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What Is Application Virtualization?

May 26, 2010 10:51 pm ⋅ 2 Comments ⋅

Some folks out there are still scratching their heads over the Citrix decision to change the name of Presentation Server to XenApp. There were actually several reasons for that change. For one thing, we’ve all seen Remote Desktop Services (formerly known as Terminal Services) get better and better with every release of Windows Server - and don’t think for a minute that Citrix didn’t see that coming. As closely as they work with Microsoft, of course they did. So it became obvious to Citrix long ago that they needed a better value proposition for their product than “something that I add to Terminal Services to get better performance.”

In point of fact, Citrix does have a considerably better value proposition than that - but not everyone was “getting it.” One way to help people get it is to re-frame the conversation by repositioning the product, and sometimes changing the product name can help make that happen.

But why XenApp? Well, that goes back to the acquisition of XenSource a few years ago. It seems that, after making that aquisition, Citrix decided that, in their vocabulary, “Xen” = “Virtualization.” Therefore…

  • “XenServer” = “Server Virtualization”
  • “XenDesktop” = “Desktop Virtualization”
  • “XenApp” = “Application Virtualization”

But does it, really? (XenApp, I mean.) Well, sort of. These days, application virtualization is a component of XenApp, but XenApp is more than just application virtualization.

Which brings me back to the question: What is application virtualization? I would suggest, as a good working definition, that, just as server virtualization is the abstraction of a server operating system from the underlying hardware, application virtualization is the abstraction of an application from the operating system it’s executing on.

We virtualize servers by interposing a layer of software – the hypervisor – between the hardware and the operating system. Although some operating systems, like Windows Server 2008, are virtualization-aware, meaning that they know when they’re running on a hypervisor and modify their behavior accordingly, earlier OS versions had to be fooled into thinking that they were running directly on server hardware when in fact they were not.

Applications today are still at the stage of development where they have to be fooled into thinking that they’ve been installed normally when in fact they have not. When they’re installed, applications typically write specific information to specific locations in the Windows registry. They place .DLL files into specific folders (most frequently into C:WindowsSystem32) – and sometimes these .DLL files overwrite or conflict with others, which is why you can’t, for example, run two different versions of Microsoft Access on the same PC workstation without some kind of application virtualization. Application virtualization places a sort of “software wrapper” around the application - sometimes referred to as an “isolation environment,” or a “sandbox.” It causes these Registry keys and files to be written to an application specific location, and redirects the application calls so they can be found when the application executes.

By contrast, when an application is executed via Remote Desktop Services (with or without the involvement of XenApp), you’re really virtualizing the presentation of the application. The application is executing on the server, and the user interface is being presented remotely at a client device, using a protocol such as RDP (Microsoft) or ICA (Citrix) to transport keystrokes and mouse movements from the client to the server, and screen updates from the server to the client.

In the old days – and often today as well – that application was installed directly on the Remote Desktop server. Today, we can instead use application virtualization to deliver the application to the server for execution on demand rather than installing the application in advance in the traditional way. But it’s important to understand that presentation virtualization – running the application in one place and displaying the user interface in another – is not the same thing as application virtualization, which, as we have defined it, has to do with how that application is installed on the desired execution platform and how it behaves when it executes.

The first product to do application virtualization on a large scale for Windows apps was Softricity, by a company called SoftGrid. Softricity evolved into App-V after Microsoft acquired SoftGrid. App-V not only virtualizes the application as described above, it also allows the application to be streamed on demand to the computer that needs to execute it. Application streaming works better than you might think, because it turns out that for most Windows apps, most of the code is seldom (if ever) used. (Just think of all the arcane features in Word or Excel that the average user will probably never use.) So we can stream down just enough code to get the user interface up and running, and continue to stream additional code in the background as features are actually required.

The combination of (1) not having to explicitly install applications on workstations (or Citrix servers, for that matter), and (2) not having to worry about applications conflicting with one another can make life much easier for the IT staff:

  • You no longer have to run around from workstation to workstation with a backpack full of installation CDs.
  • It can potentially eliminate the old practice of having multiple “silos” of servers within a Citrix server farm to run applications that would not play nicely with one another.
  • It makes image management for both workstations and XenApp servers much simpler, because if all of your applications are baked into your OS image, then any application change requires that you change (and regression test) your OS image - but if a streamed application changes, all you have to change is that application.

Meanwhile, back in Fort Lauderdale, Citrix had been working on its own approach to application isolation, which was added to the Enterprise and Platinum editions of Presentation Server when v4.0 was released. This “Application Isolation Environment” then evolved into application streaming with the release of Presentation Server v4.5. For those who are familiar with the Citrix application publishing paradigm, you can now:

  • Run the application through the Citrix packaging utility
  • Park the resulting package on a shared folder that’s accessible by your target machines
  • Step through the process of publishing the application, with a new twist: “I want to make this application available to this group of users, on this set of XenApp servers, and here’s the path to the application package.”

NOTE: Yes, I know that not all applications can be successfully packaged for streaming. But most modern Windows applications can be. Yes, you’ll have to test your apps, or, if you have a lot of apps, use a tool like AppDNA to analyze them for compatibility.

