OPC UA Connectors Disappearing From Systemlink Web User Interface

Updated Sep 13, 2024

Reported In

Software

  • SystemLink OPC UA Connector

Issue Details

The OPC UA connector in SystemLink Web user interface that I had configured disappeared after a recent SystemLink Server restart. What can I do to fix it?

Solution

The OPC UA Connector instances are read from databases when the service in SystemLink service starts. When the user interface requests the list of sessions, the service just looks at instances active in memory. The service does not re-query the database after initial startup.

With this in mind, and if there are nothing obviously wrong with the OPC Server that you are failing to see, there is a chance that the OPC Server was down when the SystemLink server restart happened, and that caused the issue for SystemLink to load the OPC UA connector instance as expected. Make sure that the OPC Server is running successfully before starting SystemLink.

Additional Information

If you are hosting the OPC server in the same machine as SystemLink server, you can run into a race condition if SystemLink services start before the OPC Server. In the long term you should consider hosting your OPC server in a different machine, however, if a temporary workaround is needed, you can restart your SystemLink Services after the machine has finished loading all services, or you can automate the workaround by switching NI SystemLink Service Manager (in Windows Services) from Automatic start to Automatic (Delayed start).

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