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Chapter 10. OPC UA Server
OPC UA Automatic Restart Function
The 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 the
application to a running state with logic equal. The server automatically restarts to assure that the latest
published variables appear in the OPC UA address space. The server will also restart automatically for either a
stop-mode store or a run-mode store when the OPC UA server is currently running and the published variable
table is changed.
In most cases, the time the server is offline due to the restart operation is relatively short. For run-mode store
with either a very large programs or significant changes, however, the time period can be extended while the
server restart waits for the controller to perform operations necessary to validate the program. Once these
operations are complete, the server will return to operational status. If the current runtime status of the server
is needed, the SERVER_STATUS service request can be used.
OPC UA Server Certificates
OPC UA client/server connections exchange digital certificates during the connection process. The OPC UA
server generates a self-signed certificate for the connection process. The OPC UA certificate includes
application-specific information within the certificate. The application-specific information includes the Target
Name and the controller's TCP/IP address. Thus, if you change this information, the server certificate will not
contain this new information. This may cause certain clients to either not connect and/or generate warning
messages concerning the conflicts between the running OPC UA server and the information contained within
the 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 retained
through power cycles, clearing of memory and configuration from the programmer, and clearing of flash
storage from the programmer. The CONFIG_STATUS service request returns a bitmask to indicate if the
certificates 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 the
OPC UA server. If the OPC UA server is started with certificates already on the target, then those existing
certificates 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, and
then the CLEAR service request can be used to clear the certificates on the controller. When a CLEAR is used to
clear the certificates, the certificates are permanently deleted and cannot be restored. Once this occurs, new
certificates must be generated. The CLEAR service request will not pass power if it is performed with the OPC
UA server running.
To assist with checking the status of and clearing certificates, the OPC UA subroutine previously discussed
offers a ClrSvr input that might be used to clear the server certificates any time the server is stopped.
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PACSystems* RX7i & RX3i TCP/IP Ethernet Communications User Manual
GFK-2224Q
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Troubleshooting
