Remote Desktop Services (RDS) from Microsoft is an essential platform and a requirement for app virtualization via Citrix XenApp. It is a role in Windows 2012 Server that enables users to share a physical or virtual desktop located in the data center over the network via the Microsoft proprietary RDP protocol. Every user in an RDS environment needs an RDS license in order to use a remote desktop or application. RDS licensing can be per user or per device. These are also known as Client Access Licenses (CALs). Commonly, organizations employ a per user license, which allows one user to have access to all the instances of a particular product (for example, RD hosts), while device licenses make sense in an environment where multiple users connect to a single RD Host from the same computer (for example, shift workers using kiosks, and so on). So, you may find yourself wondering why you need Citrix in the first place when you can deliver remote apps and desktops to your users by simply configuring RDS on a Windows 2012 server. A lot has been said about the two products and the main arguments in favor of Citrix XenApp are the level of granularity involved in configuring and administering the environment, the security of the Citrix proprietary Independent Computing Architecture (ICA) protocol, and the endpoint device support. Currently, 95% of Fortune 500 companies use XenApp to deliver applications and desktops to their end users, and Citrix has been focused on developing its virtualization portfolio for well over a decade with cloud networking and mobility products recently acquired to complete the circle of workspace transformation.

XenApp 7.6 (formerly known as Presentation Server, MetaFrame, and WinFrame) is an application virtualization software built to deliver a secure and highly-customizable set of applications and desktops to end users regardless of their location or endpoint device type. XenApp's Virtual Delivery Agent (VDA) is installed on an RDS-enabled Windows Server OS, while the XenApp environment (also known as a farm or site) is managed by a Delivery Controller installed on a separate non-RDS Windows server. The applications can be installed on the XenApp VDA server, and a client software called Citrix Receiver needs to be deployed on the user's endpoint device to enable application launching. We will explore the XenApp architecture in further detail in Chapter 2, Designing a Citrix^® Solution to Fit Your Needs, but, for now, it is important to remember (much like other enterprise software) that there is a management component (also known as a controller or broker) and a delivery agent. The communication between the two is vital for an operational environment. The following diagram illustrates the conceptual architecture of XenApp:

The XenApp conceptual architecture available at http://www.citrix.com/. © Citrix Systems, Inc.

XenApp 7.6 uses a proprietary Citrix communication protocol called ICA. ICA transmits data intercepted by XenApp from an application running on the server to the Citrix Receiver on the client device over standard network protocols, such as TCP/IP and, formerly, IPX/SPX. From the client side, when a user interacts with the application (for example, a mouse movement or keyboard input), the Receiver software on the client device circulates the traffic back to the application running on the XenApp server. Multiple virtual channels exist within the ICA protocol, such as multimedia, printing, USBs, smart cards, and others. These virtual channels define various functions within the ICA stream and different settings can be applied to control their impact based on the requirements of the environment. In Chapter 11, Administering a XenApp^® Environment – Server Management, we will go into further details regarding Citrix group policies that can be implemented to manage application security and user experience. The following diagram illustrates the ICA protocol and virtual channels:

ICA protocol and virtual channels available at http://www.support.citrix.com. © Citrix Systems, Inc.

Citrix XenApp 7.6 uses the FlexCast Management Architecture (FMA), which is conceptually the same model used by Citrix XenDesktop. In fact, in 2013, Citrix merged the XenApp and XenDesktop technologies into a single delivery platform under the umbrella of XenDesktop 7.0. Starting with XenDesktop 7.0, you could deliver both applications and Virtual Desktop Infrastructure (VDI) from a single pane of glass. However, less than a year later, Citrix reintroduced XenApp as a standalone licensed product, which once again used the same integrated management model as XenDesktop FMA. You do not have to purchase XenDesktop licenses in order to use XenApp. The latter can also be deployed on both virtual machines and physical servers depending on the nature of the existing infrastructure.

