Hello all, I have a question I'm sure some folks have already addressed and hope there is a solution for my problem

I am in the process of migrating from an old single master --> multiple slave env 
running on OpenBSD 4.9 
openldap-server-2.4.23p2 - configured with slapd.conf

over to 4-master (regional) to 4 slaves (now - more to come regionally) 
running Ubuntu 16.04 and 
openldap 2.4.42 - configured with a cn=config database

I am trying to keep the environments in sync as we migrate dozens of different environments from the old slaves to the new slaves - which may take as long as 4 months :(

I started out by using slapcat to export the contents of the old server, then loading them into the new server.  I would originally drop all the data on the new servers and reload from the old.  

this is now no longer an option, as we migrate to the new servers, i cannot be dropping the entire database and replacing it with the new one - the time it takes to execute such a task creates an outage for users as well as applications that rely on the LDAP database.

So im looking for some guidance / options to keep my new LDAP environment in sync with my old, without any service disruptions on either set of systems.

Any help would be greatly appreciated!!