Here we are again, for another Provisioning Services for XenApp Best Practice.  This best practice focuses on integrating applications into the vDisk image.  Pretty simple Yes or No answer.

But this is one of the major challenges with creating a base XenApp image is determining what to include and what not to include.  Of course, you need the operating system and XenApp and Provisioning Services tools, but beyond that what is recommended and why?  Take the following scenario: due to business reasons, an environment has three sets of XenApp servers hosting different line-of-business applications.  All three line-of-business applications are dependent on Microsoft Excel for viewing and editing integrated spreadsheets.  Should Microsoft Excel be part of the base image or should it be a streamed application?  There answer is… there is no right or wrong answer; it is all dependent on other factors within the environment. Don’t you just love answers like that?

The decision to include core applications is oftentimes a result in the belief that the base image should contain the greatest number of items that are common between XenApp servers.  If every server requires the same application, more network bandwidth will be used when the application is streamed to every server as part of the application streaming process.  Also, application streaming, in the default configuration, does not initially start as fast as a previously installed application because the application must be sent across the wire.  Thus, users will experience latency while the application is streamed for the first time (this latency can be overcome with application pre-caching, as explained in the Application Cache section).

There is also a business aspect to this decision. In some organizations, one set of administrators is responsible for applications and another set is responsible for the XenApp configuration. By separating the applications from the base image, the technical solution can align more closely with the organizational structure of the business.

Base Image Application Inclusion
Base Image Application Exclusion
  • Base image and applications included in a single server role, which will allow for the fastest rebuild and delivery times. * Less network bandwidth is used because the applications are already present in the base image and no additional installations are required.  The complete image can be deployed during off hours so as to not impact availability of the XenApp servers during the day.  * Application startup time is shorter because the application is already part of the image and does not need to be streamed.
  •  With fewer items included in the base image, maintaining the image is easier as only the core operating system and XenApp are provisioned initially.* XenApp base images are managed with one set of tools, and applications and corresponding updates are managed with a different set of tools.  This makes it easier to have multiple administrators responsible for different areas of expertise. * XenApp silos become a thing of the past. A single XenApp server image can be used to deliver any application at anytime.  A single image to maintain for the entire XenApp farm greatly simplifies support
  • Core application versioning changes can impact the base image.  For example, if all servers require the same version of Microsoft Excel, no issues are raised.   However, when individual application upgrades occur, some applications might require Excel 2007 while others require an older version. This would have a profound impact on the contents of the base image.
  • Modifying an application within an image will impact all servers that rely on the image. This might require different levels of change control for applications that are integrated with the base image and applications that are not integrated.
  • More images to maintain, which can make support more difficult, although the number of Provisioning Services images is still far fewer than the number of images required for other server build solutions
  • Streaming applications will increase network utilization during startup, although this can be mitigated with application pre-caching. 
  • In the default configuration, the first user starting an application will notice a pause before application startup as the application is streamed to the server.  This can be overcome with application pre-caching.
  • Not every application can be streamed. Although XenApp streaming has improved to include more applications, there are some that cannot be streamed because they require special functionality

Regardless of the decision on which applications to include and exclude in the base image, the following are general best practices for the base image:

  • All relevant operating system and XenApp hotfixes and service packs should be included in the base image.
  • The most common operating system and XenApp configuration should be used for the base image. If 80% of the servers require a specific setting while another 20% do not, the base image should include the special setting.
  • The base image should include all appropriate XenApp plugins.  If application streaming will be used, the streaming plugin should be installed as part of the base image.
  • Depending on the usage of server certificates, the appropriate root certificate should be part of the base image.  

What do all of you think? Do you install the common applications into the base vDisk, or do you rely on XenApp application streaming? How many unique XenApp images do you have in your environments? 

As always, stay tuned for more best practices regarding Provisioning Services and XenApp.  

  • vDisk Type
  • vDisk Cache
  • Active Directory
  • Application Integration
  • Application Streaming Cache
  • System-level settings: Page file, drive remapping and multiple drives
  • Image Management
  • Local Database Storage (event viewer, EdgeSight, AntiVirus updates)
  • Plus more if we get some good ideas on other areas of focus.

Daniel – Sr. Architect
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