Real-Time App Delivery for Citrix XenApp and VDI – a Deeper Look at Unidesk Elastic Layering

Posted by Thomas Willingham on Jul 27, 2016

Elastic LayeringTM was announced back in April, when we provided a preview of how Unidesk 4 could deliver unique apps in real time to Citrix XenApp sessions. This new ability to attach virtual disks at login and give XenApp users logging into the same server different apps was one of the reasons that Unidesk 4 won Best of Citrix Synergy Award for New Technology. Now that this capability is available for XenApp, and for VDI – it’s time to  take a deeper look at the technology. After my technical overview, I include a short video by our Chief Solution Architect Ron Oglesby that visually explains how Unidesk Elastic Layering works.

What is Elastic Layering

Elastic Layering extends the capabilities of existing desktop virtualization deployments and enhances user customization. Elastic Layering attaches virtual disks at login using in-guest virtual disk (VHD) mounts. These layers are self-contained and session-aware. This is ideal for departmental and one-off apps that are only used by smaller numbers of users. Unidesk looks up the apps that a user is entitled to based on AD user and group membership and attaches the virtual disks assigned to that user.

Let’s step back and think about this for a minute. One of the limitations of session-based computing; Citrix XenApp, or RD Session Host environments, is that a new silo or server needs to be created for each unique set of applications.

What if you could use your existing session-based servers to address the main user needs, and then use Elastic Layering to add personal or departmental applications for users as needed? This enables session-based computing to offer more of a customized user experience, similar to VDI.

Two users on the same XenApp or RD Session Host server can have different sets of apps, while maintaining fewer silos . . . mind blowing, right?

Elastic Layering isn’t just for session-based computing; it works in VDI environments also. You can use Elastic Layering to customize pooled, non-persistent desktops, giving them the look and feel of a persistent desktop with less cost and resources.

A Technical Overview of Elastic Layering

Unidesk has implemented a next-generation, patent-pending design that makes Elastic Layering extremely easy to deploy and highly fault-tolerant. No new infrastructure needs to be created, no databases need to be deployed, no additional replication needs to be added. The layering service looks at the layer repository, which is a simple file share, and reads two files:

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  • ElasticLayerAssigments.json – lists the applications that are associated to specific groups
  • Layers.json – lists VHDs that contain specific applications

The service then mounts the appropriate VHDs from the Layers\App folder. This system is completely portable, self-contained and replicatable, due to the fact that the directory contains all of the applications and the connectivity information needed. The directory can be hosted in any cloud or on-premises environment. Just point the data center to the file share’s UNC path and you’re set. This path to the share and files is configurable by editing the registry, allowing different systems to support different paths, which is useful for larger deployments and disaster recovery.

Scaling Elastic Layers is straightforward. All you need to do is copy the layer repository for redundancy and ensure fast access at user login. The layer repository is read-only - the desktops don’t make any changes to these applications which makes file synchronization between the two sites simple. You just replicate the file share.

The only thing that could make this post better is a video overview of Elastic Layering from our Chief Solution Architect Ron Oglesby.


Elastic Layering is a powerful application delivery approach that can be used to expand session-based computing and VDI deployments. Many enterprises are starting to deploy Elastic Layering to eliminate costly PC refresh cycles, and get more out of their existing Citrix XenApp investments by extending digital workspaces to all apps and all users. Imagine how much IT budget you could save by not buying hundreds or thousands of new $1,000 physical desktops, and instead reuse your old PCs as thin clients. Or, buy cheaper, more energy-efficient zero clients to connect to your new hosted workspaces. Unidesk Elastic Layering makes both possible. 

What additional features and functionality would you like to see in Elastic Layering? Write a comment to let us know!

Topics: VDI, Citrix XenApp, Elastic Layering

Posted by Thomas Willingham on Jul 27, 2016

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