Chapter 10. OPC UA Server196 PACSystems* RX7i & RX3i TCP/IP Ethernet Communications User Manual GFK-2224QOPC UA Automatic Restart FunctionThe OPC UA server generates the address space when it starts up. Thus, for a running OPC UA server, adding,deleting, or modifying a variable’s publish attribute requires that the server be restarted.The OPC UA server automatically restarts when you change a variable’s published state and return theapplication to a running state with logic equal. The server automatically restarts to assure that the latestpublished variables appear in the OPC UA address space. The server will also restart automatically for either astop-mode store or a run-mode store when the OPC UA server is currently running and the published variabletable is changed.In most cases, the time the server is offline due to the restart operation is relatively short. For run-mode storewith either a very large programs or significant changes, however, the time period can be extended while theserver restart waits for the controller to perform operations necessary to validate the program. Once theseoperations are complete, the server will return to operational status. If the current runtime status of the serveris needed, the SERVER_STATUS service request can be used.OPC UA Server CertificatesOPC UA client/server connections exchange digital certificates during the connection process. The OPC UAserver generates a self-signed certificate for the connection process. The OPC UA certificate includesapplication-specific information within the certificate. The application-specific information includes the TargetName and the controller’s TCP/IP address. Thus, if you change this information, the server certificate will notcontain this new information. This may cause certain clients to either not connect and/or generate warningmessages concerning the conflicts between the running OPC UA server and the information contained withinthe server certificate. If this information changes, the certificates should be cleared and regenerated.The OPC UA server certificates are stored internally on the controller’s non-volatile storage and are retainedthrough power cycles, clearing of memory and configuration from the programmer, and clearing of flashstorage from the programmer. The CONFIG_STATUS service request returns a bitmask to indicate if thecertificates exist on the target, or if they are currently cleared.If the OPC UA server is started with the certificates cleared, new certificates are generated during startup of theOPC UA server. If the OPC UA server is started with certificates already on the target, then those existingcertificates are used and new ones are not generated.If certificates currently exist on the target and need to be cleared, the OPC UA server must be stopped, andthen the CLEAR service request can be used to clear the certificates on the controller. When a CLEAR is used toclear the certificates, the certificates are permanently deleted and cannot be restored. Once this occurs, newcertificates must be generated. The CLEAR service request will not pass power if it is performed with the OPCUA server running.To assist with checking the status of and clearing certificates, the OPC UA subroutine previously discussedoffers a ClrSvr input that might be used to clear the server certificates any time the server is stopped.
