So, what is Citrix XenApp?

XenApp server 6.5 is the current remote desktop server solution from Citrix, a Florida-based company. It is reliant on Remote Desktop Service (RDS) and Microsoft Windows Server 2008 R2; however, XenApp expands upon the functionality purely offered by Microsoft.

By remote desktop server, we mean that users can connect remotely to the desktop or published applications on that server. More often than not, users connect to published applications and not the server desktop (Citrix XenDesktop providing the specialist connectivity to desktops). Once connected to the published application or server desktop, the applications run using the server's resources such as memory and CPU, and regardless of the connectivity that the user has, however remote, the application will run as if it were local to the user. One major advantage that Citrix provides against the competition is that the user's local device can be virtually any computing device from a Windows PC to Apple Computers (Mac), Linux desktops, smart phones, and also tablet PCs that include the Chromebook and Blackberry PlayBook as well as the more obvious iPads and Android devices.

Now that we know the device can connect remotely, we have to make sure that it has the Citrix client, or what is known as the Receiver installed (the Receiver can be downloaded from Citrix (http://www.citrix.com/downloads/citrix-receiver.html), or from central application repositories such as Apple's AppStore and Google Play). Once installed, the Receiver can make a connection to the XenApp server farm, and a list of available resources displayed back to the user. The connection will use the proprietary Citrix protocol, Independent Computing Architecture (ICA). This highlights more advantages that XenApp offers:

• Virtual channels that can be independently controlled for desktop features such as clipboard, printing, sound, and drive mapping

• Local Flash playback that can play Adobe Flash movies on a local device rather than a server

• Windows media redirection, as with Flash, can be compressed and can send movie and sound files to the client to play locally-freeing resources on the server (if the client has the correct local software)

• Integration with Microsoft Lync server for video conferencing

All in all, the architecture used for client-to-server communications can greatly reduce the bandwidth required on a recent project where the requirement is for local PCs to scan customer's correspondence, using remote application servers. We established baselines that each client required, on an average of 250 Kbps using Microsoft RDS compared to 100 Kbps when using Citrix XenApp 6.5.

Note

The scanner would be attached to the client's device; however, the scanning software will run within XenApp. The input from the scanner is transferred, in this case via the TWAIN virtual channel of the ICA connection, from the client to the server.

Besides the Citrix XenApp servers that will host the users' sessions, we will need other server resources such as:

• A database server to host the farm database

• A license server to issue concurrent user licenses

• A Web Interface server to present resources to the user that are available on the XenApp Server

Ideally, these all would be on separate servers, but a single server can potentially provide all server resources, including XenApp. This would not be recommended but is acceptable for a proof of concept system, where the need to demonstrate XenApp is required.

Management is maintained through the graphical tool Citrix AppCenter, for those needing a more scriptable style of management. PowerShell modules are provided to allow easy command-line capabilities. In the following screenshot Citrix AppCenter is shown:

XenApp gives you and your users the ability to run applications remotely, as if they were in the office, regardless of the devices they connect from. This enables greater productivity and flexibility in working arrangements. Within your main office, user desktops can be replaced with thin devices that require little or no maintenance, and can additionally reduce power consumption from an average of 400 watts to 5 watts per device.