by Chris Hampton

There are two primary methods of application virtualization in use across a growing number of vendors. The two methods can be categorized as agent-less and agent-based.

Agent-less application virtualization involves the use of an embedded virtual OS that is deployed as part of the virtualized application. These virtualized applications are fully encapsulated and able to run as a standalone executable from multiple locations such as a network drive, local drive, or USB drive.

Agent-based application virtualization utilizes a combination of a profiled or packaged application, a centralized delivery server, and a locally installed agent on the endpoint. The agents themselves utilize a kernel-mode driver or service. Some agent-based methods do not require the centralized delivery server and allow for shortcuts to be presented from a network share.

Both methods have the ability to stream the applications across the network to the local device. Streaming allows for immediate execution of the virtualized application from the endpoint while data blocks are streamed on-demand across the network or Internet. As the application is used, additional blocks will be streamed for the features required. The streaming of applications helps to minimize the network overhead required to run virtualized applications.

Comparison

Outside the obvious architectural differences of the two methods, there are a number of key management and performance differences that should be taken into account when selecting a specific vendor. Two of the key differences I would like to focus on are centralized management and user mode execution.

Centralized management is the use of a centralized delivery server. This server allows for the publishing of virtualized applications and setting access controls on the applications using Active Directory (AD) group security. The ability to set access security on virtualized applications is typically a base requirement for most organizations and should be considered when looking at application virtualization vendors.

Note: Some agent-less vendor solutions do allow for group-level security to be set when the application is packaged, although this option is not as dynamic as the centralized management option.

User mode execution is the execution of the virtualized application within the user-mode of the endpoint OS. The advantage to this architecture is that there is no interaction with the kernel of the endpoint’s OS, so if the virtualized application crashes, it will not affect the endpoint. Agent-based methods by their very nature utilize a kernel-mode driver and can cause an OS interruption if a virtualized application or agent were to crash.

Other Key Features to Look For

As you begin to shop around for your new shiny application virtualization solution, there are a few important features you should look for. I would consider these features to be very important for a well-rounded application and desktop virtualization initiative:

• Off-line usage – This feature allows virtualized applications to be launched even when the endpoint is disconnected from the network.
• Streaming over HTTPS – The ability to deliver virtualized applications over a secure SSL connection is vital in supporting a remote user base.
• Broad platform support – An important feature is the ability to run virtualized applications across a wide range of platforms including the option to deliver applications to a server-based computing environment.

About the Author

Chris Hampton, is a professional IT consultant based in Englewood, Colorado. With nearly 12 years in information technology, Chris has developed extensive experience in systems administration, engineering, and architecture specializing in VMware, Citrix, and Microsoft remote application and virtualization technologies. He has traveled extensively teaching for VMware. Chris has also contributed to the authorship of the recent The Authorized Guide to Citrix XenApp Platinum Edition (McGraw-Hill Publishers). He is currently working with the latest virtualization technologies on numerous consulting engagements. Chris holds some of the industry’s highest technical certifications from VMware, Citrix, and Microsoft in the areas of server-based computing and virtualization.