How to Check OPC UA Certificate Expiration and Get Expiry Alerts
OPC UA security relies on X.509 certificates for machine-to-machine authentication. When a certificate expires, OPC UA connections that depend on it fail, often producing connection errors that are not immediately obvious as certificate-related. Checking certificate expiration dates proactively and receiving advance notice before expiry are important maintenance practices for any OPC UA deployment that uses certificate-based security.
Where OPC UA Certificates Are Stored
OPC UA certificates are typically stored in a PKI (public key infrastructure) directory structure on the Windows file system, in a location configured by the OPC UA server or client application. The OPC UA specification defines a standard folder structure with subfolders for trusted certificates, rejected certificates, and certificate revocation lists. On Windows systems, you can navigate to the relevant folder and open any certificate file (.der or .pem format) using the Windows Certificate Viewer to see the validity period, including the expiration date. The OPC UA server’s configuration interface may also display certificate information directly if it includes a certificate management screen.
How OPC Expert Handles OPC UA Security
OPC Expert supports OPC UA security including certificate-based authentication and encrypted communication. When OPC Expert connects to an OPC UA server using a signed security mode, it manages its own client certificate and must trust the server’s certificate. The OPC Expert interface provides access to its certificate store, where you can view the certificates it manages and review their validity periods. If a certificate used by OPC Expert or by a connected OPC UA server is nearing expiration, the connection will fail once the expiration date passes. At that point, OPC Expert will report a connection error in its communication event window with details about the failure.
Automated Expiration Notification with Trigger OPC Events
OPC Expert does not include a dedicated certificate expiration calendar or a native certificate-specific alert scheduler. However, the Trigger OPC Events module can be configured to monitor OPC connection status and trigger an automated action, such as an email notification or script execution, when a connection fails or degrades. If a certificate expiry causes an OPC UA connection to drop, a trigger configured on that connection’s status tag would fire and send an alert. This is a reactive approach rather than a proactive one: it detects the failure rather than warning in advance of the expiration date. For proactive notification, the standard practice is to track certificate expiration dates in your organization’s change management or maintenance scheduling system and plan renewals before the expiration date is reached.
Best Practice: Certificate Renewal Scheduling
The most reliable approach to avoiding OPC UA certificate-related outages is to establish a certificate renewal schedule at the time each certificate is issued. OPC UA server certificates are commonly issued with validity periods of one to five years. Recording the expiration date in a maintenance management system and scheduling renewal work at least 30 days in advance provides sufficient lead time to generate, exchange, and trust the new certificate before the old one expires. For environments with many OPC UA connections, maintaining a simple spreadsheet of certificate expiration dates and reviewing it on a monthly basis is a low-overhead way to stay ahead of expiry events.
Relevant Tools
OPC Viewer from OPC Expert connects to OPC UA servers and displays real-time connection status including security negotiation errors that indicate certificate problems. Its communication event window provides detailed error messages that identify certificate-related failures specifically, which aids in diagnosing whether a connection issue is caused by an expired certificate or another security configuration problem. Trigger OPC Events from OPC Expert can be configured to send an email notification when any monitored OPC connection fails, providing reactive alerting for certificate expiry events and other connection interruptions.
Conclusion
Checking OPC UA certificate expiration requires navigating to the certificate store on the Windows file system or within the OPC UA server’s management interface. OPC Expert surfaces certificate-related connection errors in its communication event window and its Trigger OPC Events module can send automated alerts when a monitored connection fails. For proactive management, tracking certificate expiration dates in your maintenance scheduling system and planning renewals in advance remains the most reliable way to prevent certificate-related OPC UA outages.