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About Virtualization Infrastructure

The virtualization infrastructure, which is the center of a XenApp deployment, concerns the following concepts:

Application enumeration

Application enumeration is when Citrix client software lists virtualized applications available on the XenApp servers. The client software transmits data to locate servers on the network and retrieves information about the published applications. For example, during enumeration, Citrix Receiver communicates through the Citrix XML Service with the XenApp server to determine applications available for that user. Application publishing To deliver an application to your users, whether virtualized on the desktop or the server, use the AppCenter to publish the application.

Citrix Licensing

A Citrix License Server is required for all XenApp deployments. Install the license server on either a shared or stand-alone server, depending on your farm’s size. After you install the license server, download the appropriate license files and add these to the license server.

Data Store

The data store is the database where servers store farm static information, such as configuration information about published applications, users, printers, and servers. Each server farm has a single data store.

Data Collector

A data collector is a server that hosts an in-memory database that maintains dynamic information about the servers in the zone, such as server loads, session status, published applications, users connected, and license usage. Data collectors receive incremental data updates and queries from servers within the zone. Data collectors relay information to all other data collectors in the farm. By default, the data collector is configured on the first server when you create the farm, and all other servers configured with the controller server mode have equal rights to become the data collector if the data collector fails. When the zone’s data collector fails, a data collector election occurs and another server takes over the data collector functionality. Farms determine the data collector based on the election preferences set for a server. Applications are typically not published on the data collector.


A zone is a grouping of XenApp servers that communicate with a common data collector. In large farms with multiple zones, each zone has a server designated as its data collector. Data collectors in farms with more than one zone function as communication gateways with the other zone data collectors. The data collector maintains all load and session information for the servers in its zone. All farms have at least one zone, even small ones. The fewest number of zones should be implemented, with one being optimal. Multiple zones are necessary only in large farms that span WANs.

Streaming Profiles

You can deliver applications to users by either virtualizing them on the desktop (streaming) or by virtualizing them on the server (hosting). If you are virtualizing applications on the desktop, either streaming to the client or server, create a streaming profile server in your environment. To virtualize applications on the desktop, you create profiles of the application and then store the profile on a file or Web server. The profile consists of the manifest file (.profile), which is an XML file that defines the profile, as well as the target files, a hash key file, the icons repository (Icondata.bin), and a scripts folder for pre-launch and post-exit scripts.

Receiver Storefront

Receiver Storefront authenticates users to XenDesktop sites and XenApp farms, enumerating and aggregating available desktops and applications into stores that users access through Citrix Receiver or a Web page. The Receiver Storefront database records details of resource subscriptions and shortcuts to enable synchronization of users' desktops and applications across their devices.

Web Interface

You can use the Web Interface in any environment where users access their applications using either Receiver or a Web browser. Install the Web Interface on a stand-alone computer; however, where resources are limited, the Web Interface can be collocated with other functions.

XenApp Web and XenApp Services Sites

XenApp Web and XenApp Services sites (formerly known as Access Platform and Program Neighborhood Agent Services sites, respectively) provide an interface to the server farm from the client device. When a user authenticates to a XenApp Web or XenApp Services site, either directly or through Receiver or the Access Gateway, the site:

  • Forwards the user’s credentials to the Citrix XML Service
  • Receives the set of applications available to that user by means of the XML Service
  • Displays the available applications to the user either through a Web page or by placing shortcuts directly on the user’s computer
Citrix streaming integrated architecture
Citrix XML Broker and the Web Interface

The Citrix XML Broker functions as an intermediary between the other servers in the farm and the Web Interface. When a user authenticates to the Web Interface, the XML Broker:

  • Receives the user’s credentials from the Web Interface and queries the server farm for a list of published applications that the user has permission to access. The XML Broker retrieves this application set from the Independent Management Architecture (IMA) system and returns it to the Web Interface.
  • Upon receiving the user’s request to launch an application, the broker locates the servers in the farm that host this application and identifies which of these is the optimal server to service this connection based on several factors. The XML Broker returns the address of this server to the Web Interface.

The XML Broker is a function of the Citrix XML Service. Only the XML Service on the server specified in the Web Interface functions as the broker. The server hosting the XML Broker must be configured with the controller XenApp server mode. In a small farm, the XML Broker is typically designated on a server dedicated to several infrastructure functions. In a large farm, the XML Broker might be configured on one or more dedicated servers.

The XML Broker is sometimes referred to as a Citrix XML Server or the Citrix XML Service. For clarity, the term XML Broker is used to refer to when the XML Service functions as the intermediary between the Web Interface and the IMA service, regardless of whether it is hosted on a dedicated server or collocated with other functions.

Application delivery

XenApp offers three methods for delivering applications to user devices:

  • Server-side application virtualization: Applications run on the XenApp servers. XenApp shows the application interface on the user device or client, and transmits user actions from the device, such as keystrokes and mouse actions, back to the application.
  • Client-side application virtualization: XenApp streams applications on demand to the user device from the XenApp farm and runs the application on the user device.
  • VM hosted application virtualization: Challenging applications or those requiring specific operating systems run inside a desktop on the XenApp server. XenApp shows the application interface on the user device or client, and transmits user actions from the device back to the application.


qfarm -d     #run on XenApp server to show data collector
qfarm -load   #run on Data Collector to show current load in the current farm zone
eventviewer.exe - run on a data collector, search for entry who triggered the election