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Primary Host Control

Overview​

Primary Host Control allows MQTT Engine to delay connecting to configured MQTT servers until one or more Ignition tags reach a specified state.

This feature is useful when MQTT Engine depends on other services or system conditions before it should begin processing MQTT data. For example, if a Central Gateway is running both MQTT Engine and Cloud Injectors, Primary Host Control can ensure MQTT Engine does not connect or publish its STATE message until all required services are online.

When configured, MQTT Engine evaluates the configured Primary Host Control tags every two seconds.

If all configured tags:

  • Have Good quality, and
  • Match their configured values,

MQTT Engine will:

  • Connect to its configured MQTT server(s).
  • Publish its Sparkplug STATE message.

If any control tag fails validation, MQTT Engine will disconnect from its MQTT server(s), or remain disconnected until the required conditions are met.

Version Availability ⚠️ Primary Host Control is available in MQTT Engine version 4.0.11 and later.

Configuration​

Primary Host Control is configured from the General tab of the MQTT Engine configuration.

Primary Host Control Tags​

Specify one or more Ignition tags that determine whether MQTT Engine should establish MQTT connections.

The configuration consists of a semicolon-separated list of tag definitions in the following format:

tagPath,dataType,expectedValue;
tagPath,dataType,expectedValue

For example:

[default]System/EngineReady,Boolean,true;[default]System/CloudReady,Boolean,true

MQTT Engine will connect only when every configured tag has Good quality and its current value matches the configured expected value.

Supported data types include:

  • Byte
  • Short
  • Integer
  • Long
  • Float
  • Double
  • Boolean
  • String