In this section, we will explore the user logon process in XenApp in a hosted app scenario. As explained earlier, the true power of XenApp is that a user can launch a variety of remote applications running in a server environment at any time on any device. This is a brief overview of how the traditional logon process in XenApp 7.6 works:

Now, let's take a look at how the Citrix infrastructure makes the aforementioned transaction possible on the backend:

An entire book can be written on licensing a Citrix environment, its underlying components, and how to make the best decision on what license to purchase. To sum up, three product editions are available for XenApp—Advanced, Enterprise, and Platinum. Advanced offers a basic set of features required to build an application virtualization solution, such as the ability to publish apps and desktops. Enterprise and Platinum provide a rich set of functionalities, such as image management via PVS and comprehensive monitoring tools that are needed to operate a large environment with business-critical applications and no fault tolerance.

It is important to note that the XenDesktop Enterprise and Platinum editions include XenApp, so if you were to purchase XenDesktop, you would have the flexibility to publish applications and shared desktops as well as dedicated end-user OSes. XenApp licensing is based on a session concurrency model where each user needs to be granted a license when a session (running application) is initiated. This license is returned to the license pool when a session terminates. The next time the same user launches an application, they are granted a new license. In other words, a license is not permanently tied to a user or a device, but is rather granted for the current session only.

After purchasing Citrix licenses, license files need to be installed on a Citrix license server version 11.12, which can reside on a Windows 2008 or 2012 OS, and it is also available as a Linux-based VPX (virtual appliance) imported directly to the hypervisor. The license service software can be downloaded from http://www.citrix.com/. During the first deployment presented by this book, you will learn how to work with Citrix license files and troubleshoot a Citrix licensing component.

Most big vendors have a licensing structure that is often times a bit more complicated and cumbersome than we would like it to be. Furthermore, it can lead to unnecessary costs if not carefully analyzed upfront. Microsoft is no exception and the combination with Citrix can sometimes cause confusion as to what type of licenses are needed to build a new XenApp environment or expand existing systems. For Citrix to work on Windows, you will need to license two components—the operating system and Remote Desktop Services (RDS). Here is a list of licensing options from Microsoft that support virtualization at the time of writing this book:

With regard to an OS, today, many companies use a Key Management Service (KMS) server to manage the volume licensing of their enterprises. KMS is supported by Citrix as a central licensing authority for Windows and Office and is by far the most popular method for license activation. It is always beneficial to have a conversation with your Microsoft sales representative or a Microsoft reseller to ensure that you get the best licensing mix for your budget.

The purpose of this book is to build and showcase an enterprise-ready Citrix solution. As such, other Citrix products and components will also be involved in the implementation. For example, Citrix StoreFront is a component of XenApp and XenDesktop that presents users with the Receiver store or website where they can subscribe to their applications. StoreFront, which is a required component, is part of the XenApp installation media and needs to be installed on an IIS-enabled server.

In Chapter 6, Installing and Configuring NetScaler Gateway™, and Chapter 7, Load Balancing XenApp^® with Citrix^® NetScaler^®, you will learn how to implement load balancing with Citrix NetScaler VPX, and how to frontend your XenApp environment with NetScaler Gateway. NetScaler is a multipurpose appliance developed by Citrix and is widely used for load balancing backend server connections on a variety of communication protocols, such as HTTP, SSL, and FTP and other functions, such as network security and traffic optimization. In fact, NetScaler is such an enormous platform that a dozen books have been written about it. If you would like to dive deeper into full-blown enterprise implementations of NetScaler, I personally recommend you to go through Implementing NetScaler VPXTM, Marius Sandbu, Packt Publishing. My book only focuses on what is necessary to build a basic load balancer and gateway and no advanced configurations are covered. NetScaler is not required for XenApp to function properly. However, load balancing your StoreFront (Web) servers is highly recommended in a production environment, which is why it is included in this book.

In Chapter 9, Building Your First XenApp^® Farm – Provisioning Services™, you will learn about Citrix Provisioning Services (PVS). PVS is an enterprise-ready UDP-based streaming technology that is designed to deliver an OS over a network to the Preboot eXecution Environment (PXE)-enabled physical or virtual clients. At this time, PVS is included with XenApp Enterprise and Platinum editions and it can be leveraged for the provisioning of XenApp servers from a single virtual disk providing tremendous scalability over traditional standalone machine deployment.

