Once those hurdles have been overcome, the meat of a XenApp installation can be deployed. This generally consists of a Web server running IIS or Apache, a license server, some number of XenApp farm servers, and perhaps Citrix's XenDesktop VDI product. Creating this infrastructure isn't terribly difficult once you know how everything fits together, but it's certainly not a task for the uninitiated. Proper training is a fundamental requirement of any XenApp project.
The IIS or Apache Web services layer, running on a specific server or set of servers, communicates with the XenApp server farm to handle load balancing, application delivery, authentication, and authorization. It's the linchpin of the overall solution. It serves up an attractive Web portal for users to log in and gain access to their desktop or their applications from any Web browser, and it handles the background communications for users running Citrix Receiver.
This service communicates with the farm, composed of dedicated application servers running Windows Server 2003 or Windows Server 2008. The first-built server in the farm is the de facto data store server, which either houses the data locally (for small installations) or communicates with a Microsoft SQL Server instance that handles that particular load. Either way, building and adding to a XenApp farm is relatively simple, once you've cut through the list of dependencies for each farm server. Perhaps the simplest way to construct a XenApp farm is to virtualize the farm servers and use pre-built templates to deploy new servers as needed. It can take several hours to build a farm server from scratch, with most of that time taken by the Windows Server install and all the associated requirements.
Once that's done, however, the solution generally Just Works. Simply point a client to the Web services host and log in.
Terminal Services tax
Licensing for XenApp isn't terribly difficult, but licensing for Microsoft Terminal Services can be. For every seat that will access a XenApp server-hosted application or desktop, a Microsoft Terminal Services CAL is required. There are myriad dependencies on how much these CALs cost, including the type and version of the client OS, volume licensing deals, and others. It's best to fully investigate these costs prior to embarking on any Terminal Services or XenApp projects.
As for XenApp licensing itself, XenApp Platinum costs $600 per seat with a one-year software subscription. Subsequent subscription renewals cost $75 per seat. XenApp Enterprise runs $450 per seat with $50 subscription renewals, and Advanced can be had for $350 per seat and $45 subscription renewals. There are other plans for smaller installations.
Citrix XenApp isn't right for every infrastructure, but with the addition of features like application streaming (which arrived in version 4.5) and VM-hosted applications (newly available in XenApp 5 Feature Pack 2), it is certainly right for more of them. Like just about any IT endeavor, implementing application virtualization requires proper prior planning and a skilled hand on the tiller, but armed with those tools, it can be a powerful solution to many of IT's desktop delivery problems.
Bottom Line
Citrix XenApp 5 Feature Pack 2, the latest version of Citrix's flagship application virtualization product, offers a host of new features to ease both user and administrative interactions. Simply put, Citrix XenApp is arguably the best example of centralized desktop computing available.