Symptoms
Client requested information on how a Windows Server upgrade would affect his K2 software.
Diagnoses
Provided client with Microsoft article and compatibility matrix to show our compatibility with his server version.
Resolution
Upgrading a server to Windows 2012 R2 should not be an issue with K2 or SharePoint. Per this Microsoft article, https://support.microsoft.com/en-us/kb/2891274, SharePoint Server 2013 SP1 is supported in Windows Server 2012 R2. Our compatibility matrix, http://help.k2.com/blackpearl/support-matrix_Windows, indicates that 4.6.9 is supported in Windows 2012 R2. There shouldn't be any issues when upgrading a server OS to Windows 2012 R2. The only issue that I can foresee coming up is if the server name is changed to something other than what K2 already has. There is no documentation listing possible issues with upgrading the OS on a server with K2 on it. My best advice for any issues you may encounter is to open a support ticket and we will be more than happy to assist in helping fix the issue.