One very important aspect for multi-tenant environments is the licensing of the software components. While Citrix licensing allows cloud providers hosting multi-tenant, off-premise environments within the framework of the Citrix Service Provider program (further information can be found here: http://www.citrix.com/csp), for application software this depends on the licensing term of the individual software vendor.

Another major component of the DaaS – stack is the Windows operating system, which is the base for every virtual desktop. The Microsoft Services Provider License Agreement (SPLA) is the only Microsoft licensing program that allows service providers to license specific Microsoft software for cloud services hosting scenarios (further information about SPLA can be found here: http://www.microsoft.com/licensing/licensing-options/spla-program.aspx).

While the SPLA program contains scenarios that are designed explicitly for the physical desktop rental market and desktop-based applications, such as Microsoft Office programs or other worker productivity tools, it specifically forbids the use of its rental license for Desktop Operating Systems such as Windows XP, Windows Vista or Windows 7 in virtual environments, as stated within this document: http://download.microsoft.com/download/F/5/8/F58E786D-529D-438A-8625-4948205D8BA5/Windows_Hyper_V_Licensing_Whitepaper_v2_0.docx

This licensing restriction basically disallows Cloud Service Providers to prorate the cost of the Windows VDA license in the service offering. Instead, the DaaS end customers must pay for the full cost of the VDA license even if they only need to subscribe to a desktop for a few weeks.

Within a Hosted VDI scenario, it will therefore require the end customer to individually purchase licenses and provide them to the Cloud Provider for hosting the virtual desktops. A further restriction is that such licenses (purchased under a tenant’s volume licensing agreement) can not be used on hardware that is shared with other tenants. Thus, a dedicated hosting infrastructure per tenant is required, to avoid violating Microsoft licensing terms.

Source: Top 10 Considerations - Delivering Desktops in the Cloud, A DaaS Guide for System Integrators - Citrix White Paper, March 31, 2011