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XenApp and XenDesktop share a unified architecture called FlexCast Management Architecture (FMA). FMA’s key features are the ability to run multiple versions of XenApp or XenDesktop from a single Site and integrated provisioning.

FMA key components

A typical XenApp or XenDesktop environment consists of a few key technology components, which interact when users connect to applications and desktops, and log data about Site activity.

  • Broker Service – a Delivery Controller service that tracks which users are logged in and where, what session resources the users have, and if users need to reconnect to existing applications. The Broker Service executes PowerShell and communicates with the Broker agent over TCP port 80. It does not have the option to use TCP port 443.
  • Broker agent – an agent that hosts multiple plugins and collects real-time data. The Broker agent is located on the VDA and is connected to the Controller by TCP port 80. It does not have the option to use TCP port 443.
  • Delivery Controller – the central management component of a XenApp or XenDesktop Site that consists of services that manage resources, applications, and desktops; and optimize and balance the loads of user connections.
  • Virtual Delivery Agent (VDA) – an agent that is installed on machines running Windows Server or Windows desktop operating systems that allows these machines and the resources they host to be made available to users. The VDA-installed machines running Windows Server OS allow the machine to host multiple connections for multiple users and are connected to users on
    one of the following ports:
    TCP port 80 or port 443 if SSL is enabled
    TCP port 2598, if Citrix Gateway Protocol (CGP) is enabled, which enables session reliability
    TCP port 1494 if CGP is disabled or if the user is connecting with a legacy client
  • Citrix Receiver – a software client that is installed on the user device, supplies the connection to the virtual machine via TCP port 80 or 443, and communicates with StoreFront using the StoreFront Service API.
  • StoreFront – the interface that authenticates users, manages applications and desktops, and hosts the application store. StoreFront communicates with the Delivery Controller using XML.
  • Monitor Service – a Delivery Controller component that collects historical data and puts it in the Site database by default. The Monitor Service communicates on TCP port 80 or 443.
  • ICA File/Stack – bundled user information that is required to connect to the VDA.
  • Site Database – a Microsoft SQL database that stores data for the Delivery Controller, such as site policies, machine catalogs, and delivery groups.
  • NetScaler Gateway – a data-access solution that provides secure access inside or outside the LAN’s firewall with additional credentials.
  • Director – a web-based tool that allows administers access to real-time data from the Broker agent, historical data from the Site database, and HDX data from NetScaler for troubleshooting and support. Director communicates with the Controller on TCP port 80 or 443.
  • Studio – a management console that allows administers to configure and manage Sites, and gives access to real-time data from the Broker agent. Studio communicates with the Controller on TCP port 80.

The most comprehensive description of Citrix FMA you can find on Bas van Kaam blog: The Citrix XenApp & XenDesktop FMA Services complete overview