XenApp Architecture

XenApp architecture consists of:

• XenApp servers
• Web Interface servers
• Data collector
• Data Store database
• License server
• Worker groups

Single and Multiple Farm Environments
In single farm environments:

• All XenApp servers use the same data store
• Servers can be grouped into a single zone or multiple zones
• Applications can be load balanced across servers in farm

In multiple farm environments:

• Each farm has its own data store
• Applications can be load balanced across servers in farm, but not across multiple farms

Data Store
The Data Store database maintains farm data, including:

• Farm configuration information
• Published application configurations
• Server configurations
• Farm management security
• Printer configurations
• License Server name and port

The data store is the central repository where almost the entire Citrix implementation is invested. The Administrators of the farm, the license server to point to, the whole farm configuration, the published applications, all their properties, the security of who gets access to what, the custom load evaluators, custom policies, configured printers and print drivers, all this is stored in the central repository called the data store.

Data Store Updates and the Local Host Cache
 
The Local Host Cache contains information about:

• All the servers in the farm and their basic information
• All applications published in the farm and their properties
• All Windows network domain trust relationships within the farm 

The IMA service running on each Presentation Server downloads the information it needs from the central data store into a local MDB database called the local host cache, or “LHC.” (The location of the local host cache is specified via a DSN referenced in the registry of the Presentation Server, at HKLM\SOFTWARE\Citrix\IMA\LHCDatasource\DataSourceName. By default this is a file called “Imalhc.dsn” and is stored in the same place as MF20.dsn.)
Each Presentation Server is smart enough to only download information from the data store that is relevant to it, meaning that the local host cache is unique for every server.

Independent Management Architecture (IMA)
IMA a configuration database that holds all static data related to a server farm
Independent Management Architecture (IMA) is the underlying architecture used in Citrix Presentation Server for configuring, monitoring, and operating all Presentation Server functions. The IMA data store stores all Presentation Server configurations.
IMA runs on all servers in the farm. IMA subsystems communicate through messages passed by the IMA Service through default TCP ports 2512 and 2513.
The IMA Service starts automatically when a server is started. The IMA Service can be manually started or stopped through the operating system Services utility

IMA can be defined as a SERVICE, PROTOCAL and as a DATASTORE.
IMA Service: IMA Service is the central nervous system of Presentation Servers. This service is responsible for just about everything server-related, including tracking users, sessions, applications, licenses, and server load.
IMA Data store: Which stores Presentation server configuration information, such as published applications, total licenses, load balancing configuration, security rights, Administrator Accounts, Printer configuration, etc?
IMA Protocol: Which is used for transferring the ever-changing background information between Presentation servers, including server load, current users and connections, and licenses in use.
Ports used by IMA:
         2512: Used for Server to Server Communication
         2513: Used for CMC to Data store Communication


Data Collectors
A zone data collector is a server that manages dynamic information about the servers in the zone. Each farm has at least one zone
Server role, which is responsible of collecting all dynamic data within a server farm zone

 Data Collector Election
The data collector maintains dynamic data for servers in the zone. Therefore, each server must be able to contact the data collector for the zone.
If the data collector is unavailable, an election occurs and another server in the zone takes over the role of the data collector.
The process of taking the role is called Zone Data Colletor election. Server Administrators should choose the Zone Data Collector strategy carefully during the farm design itself. When an election needs to occur in a zone, the winner of the election is determined by

1. Highest version of Presentation Server first
2. Highest rank (as configured in the Management Console)
3. Highest Host ID number (Every server has a unique ID called Host ID).

  The data collector election process is not dependent on the data store. If the data collector goes down, sessions connected to other servers in the farm are unaffected .The data collector election process is triggered automatically without administrative interference. Existing as well as incoming users are not affected by the election process, as a new data collector is elected almost instantaneously.


Zones
A zone is a grouping of servers that share a common zone data collector.
A logical group of XenApp servers communicating with a single data collector is called a zone. Zones are typically
based on subnets.
Sharing data across zones can cause an increase in bandwidth consumption. As a best practice, keep the number of zones to a practical minimum. One zone is optimal

XenApp Components 
XenApp contains additional components to enhance the functionality of the solution, including the following:

• Load Manager
• Resource Manager (Powered by Citrix EdgeSight)
• Access Gateway VPX
• Citrix XenApp Provider
• Delivery Services Console
• License Administration Console  
• Citrix Plug-ins

Worker groups
Allows multiple servers to be grouped together to ease administration

Resource Manager 
(Enterprise Edition only.)
Provides the ability to monitor, report and collect server resource metrics for all servers in a farm.
Provides customizable metrics and reporting, real-time graphs and alerts, and capacity planning for server farm resources.

Load Manager
(Advanced and Enterprise Editions.) Provides load balancing of user connections across servers to more effectively use server resources  
Ensures that each user connects to the server most capable of handling the connection

Web Interface
Provides users access to published resources in one or more server farms through a web browser or the Citrix online plug-in.
The Web Interface provides user access to the published applications through a web browser. The web interface allows for multi-farm administration from a single Access Suite Console

Delivery Service Console
Allows administrators to configure administrative permissions and published resources


Citrix Plug-ins
Makes it possible for users to access published resources