As you build out your desktop transformation project, you need to consider how big do you want to scale your XenDesktop sites, and at what point does risk enter into the equation.  If you’ve read Daniel Feller’s blog post on scaling XenDesktop sites, you’ll know what I mean.  XenDesktop can scale to very large single site infrastructures, but at some point, you will hit that tipping point from a risk perspective, and will need to look at building out your architecture in smaller, easily digestible modules to avoid the risk of a site failure affecting the entire user base. 

Enter the XenDesktop modular reference architecture.  The modular architecture breaks the various components required to deliver virtual desktops into three basic layers; access layer, desktop layer, and control layer.  Each layer is then broken up into modules and components that can be scaled as required to accommodate growth in the environment, and allows for multiple hosted VDI or hosted shared desktop site pods to minimize that risk of a single XenDesktop site failure.  

As its name suggests, the access layer contains the components that provide user access to the environment; NetScaler appliances and Web Interface servers.   The NetScaler does double duty as it provides secure access through integrated Access Gateway and also provides intelligent load balancing for the Web Interface, XenDesktop controller and XenApp controller infrastructure. 

The desktop layer provides the hypervisor resources required to host and deliver virtual desktops using the hosted VDI and hosted Shared FlexCast models.  Each pod in the desktop layer corresponds to a XenDesktop site or XenApp farm.  As the configuration grows in size, additional site pods can be added to the configuration to increase the number of virtual desktops delivered while allowing for lower risk and an element of redundancy. 

The control layer is home for the various controllers and infrastructure required for managing and delivering virtual desktops.  It’s divided into two general areas; per-desktop pod control elements and cross-datacenter control elements.  The per-desktop pod elements are unique to a desktop pod and provide the specific control elements required to keep it running; XenDesktop and XenApp controllers, and Provisioning Servers as required.  The cross-datacenter control elements serve the entire XenDesktop architecture. 

Want to know more?  Download the XenDesktop Modular Reference Architecture from the Citrix Knowledge Center or find it in the XenDesktop Design Handbook.  .  The document breaks down the specific layers and components and provides sizing guidance, as well as an example configuration.  And don’t forget to come see us at Citrix Synergy.  You will have the opportunity to get more in depth in the five-part desktop transformation series:

                Part1:  Getting started with your desktop transformation
                Part 2:  Successfully design your desktop transformation
                Part 3:  User experience design guidance for your desktop transformation
                Part 4:  Going live with your desktop transformation
                Part 5:  Keep your desktop transformation running smoothly

Rich Meesters – Architect
Worldwide Consulting Solutions 
Twitter:  @richski