Windows Server 2012 R2 introduced a feature called “Automatic Virtual Machine Activation” (AVMA), and now in Windows Server 2016, this feature has been carried forward. This feature was primarily designed for Web Hosters but found usefulness in internal Hyper-V server for testing lab machines.

What is Automatic Virtual Machine Activation (AVMA)?

Automatic Virtual Machine Activation is a feature that handles the activation process for an instance of Windows Server inside a Hyper-V virtual machine so it does not need to directly contact any other system to activate the Windows Server instance.

AVMA is engineered to digitally facilitate the guest virtualization rights allowance of the Windows Server Datacenter license. If the physical host is properly licensed to run Windows Server Datacenter, then any number of virtual instances running the same or a lower edition and the same or earlier version of Windows Server is included.

Requirements for Automatic Virtual Machine Activation?

You must have a Datacenter Edition of Windows Server 2012 R2 or Windows 2016 installed as the management operating system with the Hyper-V role enabled. AVMA is a feature of the operating system, not Hyper-V itself.

How to Configure a Virtual Machine for AVMA?

When prompted for a license key, you simply give it the key that matches the operating system of the virtual machine.

Guest Operating System’s and Keys

Windows Server 2012 R2 Essentials
K2XGM-NMBT3-2R6Q8-WF2FK-P36R2

Windows Server 2012 R2 Standard
DBGBW-NPF86-BJVTX-K3WKJ-MTB6V

Windows Server 2012 R2 Datacenter
Y4TGP-NPTV9-HTC2H-7MGQ3-DV4TW

Windows Server 2016 Essentials
B4YNW-62DX9-W8V6M-82649-MHBKQ

Windows Server 2016 Standard
C3RCX-M6NRP-6CXC9-TW2F2-4RHYD

Windows Server 2016 Datacenter
TMJ3Y-NTRTM-FJYXT-T22BY-CWG3J

These keys will be accepted by any operating system but if AVMA is not detected they will move into an unlicensed mode.

Ref: https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-R2-and-2012/dn303421(v=ws.11)