Virtual desktops mean virtual applications
You can’t have one without the other
Desktop Virtualisation Virtualising the client is not just about the desktop. It is also about application virtualisation.
“Half of large organisations with more than 5,000 PCs have already adopted application virtualisation,” says Gartner analyst Terry Cosgrove.
That compares with perhaps one per cent worldwide that have adopted a virtual hosted desktop infrastructure (VDI).
In fact, it is hard to virtualise the desktop unless you also virtualise applications. “We see this as almost a prerequisite. If you think about how VDI would work at scale, you need some way of layering the applications onto a virtual desktop. Otherwise you will have each user with a dedicated image and you won’t get cost savings,” says Cosgrove.
Image is all
What is application virtualisation? Like desktop virtualisation, it comes in several guises. One long-standing variant is where the application runs on the server but the user interacts with an image of the application window. Microsoft’s RemoteApp  works like this, and so does Citrix XenApp  in its session virtualisation mode.
This type of solution has its place but there are performance and availability drawbacks. Another type of application virtualisation overcomes these by running locally, but in an isolated environment that does not touch the system state of the host computer.
Dependencies such as DLLs and other components are packaged into a bundle. Examples are Microsoft’s App-V , Citrix XenApp in application virtualisation mode, VMWare ThinApp , and Symantec’s Altiris Software Virtualisation Solutio n. The resulting bundle can either be installed on the host PC or streamed on demand.
Preparing an application package can be a chore. The process for App-V, for example, involves installing the application on a test base machine while the App-V sequencer monitors the install.
Once done, the sequencer creates a package that captures the changes and dependencies and packages them for execution by the App-V client. Sometimes some clean-up work is necessary. Sequencing needs to be done every time the application is updated.
Once the package is created, though, the user experience is good and administrators get a near-guarantee that it will run successfully, without dependencies and setup failures.
Not all applications take kindly to virtualisation
“Our data shows that overall packaging and testing time can be reduced by 60 per cent,” says Cosgrove. “A sample of 24 organisations we surveyed in the fourth quarter of 2010 reported an average reduction of help desk calls by 18 per cent.” (The figures relate to application virtualisation generally)
The most obvious reason to virtualise applications. is compatibility, a common example being Microsoft’s Internet Explorer 6.0.
“Microsoft actually prohibits that but it’s a very common use case,” says Cosgrove. The reason is that IE 6.0 does not run on Windows Vista or 7, but is required by some legacy web applications.
Another reason to virtualise is simply to avoid setup and dependency problems. Some organisations are using application virtualisation as a run-up to a VDI.
Unfortunately, not all applications take kindly to virtualisation. According to Gartner’s research, about 20 per cent of applications cannot be virtualised and about half should not be virtualised.
They include applications that rely on device drivers, or that start running before user log-in. Applications like Microsoft Office which have many integration points with the operating system are poor candidates, and it is probably better to make this part of a base operating system image rather than attempt to virtualise it.
Application streaming, where the application is downloaded on demand, is a compelling approach which is not yet widely adopted. Streaming gives IT admins a little more control over deployment.
You can set up applications to block streaming once the licensed number of concurrent users is exceeded, for example. Or you can ensure that users run only the latest patched version. Offline use is possible using a local cache, blurring the boundary between streamed and non-streamed approaches.
In the end you cannot contemplate virtualising the desktop without first figuring out how to run the applications users require.
“Provision the users with the applications they need, regardless of how, with what device, and where they are consuming it,” says Fredrik Sjostedt, EMEA president at VMWare.
This type of application-centric approach makes sense. If desktop virtualisation is the destination, application virtualisation is likely to be part of the journey. ®