Redundancy

This chapter deals with the case that the WinCC OA OPC UA server is running in a redundant WinCC OA system.

Redundancy in WinCC OA

If the WinCC OA system is redundant, then on each system a WinCC OA OPC UA server is running. The server shows in its server status the information whether it belongs to the active or to the passive system. Thereby the information is available for the client.

The process image is held consistently in both OPC UA servers. That means that the client receives from both servers the same values in case of queries as well as subscriptions. Value changes has to be sent either to both servers or to the active server by the client, as the OPC UA server on the passive system is not able to change values. If the client is sending the values only to the active server, value changes may get lost.

In order that the status data on the _OPCUAPvssServer data point can be different for both OPC UA servers in the redundant system, the OPC UA server on the second host uses automatically the _OPCUAPvssServer_2 data point.