Administrative options allow you to specify whether an application package will be streamed to a XenApp server to be executed there, or streamed directly to the client PC to be executed there, or conditionally streamed (e.g., stream to the client PC if a particular set of criteria is satisfied, otherwise execute the app via XenApp). You can also stream it and cache it on the client PC so, in the case of a laptop, it can be disconnected from the network and continue to run the app for a specified period of time.

So, in a sense, the application virtualization component of XenApp competes with App-V. Prior to the release of XenApp 6, our advice would have been to use XenApp to package and stream apps if your need was primarily to serve up apps to Citrix users, and use App-V if Citrix represented only a small piece of your infrastructure and you primarily needed to package and stream apps to Windows-based workstations. This was mostly based on the fact that App-V needed its own servers to control publishing and streaming of the applications - so if your primary need was to deliver apps to XenApp users, it didn’t make sense to build that App-V control infrastructure when your Citrix farm already had everything you needed to stream apps via XenApp.

One of the features of XenApp 6, however, is the ability to deliver App-V packages through the Citrix application publishing infrastructure, without having to build out the App-V back-end server infrastructure. So now you can use whichever packaging tool you prefer with your Citrix infrastructure. If your staff is more familiar with - or just prefers - App-V, it’s not a problem, because XenApp will support those packages natively.

A discussion of application virtualization wouldn’t be complete without mentioning VMware’s ThinApp. A while back, VMware, seeing which way the competitive winds were blowing, realized it needed an application virtualization solution of its own, so it went out and bought one. In addition to packaging and streaming, ThinApp can also wrap an application up as a free-standing executable, meaning that you could theoretically carry the entire Microsoft Office suite with you on a USB stick, and plug it into any Windows PC anywhere regardless of whether (or which version of) Office was installed on that PC. Of course, if you actually did that with a PC that wasn’t already legally licensed for Office, you’re violating your Microsoft Office license, but I digress.

There are other application virtualization products in the marketplace, but at the moment, the “big three” are App-V, ThinApp, and XenApp. However, as I said way back in the beginning of this post, XenApp is more than just application virtualization. And that will be the subject of my next post.

Posted in: Application streaming, Application Virtualization, Citrix, Microsoft, Virtualization, VMware, XenApp ⋅ Tagged: , , , , , , , ,

What is Virtualization? - Application Virtualization

December 15, 2009 7:43 pm ⋅ 1 Comment ⋅

To continue the discussion of “What is Virtualization?” that I started back on December 4, I bring you the next installment - Application Virtualization.

Application Virtualization is the isolation and separation of an application from its underlying Operating System (OS) as well as from other applications. The application is fooled into believing that it is working as normal, interacting with the OS and using those resources as if the application had been installed directly on the OS as normal.

Additionally, the application can be installed once within the datacenter and preserved as a “golden image” to be delivered out to the end users. This gives you one instance to manage, one instance to patch, one instance to maintain - all housed in one location. This will help cut IT application maintenance costs as well as help control licensing costs as it will be easier to track application utilization.

Since each virtualized application is isolated from other applications it becomes possible to deploy, on the same piece of hardware, applications that typically didn’t play nicely together in the past. This cuts down on the time needed to test application compatibility since each application resides inside its own “bubble” (much like teenagers).application silos

Traditionally, both desktop admins and admins who were in charge of Terminal Servers (and XenApp servers) spent hours and hours on application compatibility testing. When a new application was added to the official desktop or server image, or an existing application was upgraded, regression testing was necessary to insure that the new or upgraded application didn’t break some other application by, for example, overwriting a shared DLL file. By providing a method for virtualizing Registry entries and calls to particular folder locations, application isolation overcomes most of these headaches.

The real trick with application virtualization is the delivery method, since the delivery methods of these virtual applications is what separates the different vendor solutions in this field. The big three application virtualization solutions are Citrix XenApp, VMware ThinApp, and Microsoft Application Virtualization (a.k.a. “App-V”). These three vendors use either one method or a combination of delivery methods to get the applications to the end users.

Application Streaming: This refers to streaming the application over the network to the client PC on demand. The “secret sauce” here is in figuring out how to stream down just enough of the code to launch the application and allow the user to begin interacting with it. The rest of the code can be streamed down when the user attempts to use a feature that requires it, or it can be simply streamed down in the background until all of the application code is cached locally. An added benefit of streaming all of the code down is that it allows the application to continue to be used when the PC is not connected to the network. (E.g., you can unplug your laptop and take it on the road.)

The application streaming technology you use will determine the control and security of the application once it has been streamed to the end user device. For example, Citrix allows you to administratively set a “time to live” limit on how long apps will run in a disconnected state. If the PC isn’t reconnected to the network within that time limit, the app simply stops working - giving you some level of protection if a PC is lost or stolen. For another example, ThinApp allows you to make an application completely portable - you could carry the Office Suite with you on a USB stick, plug it into any PC, use it, and leave no trace behind when you unplugged the USB stick. (Note: Doing this with the Office Suite could result in a violation of the Office EULA!)

