AD Connect Connector is not changed to new Domain controller after swing migration

Question

I did same swing migration steps to upgrade the old AD connects for many of our tenants. Others have no issue but for 2 of the tenants I noticed below issue:

I have removed old AD connect from old server, then proceeded to demote the old Domain controller. Immediately Synchronization failed on the new AD connect in the new domain controller. That is when I noticed the Synchronization service manager in the new Domain controller AD connect is using the old Domain controller for connection and this connection failed with server down after demotion. Now I managed to get it working again by promoting back the Domain controller temporarily.

Don't know why this happened that the connection didn’t change to the new domain controller. Could you please advice on how I can now change this connection to connect from the new Domain controller?

Answer 1

It should find it automatically unless you have hard coded it.
https://vanhybrid.com/2016/01/25/force-azure-ad-connect-to-connect-to-specific-domain-controllers-only/#:~:text=Right%2Dclick%20the%20connector%20and%20choose%20Properties.&text=In%20the%20Configure%20Preferred%20DCs,OK%20to%20confirm%20the%20changes.

Verify that is not set to a specific one. If you continue to have issues, you could always set to the new DC to ensure its working for now.