After upgrading to V12, the amount of time for Agents to connect after a system shutdown drastically increases, and can increase as a function of the number of Agents starting.
In the CP logs, you may see the following:
20201205/194839.396 - U00003413 Socket call 'connect(188.8.131.52, 8872)' returned error code '0'.
20201205/194839.396 - The operation completed successfully.
The Agent log for this would appear to have something similar to:
20201205/194839.396 - U02000012 Connection to Server 'AUTOMIC#CP001' denied.
20201205/194839.396 - U02000010 Connection to Server 'AUTOMIC:2217' terminated.
Release : 12.3
Component : AUTOMATION ENGINE
This is due to the Automic Automation Engine attempting to complete a service manager scan - the ports listed above would match service manager ports (default 8871). If the Automation Engine is unable to complete the scan, it will wait for a timeout which can slow down Agent onboarding.
This scan is controlled by the setting SMGR_AUTO_SCAN
To disable this functionality, set SMGR_AUTO_SCAN to N in UC_SYSTEM_SETTINGS within client 0.