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Before creating an image of a XenApp server, several steps must be performed to generalize the XenApp installation, in order to remove the machine-specific information from the install and allow the server to come online and join the XenApp farm as a unique entity. In the past, this was either accomplished manually or through the use of a set of scripts. Citrix has since released a small MSI that contains a command-line tool and a Windows service that can be leveraged to quickly generalize a XenApp installation. The tool is called XenAppPrep and it can basically be thought of as the equivalent of sysprep for Windows, only used with XenApp installations.

With XenAppPrep, you can easily prepare and clone your XenApp servers, either by traditional Ghost/image type methods or through the use of Provisioning Services (talked about in my previous post Citrix Provisioning Services Part 2 – PVS with XenApp!). Using XenAppPrep is a simple process:

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My last post Citrix Provisioning Services Part 1 – What Is It? served an introduction to what exactly Citrix Provisioning Services is capable of. Below I hope to open people’s eyes to using PVS for something other than VDI, as it is often thought of as a part of the XenDesktop suite. However PVS is actually independent of XD or VDI, and can be utilized in combination with XenApp to bring single-image benefits to the Terminal Services world.

Provisioning Services allows for server consistency, easier maintenance, dynamic servers, and aids in disaster recovery.

• Consistency – As a best practice every XenApp server delivering the same applications should be 100% identical to the rest of the farm. However, obtaining this is easier said than done.  By streaming the same image to every server, each server is inherently and 100% the same as the rest.
• Maintenance – Updating and patching large farms can be a very time consuming task, and anything done to one server must be repeated for the entire farm to maintain consistency. With PVS, patches and software installations are applied once to the master image and on next reboot, each XenApp server boots the new updated image. In addition to software patching and installation, Terminal Servers need to be completely refreshed periodically to keep them clean and performing optimally; they are used by dozens of different users, reducing performance and resulting in inconsistent servers. A typical server refresh requires the server to be re-imaged and the software redeployed, a time consuming process that can be prone to error, leaving a server in an unusable or inconsistent state. Operating system streaming with PVS results in a completely fresh and optimized server on every reboot.
• Dynamic – PVS allows for a dynamic XenApp farm instead of a static one. As load rises and additional servers are needed, they can be quickly brought online in seconds instead of hours. Conversely, as load drops, un-needed servers can be powered off or repurposed as needed. A server becomes a vessel for different workloads and can be a XenApp server one day and an IIS server another if need be. Since Provisioning Services is capable of streaming to both physical and virtual servers, administrators have the ability to utilize different types of resources all from the same master image(s).
• Disaster Recovery – Creating a disaster recovery plan for the XenApp environment often requires complex processes, scripts and configurations. Assuming a PVS server has been built in the DR site, and that the master image has been replicated as well, quickly bringing an entire farm of XenApp servers online becomes a simple task.

Creating a XenApp environment that is more dynamic and easier to maintain is a goal for many XenApp administrators. The addition of Provisioning Services to a XenApp implementation can go a long way to achieving those goals. By leveraging the single-image management capabilities of PVS, administrators can dramatically reduce the costs involved with deploying and maintaining their XenApp farms. While at the same time, guaranteeing consistency between and ensuring peak performance of each server in the farm. All while being capable of quickly adapting to changes in load and disaster scenarios.

One of the great features of desktop virtualization (VDI) being touted by the industry is the ability to manage and update all of your desktops from a single central master image.

Citrix’s solution to the single image process is accomplished by a product called Provisioning Services (PVS). This software is the result of their purchase of a company called Ardence back in 2007. Provisioning Services is an often misunderstood piece of software, and its great benefits and potential are not necessarily apparent to everyone.

PVS works by streaming a master (read-only) image from the server to a target server or workstation. Any subsequent writes are then sent back to the PVS server and written to a cache file. The reads and writes are sent back and forth between the PVS server and target in a constant stream over the network. The easiest way to grasp this is to imagine that the cable connecting the hard disk inside of the server to the motherboard (and thus the CPU and RAM) is replaced by a network cable running back to the PVS server. The operating system sees the PVS disk as though it were a normal hard disk, and everything is done entirely transparent to the OS. The magic happens when the server is powered up; instead of booting from a local disk it is instead set to boot to the network card (PXE, BOOTP) which talks to a service on the PVS server, which streams the assigned operating system image to the target. The target device starts up immediately, as though it was booting from a local disk.

The beauty here is that this single read-only image can be simultaneously streamed to multiple diskless targets, both physical and virtual. This central image can now be maintained in one place. This makes tasks such as installing updates or new software quick and easy. After installing an update into the master image, all machines running that image will boot up into the updated image on next restart. To put that in perspective, think of the time and effort required to push out something such as a service pack to Windows or Microsoft Office to your entire firm. Now imagine simply installing that update once and having every machine in your environment receive that update on next reboot, without any additional effort.

Look for a follow-up post discussing the benefits that Provisioning Services can bring to a XenApp implementation.