Thread: Virtual Desktop Infrastructure

In the early days ot computing, there were no PCs. Instead, there were terminals and they were 'dumb', in that they did not have a CPU or a hard disk. The processing unit was a gigantic computer called the mainframe.

Then Then the PC, in its many incarnations, came along. So did evils like computer viruses, high power consumption and technological obsolescence. Using PCs is a costly affair for corporates. Time for the next wave in computing:

Remote/Thin Clients and virtual desktop infrastructure (VDI). To explain this model we'll cite the unified solution of HP, VMware and Citrix. Similar solutions are available from other vendors like ClearCube and Cubix.

PC users are familiar with the term 'desktop' which refers to an environment created by the operating system. This environment includes all your programs, documents, email and settings for the as and applications. A virtual desktop is one that appears to be on the client, but really isn't-the desktop is actually on a PC or server in a data center. Images of that desktop are relayed to the client and refreshed whenever a user of the program makes changes. So what you see on the client is really an image of the qesktop-a 'virtual'desktop A virtual desktop manager is required to manage, maintain and update each virtual desktop image, along with all its installed applications and user settings.

Citrix XenDesktop is a virtualization technology that uses something called 'desktop delivery'. Based on a user's profile, XenDesktop assembles virtual desktops on demand. So you get a clean and new, yet personalized desktop every time you log in. Here's how XenDesktop manages virtual desktops.

1. AUTHENTICATION

A user logs in using a thin client or a Pc. He gets an authentication screen for his login details. On logging in an image of the virtualized corporate desktop appears.

2. DESKTOP ASSEMBLY

Once a user is authenticated, a module called the Desktop Delivery Controller (DOC) identifies the user profile and dynamically assembles his virtual desktop. The operating system is loaded from the hosting infrastructure. The as reads the user's profile and loads the appropriate applications from the application server.

3. DESKTOP DELIVERY

After the user's identity is verified, policies controlling the user's environment are applied. These policies specify what actions a user is allowed to perform, what resources he is allowed to use, what program functions are available etc. For instance, a user may not be restricted from printing or from uploading files if they connect from a home Pc.

The desktop environment is then delivered to the client using the Independent Computing Architecture (ICA) and Remote Desktop Protocol (RDP).

OTHER PROCESSES

There are other sub-processes or modules that are part of a Citrix XenDesktop system.

WAN optimization: The clients may not be in the same bUilding as the data center. In this case, WAN optimization is required for those who log in from remote locations like branch offices or from home. WAN optimization employs special technology to prioritize different parts of the user experience, to ensure Quality of Service (QoS). For instance, it ensures that network performance does not degrade when a user chooses to send a large file or print job over the network. This optimization is done by the Citrix Access Gateway module.



Monitoring: IT administrators need to know how resources are being utilized and they need to monitor the 'health' of the virtual desktop hosting infrastructure. The Citrix Edgesight module analyzes and troubleshoots issues as well as warns IT administrators in advance when issues may arise.

Secure Delivery: If clients are outside the corporate firewall, then images of the desktop and other data that's being exchanged need to be secured. XenDesktop secures these connections via ssL by using Citrix's Access Gateway technology The Access Gateway is a hardened appliance deployed in the corporate DMZ which allows ssL-encrypted XenDesktop connections to traverse the corporate firewall securely. Support systems: Users are typically dispersed and work from offices at different

Support systems: Users are typically dispersed and work from offices at different locations. They may not have access to IT support staff To address this, XenDesktop incorporates Citrix GoToAssist, allowing support staff to remotely support XenDesktop users. There's also Citrix EasyCal1 technology that allows users to initiate a call to tech support from their desktop (by simply moving their mouse over any phone number) and have it connect the call between the corporate PBX and any phone that's nearby.

There are a number of hardware and software components at the data center level. Essentially, there are blade PCs, servers and software to manage the infrastructure and the virtual machines.

BLADE PCS OR WORKSTATIONS

A blade PC plugs into a rack enclosure and it can be easily replaced"The blade has a processor, memory and hard disk and it may also have a graphics sub-system. However" it does not host the as, applications or user,documents as these are stored centrally. Blade workstations handle more resource intensive tasks.

BLADE MANAGEMENT

Resources have to be deployed for each blade. The health of the blades has to be monitored. When a blade fails it must be shut down and then restarted. These are typical tasks handled by blade management software like HP Insight Control.

VIRTUALIZATION SOFTWARE

Software such as VMware and Citrix XenDesktop create a virtualization layer to host all the virtual desktops or virtual machines (VMs). VMs are software implementations of a computer.

ACTIVE DIRECTORY

This is a directory service that maintains a list of all the network resources, and maps these to their respective network (IP) addresses.

STORAGE

Storage is certtralzed and space is allocated to users depending on their profiles. There is a choice of storage solutions and architectures such as Direct Attached Storage (DAs), Network Attached Storage (NAs), Internet SCSI (iSCSl), and fiber channel Storage Area Networks (SAN).