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Creating alarms on MQTT tags is a simple process and is no different than creating alarms on any other Ignition tag (as documented here). However, there are some best practices that one should follow depending on the location of these MQTT tags and application specific use cases.

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The following two sections will provide details around the considerations above.

Alarm Configuration Persistence

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Deleting an MQTT Engine tag will result in a loss of alarm configuration. Deleting MQTT Engine tags can be required in certain cases. One example is if UDTs are being propagated from the Edge and the UDT definition on the Edge has been updated. This requires one to delete all instances of the UDT under MQTT Engine and delete the corresponding UDT definition so that it can be recreated/updated at MQTT Engine for the Edge side changes to take affect. There are two options for persisting alarm configuration in this case and they are as follows:

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Creating alarms on Ignition tags being consumed by MQTT Transmission on the Edge Gateway requires no special configuration; simply create the alarm on the desired tag as documented here.

Alarm Propagation

A common scenario beyond simply creating the alarm is propagating the alarm to the Central Gateway so it can be managed on the Edge, but present at both the Edge and Central Gateway. In Ignition 8, Cirrus Link MQTT modules used to allow for alarm configuration to be propagated from the Edge side tag to the MQTT Engine tag using the "Filtered Properties" feature. This is no longer possible as of MQTT modules version 4.0.6 due to potential timing issues around alarm evaluation at the Central Gateway that could result in incorrect evaluation. The recommended best practice for alarm propagation from the Edge to the Central Gateway is to use the Ignition Gateway Network to propagate alarms between gateways.