I’ve been working with Citrix products pretty much as long as there have been Citrix products, and one of the toughest questions to answer over the years has been, “Will my application run in a Citrix [usually meaning XenApp] environment?” Often, the answer was, “Ummm…..maybe, but we need to test it.”
Back in the bad old days of DOS and the first few revs of Windows, programmers could get away with taking shortcuts like talking directly to hardware peripherals without using the proper APIs – in fact they could make things run faster on the limited hardware of the day by doing so. But as we moved forward into NT-based execution platforms and multi-user server operating systems, those programming shortcuts played holy you-know-what with application compatibility.
As time went on, more and more of those applications either died off or got re-written to comply with the proper programming conventions. But for a long time you would still find applications that were mostly well-written…but they had shortcomings like hard-coded UNC paths. They might, for example, create some kind of temporary “scratch” file in C:TEMP, which may be just fine on a single-user PC, but is not fine at all on a Terminal Server that’s supporting 40 or 50 concurrent users, all of whom are trying to write to that file in the C:TEMP directory and overwriting (or corrupting) one another’s data.
Sometimes a good “Citrix mechanic” could figure out what was going wrong, and manually tweak something (often in the Windows registry, which is not for the faint of heart) that would allow the application to play nicely in a multi-user environment. Over the years, the engineers I’ve worked with were able to make some applications work when their own manufacturers said it couldn’t be done. More recently, application virtualization tools such as Microsoft’s App-V, or the packaging and streaming tool included with XenApp, have made it easier to do things like redirect hard-coded paths to user-specific paths.
We finally reached the point where most 32-bit Windows applications would run just fine in a Terminal Services/XenApp environment, although some manufacturers still won’t support running their applications this way, probably because they don’t want to go to the extra effort of testing and certification. (You know who you are.)
But now we have a whole new level of potential incompatibility: 64-bit execution. Windows Server 2008 R2 is 64-bit only. The latest version of XenApp, v6.0, is designed specifically for 2008 R2. It’s a safe bet that there will never be another 32-bit version of Windows Server, so this is our new reality. And we’re finding that some apps that ran fine under Windows 2003 Terminal Services, and even on 32-bit Windows 2008 platforms, won’t run on 2008 R2. (And don’t even get me started about printing – that’s a whole discussion of its own!)
The good news is that there are a couple of Web resources out there that are devoted to answering the question, “Will my application run?” The first is the Microsoft Remote Desktop Services Community Verified Compatibility Center. You’ll find separate sections there for Server 2003, 2008, and 2008 R2. The other site is the Citrix Ready Community Verified site. There you will find information on over 4,000 third-party products including both hardware and software.
Of course, I can’t guarantee that you’re going to find your app listed on either site. But the odds are a heck of a lot higher than they were a few years ago, and that’s a very good thing.