Is upgrading as simple as installing Lion Server from the App store? I've heard that you have to be running Lion first to be able to install the Lion Server software, but I'm looking at upgrading a live server and need to know how others have gone about it and the problems they ran into. Thanks :0)
Well, I would advice clearly against doing this for a live system at the moment. Don't fix it if it isn't broken.
Lion Server has a completely revamped UI, it takes quite a bit of time to reconnect all the bits and pieces. It does a lot under the hood which used to be exposed in Server Admin. DNS / DHCP / other low level services are still available, but not exposed in the default UI anymore.
Set aside a separate machine, learn to find your way in the new UI, and then you may choose to upgrade your live system or not.
I upgraded to OSX Lion server 10.7.2 from Snow Leopard server with no problems. I purchased to server upgrade: it tried to install immediately, warned me that I did not have Lion, told me I had already purchased Lion (which I had installed on a macbook previously). Then nothing appeared to happen. While I was looking for advice on sites like this, after about 20 minutes the 'Do you want to install Mac OS X" screen popped up. Lion must have been downloading in the background! On selecting 'Continue', it started 'downloading additional components' with a forecast of 3 hours 52 minutes. This reduced a minute at a time for 3 minutes, then forecast 32 minutes. After 29 minutes total (from the start) it rebooted to server, configured services, upgraded OD to 10.7.2, upgraded users, upgraded services That took 6 minutes. (35 minutes from the start) it rebooted again, prompted to configure iCloud.
No settings were lost. VPNs, share points and shared screens were preserved. (But I had to restart screen sharing on a client that was active during the reboots, not a big deal)
I've been holding off upgrading after reading the apple documentation and finding that some features available in Snow Leopard Server won't be available in Lion Server.
Don't upgrade just yet. Wait at least for 10.7.1. That said, the upgrade is pretty straight forward. If you go to the Mac App Store on the Server and try to buy Lion, it'll tell you, you need to buy the server components too. Do that and then it'll download the two packages and upgrade to Lion Server in one go.
After the upgrade you'll be surprised to find only a very simplified Server Admin app. You need to download the 10.7 server admin tools (the one you're used to) from Apple as they don't come preinstalled anymore (i wonder why). You get them here.