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Explore how application layering works and why to consider it

Application layering offers an alternative to app virtualization or installing apps directly on the virtual desktop. This approach can save IT valuable resources.

IT is constantly on the lookout for ways to simplify difficult management tasks, and application layering is another tool they may want to add to their lists.

Application layering is a technology that delivers applications to a virtual desktop without those applications actually having to be installed on the virtual desktop OS. By separating the application from the OS, IT is able to manage fewer OS images than is required if applications are installed directly on the virtual desktop.

App layering is not app virtualization

The first thing to understand about application layering is that it is different from application virtualization. Application virtualization packages apps in a way that allows them to run independently of the OS. In fact, sometimes IT uses application virtualization as a mechanism for running otherwise incompatible applications. Conversely, application layering relies on the desktop OS, and does not shield the application from the OS the way that app virtualization does.

App layering does not shield the application from the OS the way that app virtualization does.

Another key difference between application virtualization and layering is that app virtualization often results in process isolation. Depending on the tool IT uses, each virtualized application may run in its own isolated space, making it difficult for applications to interact with one another. Layered applications, on the other hand, behave just as they would if they were installed locally. The way in which application layering works varies depending on which vendor's tool you use as well.

Consider what normally happens when an application gets installed to a Windows PC: The application's setup program copies the application binaries to the PC's hard disk, but it also makes some OS-level changes to make it aware of the application. Typically, this means adding keys to the Windows registry to register the application's file extensions, adding the application to the Add or Remove Programs list, and enabling key configuration items. An application layering tool captures all the changes made to a PC as a result of installing an application and isolates those changes into a so-called layer.

Discover what's in each layer

Each app layering vendor has its own way of doing things, but generally a virtual desktop that is running a layered application has three separate layers. Each of these layers commonly exists as a virtual hard disk file.

The bottom slice of bread
The bottom layer of the stack is the virtual desktop's primary virtual hard disk. This virtual hard disk contains the operating system.

The meat
The middle layer contains the application itself. Like the base layer, the application layer exists as a virtual hard disk. This layer contains only application binaries, application-specific registry keys and anything else that the application writes to the operating system, such as drivers and dynamic-link library files.

In some cases, this layer is created through the use of a utility that intercepts write operations during the application installation process. Such an application would be initiated just prior to installing a copy of the application onto a clean operating system. All intercepted write operations would then be written to a dedicated virtual hard disk that will become a layer.

Other application layering tools create the application layer through snapshotting. In this situation, it creates a differencing disk snapshot just prior to deploying an application. The resulting virtual hard disk contains everything that the application needs to run.

What do you know about application layering?

App layering is a helpful virtualization tool. Show off your knowledge of the topic with this quiz on what criteria IT can use to layer apps, where app layering hard disks live and more.

The top slice of bread
The third layer in the stack is the user data layer. This one contains the user profile that the Windows operating system uses. It is designed to isolate the user profile from the virtual desktop OS to preserve the operating system's integrity.

The condiments
The layering process is commonly described as three layers that come together at run time, but real-world implementations usually include far more than that. This is because each application usually gets its own layer. This approach provides a degree of separation between applications, allowing IT to deliver the exact combination of applications that a particular user needs. If a user needs five different applications, then IT uses seven different layers, including an OS layer, a user profile layer and a layer for each of the five applications.

Application layering is a good alternative to application virtualization or to installing applications within VDI images. Layered applications behave just as they would if they were installed locally but leave the OS detached from the application, thereby reducing the number of images that an organization must maintain.

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