Hi there,
Instance Scan, you got to love it 😁. It's one the most powerful features on the ServiceNow platform in my opinion. Okay, I'm a bit biased, being the person worldwide sharing most content on Instance Scan. A huge downside of Instance Scan is that you can only run one scan at the same time. Would a new scan be triggered (manually, scheduled, etcetera), it would simply throw an error message. Or... was! With the Zurich release this is resolved.
Let's have a closer look!
Pre-Zurich
The are several options to initiate a scan, for example manually or scheduled. What pre-Zurich was the case, that you could run only one scan at the same time. The scan engine is not designed (or opened up?) in such a way to handle multiple scans at the same time. Basically initiating a scan while there is already a current scan running, would throw an error message and abort starting the scan.
If you just started using Instance Scan, you're with a limited amount of admins and only initiating scans manually, this won't be an issue you would run into often. If utilizing Instance Scan to also initiate scans scheduled or for example automated when deploying changes, this will quickly become an issue.
Zurich... Queing of scans
The past few release, ServiceNow hardly developed on Instance Scan. Though with the Zurich release some improvements have been done. One of them, queuing of scans!
The queuing of scans starts with a new System Property "glide.scan.queue.enabled", which is (on Zurich EA) by default "true".
Like the new feature's name already reveals, if another scan is ongoing, any new scans initiated will be queued for execution. When initiating a new scan manually, a modal will presented displaying "The scan is in the queue".
Scan Queue
How the exact bits and pieces of Queuing of Scans works, I can't tell. The scripting behind this is not visible (or I need to search better?). What I can share is that any queued scans are visible in a new table called "Scan Queue" [scan_queue].
There's not much to mention about the fields on this new table. Amongst others you would see what the scan is about (Combo Id), the type of scan (Scan Type), and its status (Status).
Once the ongoing scan completes (successful or failed), the next scan in the Scan Queue starts executing automatically. If the same scan is initiated again, no duplicate will be created in the Scan Queue. Queue records are automatically deleted after they have finished.
Good to be aware of with new tables: for the Scan Queue Audit is turned on on the Collection Dictionary Entry, and also deletions will be captured.
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That's it. Hope this helps you utilize Instance Scan even better. If any questions or remarks, let me know!
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Kind regards,
Mark Roethof
Independent ServiceNow Consultant
10x ServiceNow MVP
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