Complications migrating from Snow Leopard Server to Mountain Lion Server.

Question

I'm migrating from Snow Leopard Server to Mountain Lion Server. The article "OS X Server: Upgrade and migration" (http://support.apple.com/kb/HT5381) says
"Make sure that any DNS or DHCP servers on which your server depends remain running during the upgrade"
This advice is reinforced by the details of the article "OS X Server: Steps to take before upgrading or migrating the Open Directory database" (http://support.apple.com/kb/HT5300).
As the server I'm migrating from provides these services it will need to be running during the migration process. This would seem to limit my options to doing the migration from a Time Machine backup (or, making a seperate clone of the server's drive and connecting it externally to the new box)
My main concern is the seemingly inevitable clash that is going to occur on the network as the new server takes on the roles of the old one - while it is still running.
What are my options here ?
This is my second attempt as on my first try I did the migration from the TM backup with the network down - and none of my local network users or their home directories were migrated, although the settings for the mount points were, but there were no actual directories where they pointed to!
Clear directions on how to procede would be VERY MUCH appreciated
Thank you.

Answer 1

Moving from Snow Leopard to Mountain Lion means first installing the client (non-Server) version of Mountain Lion and then install Server.app this means that for at least part of the process you will not be running DNS, DHCP or Open Directory.
If you are going to end up using the same DNS name and IP address after the change then an approach you could follow would be as follows.
Destroy any Open Directory replicas
Archive your Open Directory Master (to make a backup)
Note down your DNS records in case they get messed up
Export via Workgroup Manager your users, and groups (you might not need this but better safe than sorry), make sure you do not include the diradmin account
Keep a full back of the server (you should always have backups)
Note down your DHCP server settings in case they get messed up
Note down any other service settings
Install Mountain Lion
Install Server.app
Install Workgroup Manager (extra free download)
Run Server.app
Make sure settings for services are as much as possible the same as before
If your lucky that may be all you need to do, otherwise...
Restore Open Directory archive, if your lucky that will be all you need to do, otherwise...
Make new Open Directory Master
Run Workgroup Manager
Import users and groups you previously exported
You will then have to set passwords for each user as these are not preserved via Workgroup Manager export
When I did this, I was also being forced to change all my IP addresses so I had no choice but to use Workgroup Manager to export and import accounts.