Q:

Redundant Subordinate/Issuing CA, How is the load balanced?

I'm tasked with implementing a 2 tier PKI (ADCS) with 2 subordinate CA's to provide high availabilty. Now I am wondering if I have 2 suborindates with the same certificate templates active, how will be determined what CA will handle requests. (No load balancers present)
Can I expect an even flow or will 1 CA be used most of the time?
The PKI will be built with Windows Server 2019

A:

[MS-WCCE] conforming clients (Windows and some 3rd party tools for other operating systems) select CA randomly. If you have two CAs with the same set of assigned certificate templates, both will have equal chances to get contacted by clients. If client is site-aware, the closest to client CA will be contacted, otherwise, random CA is selected.

