IT can generate multiple virtual desktops from a single golden image, but that makes it even more important to...
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manage a base image correctly.
The base image for a virtual desktop deployment lives on a virtual machine in the data center, usually on virtual hard disks or virtual machine disk files. VDI image management tends to be straightforward, but each company's platform -- from VMware and Citrix to midmarket VDI vendors -- has its own rules and best practices governing image management. The key to managing base images for a VDI deployment is to understand the rules and limitations put in place by the vendor.
What is a base virtual desktop image?
The base image for a virtual desktop deployment is sometimes referred to as the master or golden image. A VDI golden image is an organization's standard desktop configuration. It contains an operating system (OS) and hardware configuration. In the case of a Windows-based image, IT can use the Microsoft Sysprep tool to allow VDI administrators to clone the OS. Typically, the base image also contains OS patches and even applications, but IT can also virtualize applications separately.
IT configures golden images to adhere to corporate security and compliance requirements, which means the virtual desktops the base image generates adhere to those policies too.
In some organizations, there is no standard corporate desktop configuration. For instance, a human resources department's desktops might require extra security, or an arts department might need desktops with more memory and processing power to support graphics-heavy applications. As a result, it is common for VDI shops to maintain multiple golden images. As a best practice, IT should limit the number of golden images, because the operational workload that VDI image management requires increases correspondingly as the number of base images increases.
As IT creates VDI base images, it is important to understand that vendors such as Citrix, VMware and Microsoft typically have a set of requirements that images must meet. The conditions might pertain to the desktop OS or to the virtual desktop's hardware configuration. For example, Microsoft requires its virtual desktops to include a virtual hard disk to store files and folders and at least 1 GB of RAM.
Managing and updating golden images
Citrix XenDesktop includes two options for image management: Provisioning Services (PVS) or Machine Creation Services (MCS), which is actually a component of XenDesktop that IT can access through the Studio management console. Because Citrix MCS is already part of the platform, it's easier for IT to use right away, but PVS' base image streaming technique allow admins to deploy hundreds of virtual desktops from a single golden image. VMware Horizon View shops can use the Horizon Mirage tool to update and manage separate, isolated layers of a golden image without affecting the entire image.
Managing golden images is a little bit trickier than deploying them because desktop OSes are not static. There is almost always a patch to apply or a configuration setting to change. Unfortunately, updating a master image usually doesn't also automatically update the virtual desktops based on the image.
When it comes to updating virtual desktops, remember that there are two main types: persistent and nonpersistent. Most virtual desktops are nonpersistent, which means the VDI software automatically resets the virtual desktop to a pristine state at the end of each user session. Persistent virtual desktops are dedicated to a specific user, so data and user settings remain from one session to the next.
Depending on which vendor's product a company uses, virtual desktops do not update by simply syncing the changes from the base image to the existing desktops. Instead, they regenerate. If IT makes a change to a golden image, it usually deletes its existing virtual desktops and then recreates them from the updated base image. It may not be possible to delete and recreate persistent virtual desktops in this way, however, because it would also erase users' data and settings. As a result, IT may have to update persistent virtual desktops individually.
IT can regenerate virtual desktops in a few different ways. Microsoft, for example, allows IT to force virtual desktops to update immediately, or at a scheduled time when most users are likely logged off. Because IT has to regenerate virtual desktops any time it updates a VDI golden image, many administrators try to minimize image updates by waiting to make several updates at a time.
The most important thing to remember is that testing is paramount. IT should thoroughly test updated golden images before they generate virtual desktops, because one mistake to the golden image applies to all the virtual desktops.
How VMware addresses VDI image management
Thirteen considerations for building a VDI golden image
Reasons a single image is not enough