
• Clients with different groupName values receive messages independently of one another—each group operates in isolation.

Prerequisites

• Support for MQTT Version 5 by both the broker and the client.
• All participating clients must connect to the identical shared subscription topic (including the same groupName) to be part of the same consumer group.

QoS Behavior

Aspect	Description
QoS Support	QoS continues to be applied as usual (0, 1, or 2).
Impact on Distribution	The shared subscription affects only distribution, not the delivery guarantee.
Retry Attempts	If QoS > 0, depending on the broker implementation, delivery attempts may be repeated if a client does not acknowledge.

Limitations and Special Features

Aspect	Description
Message Order	The order is not guaranteed, as different clients process messages.
Stateful Processing	If states or order are relevant, they must be managed externally.
Broker Dependency	The exact behavior (e.g., distribution strategy) may vary depending on the MQTT broker.

Example

Publisher sends to:

SharedSubscriptionTest

Subscribers use:

$shared/inrayTest/SharedSubscriptionTest

With three active clients in the inrayTest group, incoming messages are distributed, e.g.:

Message	Delivered to
Message 1	Client A
Message 2	Client B
Message 3	Client C
Message 4	Client C