Most big vendors have a licensing structure that is often times a bit more complicated and cumbersome than we would like it to be. Furthermore, it can lead to unnecessary costs if not carefully analyzed upfront. Microsoft is no exception and the combination with Citrix can sometimes cause confusion as to what type of licenses are needed to build a new XenApp environment or expand existing systems. For Citrix to work on Windows, you will need to license two components—the operating system and Remote Desktop Services (RDS). Here is a list of licensing options from Microsoft that support virtualization at the time of writing this book:
Operating system: The following types of servers are supported:
Virtual servers: The following virtual servers are supported:
Windows Server Standard Edition: One license is required for every two virtual machines (guest OSes).
Windows Server Datacenter Edition: One license is required per hypervisor host, granting unlimited VMs (guest OSes) running Windows within a particular host.
Physical servers: The following physical servers are supported:
Windows Server Standard Edition: One license is required for every single-processor server, and two licenses are required for every four-processor server.
Windows Server Datacenter Edition: One license is required for every single-processor server, and two licenses are required for every four-processor server (same as Standard).
Remote Desktop Services: A license is given per user or device (also known as CAL), and in the context of Citrix, one license is required for each user to connect to a XenApp server; the license will be tied to this user.
With regard to an OS, today, many companies use a Key Management Service (KMS) server to manage the volume licensing of their enterprises. KMS is supported by Citrix as a central licensing authority for Windows and Office and is by far the most popular method for license activation. It is always beneficial to have a conversation with your Microsoft sales representative or a Microsoft reseller to ensure that you get the best licensing mix for your budget.