Another “secret sauce” ingredient is the ability to allow limited communication between applications, even though they’re running in their own isolation environments (the “bubble” referred to earlier). For example, your accounting application may need to call Excel to render the output of a particular report. Early versions of application isolation required these applications to be “packaged” together, i.e., installed into the same isolation environment - otherwise, the accounting app wouldn’t know that Excel was available, and you’d get an application error. The latest implementations allow enough inter-isolation communication to take place to avoid problems like this while still avoiding application compatibility conflicts.

Application Hosting: This method can take a couple of different forms. The first is to virtualize the presentation of a typical Windows application by installing the application on a Terminal Server (in most cases, a Terminal Server with Citrix XenApp installed on it), and connecting to that Terminal Server using some kind of remote communications protocol (e.g., Microsoft’s RDP, Citrix’s ICA, etc.). We’ve been doing this for years, and thousands of customers and millions of users access applications this way every day.

Most readers of this blog are probably familiar with the advantages of this deployment model: centralized deployment and management, tighter security, granular control over what can be saved and/or printed at the client location, etc.

Application Streaming can work with this kind of Application Hosting by allowing you to stream applications to your Terminal Servers rather than having to explicitly install them or build them into your official server image. Citrix XenApp customers have the rights to use the Citrix streaming technology to do this, and Microsoft recently announced that the new Server 2008 R2 Remote Desktop Services CAL (formerly called a Terminal Services CAL) will include the rights to use App-V to stream applications to Terminal Servers.

Web-based applications can also be legitimately called “hosted applications” - whether they’re hosted in your own corporate data center, or by some kind of application service provider (e.g., Salesforce.com). In this scenario, all that’s required on the client PC is a browser - at least in theory.

In fact, the browser then becomes an application that must be managed! For example, you may find that you require a specific version of Java to access a particular hosted Web application - and if the user has local admin rights to the PC, the possibility exists that s/he will inadvertently install something that breaks its compatibility with your critical Web application. Some Microsoft applications require the use of Internet Explorer (e.g., Microsoft CRM is not compatible with Firefox). Some applications may even require a specific browser version. (When IE7 was first released, it caused compatibility issues for users of Microsoft CRM v3.0.)

Also, as a general rule, a Web application will require a more powerful client PC as well as more bandwidth between the client and the Web server to yield a good user experience, compared to an RDP or ICA client device connecting to a Terminal Server.

There is, of course, the option of installing an application directly on a device either by physically visiting the machine with installation media in hand or by using some kind of central management system to push the bits onto the client’s hard drive. These options, however, do not fall under the definition of application virtualization that we’re using here.

The important thing to take away from application virtualization is that no matter how you approach it, it will save you money:

  • Hardware – being able to host multiple applications on a single piece of hardware without worrying about application incompatibility. This can virtually eliminate the “silos” of servers with different configurations in large XenApp environments that used to be necessary to isolate those problem apps that wouldn’t play nicely with any others.
  • Licensing costs – with all your applications being housed in the data center you will have a better understanding of how many instances of each application you are using and will be able to better track your licensing needs
  • Maintenance – being able to update or patch a single instance of the application rather than needing to physically update and patch each machine.
  • Management – less hardware to look after, less time spent with helping end users with application issues, less time spent in application regression testing

Hope this clears up that “what is application virtualization” question. However if you have more questions feel free to use the comments or contact me directly.

Posted in: Application Hosting, Application streaming, Application Virtualization, General, Virtualization ⋅ Tagged: , , , , , , , , ,

Which App Streaming Is Best?

October 28, 2009 9:55 pm ⋅ Leave a Comment ⋅

For quite some time now, Citrix has had the ability to stream applications on demand, either to XenApp servers, or to desktop/laptop PCs. If you own current versions of XenApp, you can use it. Microsoft also has an application streaming product called App-V, which it evolved from its acquisition of Softricity a few years back. They recently announced that they were going to discontinue the App-V for Terminal Services licenses, and just bundle the rights into what is now (in Windows 2008 R2) called the Remote Desktop Services (“RDS”) CAL. So if you own Server 2008 TS CALs or 2008 R2 RDS CALs, you’ve got the rights to use App-V to stream apps to your Remote Desktop Servers a.k.a. Terminal Servers.

Not wanting to be left out of the application streaming game, VMware went shopping a while back, and bought ThinApp. They maintain that ThinApp is better - or at least safer - because it runs exclusively in user mode, whereas both App-V and Citrix App Streaming require the explicit installation of an agent that contains kernel components.

So what’s the real story? Which application streaming technology should you use? Which is really best? As is so often the case with IT, the answer is a resounding, “It depends.” It’s sometime frustrating, but the fact is that we work in an industry where there is often no single “right way” to do something. But today I ran across a blog entry over in the Citrix Community Blog area that did such a great job of delving into the differences that I thought it was worth linking to here.

Check it out and let us know what you think.

Posted in: Citrix, Microsoft, VMware ⋅ Tagged: , , , , , ,