Lion Server Upgraders,
beware and proceed with caution.
Apple web site is naively optimistic on the upgrade process:
"To upgrade your Mac to OS X Lion, you don’t need to drive to a store, bring home a box, and install a bunch of discs. All you do is click the Mac App Store icon, buy Lion for $29.99, and your Mac does the rest. Just make sure you have what you need to download Lion to your Mac."
And then has a 3 step process...
This is completely miss leading.
Read this document first: http://manuals.info.apple.com/en_US/lion_server_upgrading_migrating.pdf
It will make it readily apparent that moving from Snow Leopard Server to Lion is not going to be simple.
Having done this twice now.. I have found that:
1. Open Directory migration is a weak point. Lion & Snow Leopard Open Directory are not compatible, so if you have masters & replica then expect trouble. I have an unresolved issue trying to get a simple Lion Server to Lion Server Open Directory replica up and running. This compatibility seems to also cause migration to fail, as I found that all my local User/Groups transferred ok but non of the /127.0.0.1/LDAPv3 (Open Directory) ones did. This is a very important item, as all the mail accounts in dovecot use LDAP generated UID, so you have to be careful that you do not loose mail accounts.
2. Mail - your mail aliases will not transferred, so you will need to reapply the aliases.
3. Web Server Setup - This broke, under migration as I gather the entire Web serving tree has changed. In particular I had "Snow Leopard" Web Mail (which is based on Squirel) on my "Snow Leopard" Server and this is now dead...
4. Digital Certificates - I found that the valid (ie signed by trusted CA's) did not get migrated, so I had to re-imported my Digital Certificates. If you have paid for third party CA certificates then make sure you have got these copied somewhere, as if you loose them then you will likely need to go to your provider and get a certificate revocation and new certificate, which will cost you money!
Cheers,
Zebity.