Concepts of XenApp 5 from Citrix E-docs

Farm Terminology and Concepts Terminology

The XenApp planning and installation documentation uses the following terminology.

Multi-user environment
An environment, including XenApp and Terminal Services, where applications are published on servers for use by multiple users simultaneously.
Application servers
The farm servers that host published applications.
Infrastructure servers
The farm servers that host services such as the data store or the license server. Typically, they do not host published applications.
Production farm
A farm that is in regular use and accessed by users.
Design validation farm
A farm that is set up in a laboratory environment, typically as the design or blueprint for the production farm.
Pilot farm
A preproduction pilot farm used to test a farm design before deploying the farm across the organization. A true pilot is based on access by select users, and then adding users until all users access the farm for their everyday needs.
The process in which a client transmits data to locate servers on the network and retrieves information about the server farm’s published applications. For example, during enumeration, the XenApp Plug-in for Hosted Apps communicates with the Citrix XML Service or the ICA browser, depending on the browsing protocol selected in the plug-in.

XenApp Setup comprises two installation wizards:

Create a New Farm. The first time you install XenApp, select Create a New Farm in the installation wizard and Setup creates the farm with that server hosting specific roles.

The server where you installed XenApp and created the farm is the first farm server or the Create farm server.
Join an Existing Farm. When you run Setup on servers after installing XenApp on the first farm server, you take a different path in Setup and XenApp references the settings you specified on the first farm server. These servers join the existing farm and communicate with the first server in the farm.

Farm Environment

You should already be familiar with client-server architecture, redirection, and application publishing.

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 first server in the farm functions as the data collector.
By default, the data collector is configured on the first farm server during the Create Farm Setup and all other servers are configured with 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
The data collector is an infrastructure server and applications are typically not published on it.
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 File or Web Server
Applications can be delivered to users by either streaming or hosting the applications on the server. If you are streaming applications, either to client or server, you must install a streaming file server in your environment. When streaming applications, 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 CAB files, a hash key file, the icons repository (Icondata.bin), and a scripts folder for pre-launch and post-exit scripts.
Web Interface
The Web Interface is a required component in any environment where users access their applications using either the XenApp plugin or a Web browser. Install the Web Interface on a stand-alone computer; however, where resources are limited, the Web Interface is sometimes 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 the XenApp plug-in 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 XML Service and the Citrix XML Broker
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. By default, the XML Service is installed on every server during XenApp Setup. However, only the XML Service on the server specified in the Web Interface functions as the broker. (The XML Service on other farm servers is still running but is not used for servicing end-user connections.) 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 infrastructure functions.

This illustration uses a large farm to show how the Web Interface and the XML Broker work together. (1) The user connects to the Web Interface through the XenApp plug-in or a Web browser; (2) the Web Interface contacts the XML Broker to determine which applications are available for this user; (3) the XML Broker queries the IMA service for this information and returns the results to the Web Interface; (4) the Web Interface displays the available applications to the user either through a Web page or by placing shortcuts directly on the user’s computer..

Infrastructure Servers
XenApp farms have two types of servers: infrastructure servers and member servers that host published applications. Infrastructure servers perform specific functions and do not typically host published applications, except in small farms. The services include:

Farm infrastructure services – Data store, data collector, and the Citrix XML Broker.
Access infrastructure services – Web Interface, Secure Gateway (optional), and Access Gateway (optional).
Additional services – Citrix License Server, Streaming File or Web Server (optional), a computer for profiling applications, Configuration Logging database (optional), EdgeSight database (optional), and SmartAuditor player (optional).

One or more infrastructure services can be grouped together in small farms. In large deployments, each service runs on one or more dedicated servers.
This illustration suggests which infrastructure functions can be grouped on the same server, depending on the size of your environment.

Factors other than size can affect how infrastructure functions are grouped . Security concerns, virtualized servers, and user load play a part in determining which functions can be collocated.
This illustration depicts infrastructure servers in a large farm. The Web Interface, XML Service, data collector, and data store are deployed on separate servers.

source: XenApp 5 for Windows Server 2008 – E-Docs
Note: This link has also several great illustrations of the components of XenApp. If you learn visually like I do you must see these illustrations

XML Port and SSL Question
Dan Murray made a interesting comment on XML and SSL
You need to do three things… you have to install a certificate on the server that is handling the XML requests, typically a Zone Data Collector in a XenApp farm, or a DesktopDelivery Controller in a XenDesktop farm. Next, setup the SSL Relay on that ZDC/DDC server. Finally, you have to configure the WI XML port to use SSL. You need all three pieces to be working to use SSL across the board the way you want to


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