Where does application layering fit in the virtualization puzzle?

App layering is a valuable tool for IT pros looking to virtualize applications because it allows them to deliver specific apps to specific users based on a wide range of criteria.

Layers are everywhere. At a wedding, there's bound to be layer cake. Anyone who goes out in the frigid cold of winter puts on layers to stay warm. Earth itself is made up of layers. So it's only natural for layers to be a part of application virtualization.

Application layering may still be somewhat of a niche technology, but its versatility is helping it gain traction because it allows some IT administrators to pinpoint the exact users who need to work with specific apps and to deliver the apps directly to them.

As this burgeoning technology continues to grow, IT admins must understand how it works, how it compares to application virtualization and who the big players are in the market.

What is application layering?

Application layering is a method for delivering virtual apps to end users based on different criteria, such as group or location. It helps admins deliver the right apps to the right users. The apps run on a layer separate from the virtual desktop itself. Admins can make changes to the apps, update them and manage them separately from a virtual desktop's base image. As a result, admins have fewer base images to deal with, and may even be able to use a single golden image for their virtual desktops.

Apps delivered through layering interact with the operating system and any other apps as if they were installed locally. Application layering is ideal when virtual apps must communicate directly with users' devices, kernel drivers or other apps.

How does application layering work?

Each application layering tool is unique, but they all follow a basic three-layer structure. The bottom layer is the virtual desktop's primary hard disk, where the virtual desktop operating system lives. The middle layer is home to everything that puts meat on the apps' bones, including binaries, registry keys, drivers and more. The final layer hosts users' profile data and keeps it separate from the operating system.

One way to think of it is like a sandwich. The bottom layer and the user data layer are the bread, which every sandwich needs. The middle layer includes the ingredients, which change depending on the sandwich.

Each application layering tool is unique, but they all follow a basic three-layer structure.

Individual applications usually make up their own layer, which is what allows admins to deliver specific apps to specific users. As a result, IT admins may deliver more than three layers to a particular user. They deliver the bottom and middle layers, as well as the user profile layers for each application the user works with.

How does application layering differ from application virtualization?

VDI shops should not consider app layering as a replacement for more conventional app virtualization tools, such as Citrix XenApp or VMware ThinApp. Virtualization tools can deliver apps that are not compatible with the base operating system, but app layering is dependent on the OS.

Another difference is that application virtualization tools such as XenApp and ThinApp run into process isolation issues, where each application runs completely separate from the operating system and any other applications. As a result, the applications cannot communicate with each other as well.

What are the top app layering tools on the market?

There are three major products in the application layering game: VMware App Volumes, Liquidware Labs FlexApp and an offering from Citrix. Citrix is replacing its AppDisk product with technology from Unidesk, which it acquired early this year. 

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