Friday, June 8, 2018

Breakdown of Citrix XenServer and XenApp

I've recently spent a some time working with VDI products and thought it would be helpful for me - and hopefully you - to document the interconnections between these various products. 

For this example we will use Citrix XenServer and Citrix XenApp as the carrier for VDI. In order to bring VDI to the end user, at the office or at home, other components are required. In order for an external user to connect to VDI, they are first met by a Citrix NetScaler Application Delivery Controller. The NetScaler is a networking appliance that determines the appropriate path for the best user experience. This appliance determines which StoreFront is currently the best server to provide a desktop. Data compression and load balancing are key features of the NetScaler. The user is then passed to a CloudBridge, which behaves similarly as the NetScaler. Multi-session compression, protocol acceleration, traffic shaping and TCP protocol acceleration. Internal users will not be confronted by a NetScaler, internal users will be provided compression and load balancing via the CloudBridge. Now that the networking aspect is complete, the user finally reaches the Data center. 

Within the Data center the VDI request initializes a StoreFront Server session. The StoreFront server simply provides a selection of desktops available to the user. All users will see the Standard Desktop. Some users will be able to select the Administrator Desktop. Select users may have Test Desktop available. Once a desktop selection is made the session request is pushed to a Provisioning server. This component houses the images used for each desktop. The Provisioning Server determines which desktop is available on which Delivery Controller and passes the request. The Delivery Controller ingest the desktop selection request and assigns a virtual desktop agent (virtual computer). The desktop is returned to the user and productivity for the day can begin. The NetScaler is hosted on a Linux operating system. Linux is also installed on the CloudBridge. The remaining components have software installed on a Windows Server 2008R2 virtualized platform. The Citrix XenApp server provides users with individualized access to software. Software with stringent licensing restrictions are hosted via the XenApp server. The company can then determine which users have a valid need for the limited licenses for applications like Adobe Creative Cloud products, Microsoft Visio or Project. The XenApp server also allows for access to be restricted to specialized personnel. For example, the Closed Circuit TV monitoring software can only be accessed by Security personnel.

On the user side, this change is really very minimul. However, it is a change, and change is seldom welcome. It has been noted there is an additional step during the login process. Users must authenticate with the StoreFront and again to login to the system. This additional step seems to be a bit more than people are willing to tolerate. Network performance is the other point of contention among users. Many users feel as though the old laptop they had to do their work was much faster than VDI. Performance wise, there is nothing to support this claim. Each VDA is configured to used 12GB of RAM and 160GB of space. A performance monitor indicates a similar transaction (updating a spreadsheet) occurs quicker within VDI. However, reading an encrypted email takes much longer in VDI.

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