On 2021-01-21 Kevin McGregor wrote:

Oops! Brain tired. Should read "If the two Linux hosts have the same
CPUs (manufacturer and gen) you should have no problem".

Yes, in this case the physical hardware would be identical.

Means nothing. There's still the GUID of the mainboard, which is very much different even when everything else is the same.

However, there is conflict between Alberto's & Kevin's answers... has
anyone actually tried it?

I do have experience with Windows and its activation perks... mostly for the consumer version, which incidentally is what you want.

And for sure you weren't using a corporate Windows license key?  (And
not a Server version either.)  I recall hearing something like Alberto
said re: non-corporate Windows detecting it was in a VM and complaining.

I am less concerned about the "being on a VM" and more about "making sure you have a reliable anchor for it". It would not matter for a sitting duck, but you want to dance around with it. I am reasonably sure that you don't want to be typing lengthy codes on your phone when calling the Microsoft Activation Hotline. (Thank you for calling Microsoft! Which product would you like to activate? Please say Windows, Office, ... ugh).

Even then, we want to abide to Microsoft's terms.

And here (https://www.microsoft.com/en-us/Useterms/Retail/Windows/10/UseTerms_Retail_Windows_10_English.htm) we find:

b.      Device. In this agreement, “device” means a hardware system (whether physical or virtual) with an internal storage device capable of running the software. A hardware partition or blade is considered to be a device.

(iv)    Use in a virtualized environment. This license allows you to install only one instance of the software for use on one device, whether that device is physical or virtual. If you want to use the software on more than one virtual device, you must obtain a separate license for each instance.

Keep in mind I am not a lawyer (really? lol). Now, as with everything Microsoft licensing, this is ambiguous enough to have you thread the grey area if you have a single licence for the dancing VM, as it states a device meaning a hardware system, physical or virtual. It does mention "one virtual device", and we can argue that we are talking about a single virtual environment , even though it sometimes travels between different hosts. Now, we are talking about consumer, retail versions here, so I may not be grasping at straws when I point this. That said, keep in mind that I am not a lawyer (you don't say? :D), so my opinion is worth...yeah. That said, stay with me.

Even assuming that would be perfectly legit, you still have the problem of keeping the activation when changing hardware. The virtual environment may be abstract enough that it does not detect enough of a change and just pretends nothing ever happened. Or it does smell a rat and asks for activation. Well, please see above if that happens. In this case, if our assumption is right, it would be OK for licensing, but not nice at all to administrate.

I guess the big part of the question is, if Windows doesn't have a
blanket anti-VM block in it, how much of the host hw id info really
does "seep" into to guest...

As much as you let in, for KVM at least.

The problem here that testing it might "waste" a paid Windows license.
Even if we bought 2 licenses and activated twice, I'm not convinced the
activation code won't get angry at going back and forth between the 2
boxes.

It will not, because the code goes to Microsoft only once. When you pass the tables like I described on my previous email, it results in a hash that Windows is able to pass onto the activation servers.

- Hardware hash is passed to Microsoft activation servers.
- If there is no key tied to it, it reports "not activated". Boo. Gimme key!
- You have the key in. Let's say, Pro version.
- Key is now tied to the hash.
- You're activated!

So now you nuke it from orbit and start fresh. Same process happen again, but this time:

- Hardware hash is passed to Microsoft activation servers.
- Uncle Bill says: "oh, I remember you! You have a licence here, but let's talk first: what are you, really?"
- "I am a Pro, dude, but I have no l33t codes on me, sry"
- "Just as I remembered. Sweet! I remember your l33t codes from times gone by, no need to bore me again. Here, a cookie. Off you go."
- Activated!

And that alone is *enough*. With that, it quickly finds out if you're activated or not, and off it goes. No key, no rearm, nothing. You will *never* be prompted for a key if there is a valid licence tied to your hardware's hash, thus, by passing the SLIC bits to the VM, and that physical hardware having a good valid Windows 10 licence previously activated with Microsoft, it will just take care of itself. Done. You will never type a key for that hardware ever again, assuming you 1) never phone-activate the key on another device, thus revoking the authorization for the one to which it is tied (true for RETAIL versions, keep that in mind, as OEM licences are not able to be revoked in this manner, at least theoretically); and 2) use the same version of Windows (e.g. Windows 10 Pro key = Windows 10 Pro install. Home = Home. You get the idea).

That also means that both machines would have a Windows licence *tied to their hardware*, which could be used even after the VM setup is no longer warranted, either for another VM, or for a bare metal install should it ever be repurposed as a beefy workstation, for example.

Now, it remains to be seen if that's feasible using VirtualBox. As I said, one is able to do that with KVM.

Man, do I hate Windows and non-FLOSS.  Maybe I need to see if my
customer could instead forget Windows and make everything work in
WINE...

As you mentioned WINE, I suggest you investigate that and see if he is happy. If that is not an option, let me know and we can research something that is sure to steer your client far away from uncle Bill's fury.

Kind regards,
Alberto Abrao