I have a number of very memory/cpu intense .net applications that would like to look at moving to 2008 R2 server core, core seems like the perfect solution from initial review, we have a lot of Server 2003 VM's that were P to V's and I think we are wasting a lot of host resources on these. All apps run on either .net 3.5 or 4, is there a problem with using server core like this.
2008 R2 Server Core only supports a subset of .NET. Here's the documentation on Server 2008 R2 and .NET:
On a Server Core installation and on a full installation of Windows Server, you can enable the .NET Framework by installing the optional features for it. You cannot enable the .NET Framework by using the downloadable .NET Framework redistribution packages.
So upon first inspection, no .NET 4 for you. But I think that documentation is a tad outdated, and you can still find an installer for .NET 4 specifically for Server Core...
Yep, here it is: http://www.microsoft.com/en-us/download/details.aspx?id=22833
But you're likely still going to be limited in what .NET namespaces are supported in 2008 R2 Core:
Server Core contains the normal complement of .NET namespaces with a few exceptions. This list contains, by name, the namespaces that are missing from a Server Core installation.
• System.Speech • System.Web.UI.Design
Design time support is unavailable. Runtime support for expression builders is supported.