Desktop as a Service licensing policies can be almost as convoluted as the underlying technologies used to host...
Desktop as a Service (DaaS) is a desktop delivery model that allows organizations to offload virtual desktop hosting to a cloud service provider. Since it is not deploying in-house virtual desktop infrastructure, IT is released from the burden of managing on-site virtual desktops and avoids some infrastructure costs.
However, DaaS licensing is complex. Further complicating the licensing matter is the fact that every vendor and service provider has its own unique requirements.
DaaS in the public cloud
There are a few providers that offer DaaS in the public cloud. This form of DaaS is by far the simplest when it comes to software licensing. The DaaS provider purchases all the necessary licenses, and subscribers simply pay a monthly or annual fee to the provider to lease access to the remote virtual desktop.
One of the problems with this DaaS licensing model is that it can become complex when desktop applications are brought into the picture. Some providers include a standard set of applications (such as Microsoft Office) and build pricing for that set into the subscription fee. Other providers offer applications on an a-la-carte basis.
DaaS in the private cloud
DaaS licensing in the private cloud can become very complicated, depending on the software products you're using. Microsoft, for example, requires a Virtual Desktop Access (VDA) license for every device that accesses virtual desktops. The VDA license acts as the operating system license for the virtual desktop itself. For example, if you have clients accessing Windows 8 virtual desktops, then you need a series of VDA licenses, but you won't need any Windows 8 licenses.
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The retail price of the VDA license is $100 per device per year. VDA is required regardless of the underlying virtualization platform. The fact that users are accessing a Windows Client OS means that a VDA license is required. Microsoft uses the subscription-based model for VDA licenses, because virtual desktops are typically offered as a service. As such, there is no option to outright purchase VDA licenses.
The requirement for every device that accesses a Windows virtual desktop to have a VDA license probably seems simple enough, but there are other considerations. First off, VDA licensing is device based, not user based. Therefore, if you have a single user who accesses a virtual desktop from five devices, then that user requires five VDA licenses.
It is also worth noting that Software Assurance (SA) customers do not require a VDA license, so long as the device that is being used to access the virtual desktop is covered under the SA license. Other devices, such as home computers and non-Windows devices, however, still require a VDA license if they access a virtual desktop.
For those who do not like the subscription-based pricing model of the VDA, it is possible to purchase a full package product license (a retail license for a desktop OS) and run it on the virtual desktops, as long as the users are running the same version of Windows on the devices from which they are accessing the virtual desktops. However, it is usually much less expensive to lease VDA licenses.
Got VDA? You're not done yet
Operating system licenses. The DaaS user accesses the virtual desktop from a device, and that device presumably has an OS. If the device is running a desktop version of Windows (as opposed to an embedded version such as Windows RT), then a license is required for the desktop OS.
Desktop virtualization licenses. Licenses are also required for the desktop virtualization infrastructure. Windows virtual desktops can be hosted on Microsoft servers, or you can use infrastructure software from third-party vendors such as VMware or Citrix instead. In any case, the infrastructure software has to be licensed.
Each desktop virtualization vendor has its own licensing requirements. For example, Microsoft offers a license subscription called a VDI Suite, which is designed to complement the VDA license and provides access to all the basic infrastructure and management components required for desktop virtualization. VDI Suite licenses are leased on a per-device basis. Therefore, a user who accesses a virtual desktop from five devices would require five VDA licenses and five VDI Suite licenses (assuming that IT is using a Microsoft virtualization platform and the infrastructure is not covered by an SA license).
As you can see, DaaS licensing can be tricky. As such, some organizations will no doubt find that they are financially better off leasing virtual desktops from a public DaaS provider who charges a flat rate.