Configure AppEngine redundancy

Important! Every redundant Application Server run-time node must be configured to use the System Management Server if data is being historized. Redundant nodes have an instance of HCAP running, which is used to synchronize tags and store-and-forward data between redundant AppEngines. With the release of System Platform 2023 R2, secure communication is required for HCAP, and thus, redundant nodes will not function without the SMS.

Data loss will occur if the SMS is not configured, and warnings and error messages will be generated.

See Common Platform for detailed instructions about SMS configuration.

The Primary/Backup AppEngines form a redundant pair. Application Server will generate the backup AppEngine automatically when redundancy is enabled for an AppEngine. Hierarchy of ApplicationObjects can only be assigned to the primary AppEngine. The primary and backup engines need to be assigned to redundancy enabled platforms, and they can be deployed separately.

For data acquisition, the Primary/Backup DIObjects (the data sources) must be separately created, configured, and deployed. Also, you must create, configure, and deploy a RedundantDIObject to control failovers between the two data source objects.

In a redundant system, install and configure the primary OPC server on the backup engine node.

When you configure redundancy, you configure the Primary object and the Backup object.

• Primary object: The main or central object that provides the functionality during run time. For AppEngines, this is the object you enable for redundancy. For data acquisition, this is the DIObject you intend to use first as your data source in run time.

• Backup object: The object that provides the functionality of the Primary object when the Primary object fails. For AppEngines, this is the object created by Application Server when the Primary object is enabled for redundancy. For data acquisition, this is the DIObject you do not intend to use first as your data source in the run-time.