In Chapter 4, Installing and Configuring Citrix XenApp^®, you will learn about Citrix Universal Profile Management. UPM is another add-on product for XenApp and XenDesktop that Citrix offers in order to facilitate integration of user profiles. UPM can be used instead of Microsoft roaming or mandatory profiles and a rich set of group policies is available through an Administrative (ADM) template to enforce granular profile settings. UPM also works in conjunction with Microsoft Folder Redirection, which can come in handy if your environment requires user files to be stored in a separate location from the profile.

Most paid software nowadays have some type of support agreement to provide technical resources to customers in case issues are experienced with the product itself or as a result of its operations. Vendors generally offer phone support, e-mail, newsletters, whitepapers, and even on-site assistance for critical issues. Typically, Enterprise Technical Support is subscription-based and there is an annual fee associated with the contract. Citrix provides different levels of support agreements. At the time of writing this book, Premier Support has gained a lot of popularity due to their 24x7 phone assistance and unlimited tickets. It is recommended that you engage your Citrix sales representative or an authorized reseller to get the most up-to-date information on technical support.

Each Citrix product version has an end-of-life (EOL) and end-of-maintenance (EOM) date. EOM is when a product is no longer maintained by developers, but you can still get assistance from a technician. EOL is when technical support is no longer offered for a particular version, and you are strongly encouraged to upgrade your software to the next supported version. Some product editions have end-of-extended-support (EOES) dates after the EOL, so if you have an extended support contract with Citrix, you will continue to receive assistance until EOES is met. Currently, XenApp 7.x (all subversions of 7) is maintained and supported until June 30, 2018. The following screenshot illustrates the XenApp product supportability matrix:

The XenApp product supportability matrix available at http://www.citrix.com/support/product-lifecycle/product-matrix.html. © Citrix Systems, Inc.

IT certifications have become an important part of the career development of IT professionals. A recent study conducted by InformationWeek showed that IT managers listed certifications as two and a half times more valuable than an MBA degree. Recent evidence shows that a certified professional can make up to a 40% higher salary than their noncertified counterpart. Many administrators, engineers, and consultants seek to obtain a Citrix certification as proof of technical proficiency in the Citrix stack. At the time of writing this book, Citrix has recently completed an overhaul of their previous exam structure.

Currently, three certification paths are available to customers—Apps and desktops (virtualization), networking, and mobility. The virtualization suite includes three certification exams—Citrix Certified Associate (CCA-V), Citrix Certified Professional (CCP-V), and Citrix Certified Expert (CCE-V). The CCE-V certification is an architect-level certification that validates the ability to design and implement enterprise systems based on XenApp and XenDesktop 7.x. Obtaining a Citrix certification can greatly increase job security and influence career advancement.

In this chapter, you learned the fundamentals of virtualization from both the hardware and application perspective. With regard to hardware, we took a hypothetical example to demonstrate the benefits of virtualization and learned how to differentiate between Type-1 and Type-2 hypervisors. From an application and desktop standpoint, we introduced two major platforms that work together—Microsoft RDS and Citrix XenApp. The latter was classified into three categories—hosted applications, streamed applications, and hosted shared desktops followed by a brief summary of desktop OS virtualization with Citrix XenDesktop. We also explored a user logon process in XenApp as seen by the user and as executed on the server. On the vast topic of licensing, we explained current offerings from Microsoft and Citrix in terms of OSes, RDS, and XenApp as well as benefits derived from various product editions. Required components, such as StoreFront for web access, and recommended options for load balancing and external authentication, such as NetScaler and NetScaler Gateway, were reviewed and more content will follow as they become more relevant in later chapters. From the supportability point of view, we looked at the lifespan of XenApp and the maintenance duration and current vendor support offered by Citrix. Last but not least, we provided insight on Citrix certifications paths to help you solidify your Citrix skillset and advance your career.

To sum up, we briefly touched on the high-level aspects of the XenApp software, its requirements, and its use cases.

In the next chapter, we will analyze some use cases from real-world field implementations. As we enter the design phase, we will start laying the foundation of our XenApp solution. Stay tuned...