Forum Discussion
Azure AD connect in more than one DC
you can install Azure AD connect on another machine, but it must be in Staging mode. Azure AD connected cannot be running on 2 servers at the same time. There is not a great high availability story at this time. Any configuration changes you make on the operating instance need to be manually made on the staging instance. see https://docs.microsoft.com/en-us/azure/active-directory/connect/active-directory-aadconnectsync-operations for more details.
On a related note, the recommended best practice is to not put AAD connect on the DC. If you have an issue with AAD connect, you don't want it to affect the DC.
This was a quick and helpful response
You are welcome. edX has a good online class about this at https://courses.edx.org/courses/course-v1:Microsoft+CLD212.1x+3T2017/courseware/1d115a213d454e8387d74d3b7d345f25/d2639e4049d94ac9aace0fd16ddef434/?activate_block_id=block-v1%3AMicrosoft%2BCLD212.1x%2B3T2017%2Btype%40sequential%2Bblock%40d2639e4049d94ac9aace0fd16ddef434