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However as there will still be many existing clients which are only compatible with the MQTT Sparkplug™ B specification v2.2, we have made changes to MQTT Engine to establish a MQTT client whose only function is to publish the STATE message in its legacy format.

This is a configurable option and will be enabled disabled as default on a new installation of MQTT Engine.

How does this change in MQTT Engine affect me?

For most customers this change will be seamless and no additional configuration is required.

If you are updating from a previous version of MQTT Engine to v4.0.14, the configuration of the Legacy State template will be completed as part of the upgrade process and the Legacy Client enabled.

However, if using MQTT Distributor you will see that the tag [MQTT Distributor]Distributor Info/Connected Clients has increased by one. If you have scripting or an application using this tag value, then you will likely need to make the appropriate changes to accommodate this increase in the connected client count. 

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TahuClient    10Nov2022 17:13:31    ME-LS-6a6595d1-d44b-4: MQTT Client connected to tcp://localhost:1883 on thread Thread-2043
TahuClient    10Nov2022 17:13:31    ME-6ME-88477f61-7893-49b1: MQTT Client connected to tcp://localhost:1883 on thread Thread-2040

How do I configure

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the legacy state message?

The additional legacy STATE client is configured under the Advanced section for each of the configured MQTT servers in the MQTT Engine module configuration however for most customers there is no additional configuration required. The Legacy State template will be automatically populated with the variables from the server configuration Main and TLS sections

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if you are updating from a previous version of MQTT

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Engine to v4.0.14

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To disable, you simply deselect the Enable Legacy STATE messages option. To fully remove the retained legacy STATE message at the server, you will need to restart any connected server.