Windows DataCenter and the VM license key dilemma

I had to write about this, because it's driven me batty. I wanted to get this written down to have a record I could refer to, and also to possibly help some other frazzled IT guys out there. So here was my scenario:

• Windows 2012 DataCenter was purchased, installed, and configured with hyper-v.
• Believing that I could install an unlimited amount of VM's in this version, I happily began creating my VM's and templates, not worrying about the pesky license key when I started.
• The VM's I installed were Windows 2008 R2 Standard.
• When it came time to license them, I logged into the Microsoft volume licensing site and lo and behold...I could not find a license key for Windows 2008 Standard. What to do?
• I tried using the 2012 DataCenter key on my 2008 R2 VM's. No good!
• I tried using the 2008 R2 DataCenter key on my 2008 R2 Standard VM's. No good either. But interesting that there is a key for 2008 DataCenter and not Standard. Hmmmm...
• Start an intense web search, trying to figure out where I get the keys for my unlimited number of 2008 R2 Standard VM's.

Eventually, I came upon the answer to my question. If you buy 2012 DataCenter and want to run VM's on it, the VM's must be DataCenter (2008 or 2012) also! So my 2008 R2 Standard VM's needed to be upgraded to 2008 R2 DataCenter. OK great, but how do I do that? It turns out it's not that difficult, but there is an order of operations to follow. You first need to upgrade to Windows 2008 R2 Enterprise, reboot, and then upgrade to Windows 2008 R2 DataCenter, reboot again, and then use your 2008 R2 DataCenter license key to activate the product. But what keys do you use to perform the upgrades you ask? It turns out there are public KMS keys which you can use to do this, even if you don't have a KMS server and will eventually be using an MAK key. In my particular case I had to run an elevated command prompt and use the command:

Dism /online /Set-Edition:ServerEnterprise /ProductKey:489J6-VHDMP-X63PK-3K798-CPX3Y

then reboot...and then....

Dism /online /Set-Edition:ServerDataCenter /ProductKey:74YFP-3QFB3-KQT8W-PMXWJ-7M648

reboot once more...and then go ahead and enter your actual key. You are done! If you are going through the same upgrade process that I went through, you can copy and paste the commands above. Those are the public KMS keys for Windows 2008R2 Enterprise and DataCenter. You can't use those keys permanently unless you have a KMS server. Hope this helps somebody!