Before discussing enabling the Hyper-V role, this section covers configuration levels,
which was a new concept in Windows Server 2012 that was built on Server Core,
introduced in Windows Server 2008. Server Core was a minimal installation of the
Windows Server operating system with no graphical shell, no management tools, no
.NET, and no PowerShell, and it was designed to run certain Windows Server roles
such as Active Directory Domain Controller, Hyper-V, and File Server. The goals
behind Server Core were to have an operating system with fewer components that
were not required for many server roles and therefore to cut down on patches needed,
reduce possible vulnerabilities, and reduce the number of reboots associated with
patches. There was also a small resource overhead reduction. This goal was a good
one, but Server Core was hard to manage and could not be used with Server Manager
remotely, and people largely ignored it. Windows Server 2008 R2 improved on this
with remote management via Server Manager and PowerShell support, but the hard
choice at installation time made using Server Core scary, and it’s still avoided by most
IT organizations.
Windows Server 2012 changed this inflexible choice at installation, enabling the
graphic shell and management tool features to be added and removed like any other
feature, which made it easy to switch a server from being in Server Core mode to being
a full server with a graphical interface. Additionally, more granularity was introduced
to allow different configuration levels, which are shown in Figure 5.1. Notice that with
configuration levels, it is possible to remove the graphical shell but still have the
management tools available locally to the server. The default installation option for
Windows Server 2012 and above is now Server Core, which shows the shift to Server
Core being “the norm” for a Windows server, with nearly every Windows role and
feature supported on Server Core in Windows Server 2012 R2. In addition, for
applications to receive Microsoft’s Gold Certification, which is the highest level of
application certification, the application must run without the graphical shell
installed. The Windows Server 2012 R2 Server Core base footprint is about 1GB
smaller than Windows Server 2012 Server Core, thanks to new optimizations and
compression of optional features that are not actually installed.