Citrix Xenapp

Citrix Xenapp: Xenapp is application virtualization software introduced by Citrix System, with help of Xenapp user can access any type of application from any device at any time and any where. We can assume Xenapp as a software bundle to virtualize application. Citrix delivers the virtualize application by various means such as hosted or streamed application delivery.
Xenapp line of product was launched by Citrix after acquisition of Xen group and earlier same product come with the names like Citrix Presentation server, Citrix metaframe server and Citrix Winframe. After the Xen acquization Citrix launched Xenapp 5.0, 6.0 and Xenapp 6.5. Latest product from this group is is Xenapp 7.5. With Xenapp user are able to access any application without even thinking about the installation process, up gradation process application management and local resource consumption such as CPU utilization, storage and other related issues. Even they can access the same application on some old PC that have less configuration as per the software industry standards. For example you have an old desktop with just 512MB of RAM installed and you are trying to access an application for which minimum RAM requirement is 1024MB. With Citrix you can access this application very easily as in this scenario application execution is taking place at server level. With Citrix all the application execution related process occurs at server level and users are accessing application in the in the same way as they used to access on their tradition desktop. Even application delivery process is so smooth that user get better experience in comparison to accessing the application on their own desktop in traditional way. To access applications user have to just download the necessary Citrix plugin and install it once, once done they are ready to access application without any limitation.
Xenapp Versions: To have better understanding about Xenapp we should know how many versions are available for user to use it. Currently Citrix offers Xenapp in three versions and they are as follow

1. Advance Edition: Advance version of Xenapp is basically for small network and can be used for understanding and troubleshooting purpose. It comes with features like any device/anywhere, enhanced user experience and central management console.
2. Enterprise Edition: Features offered in enterprise version include the entire advance version feature + VM hosted application, monitoring and recovery, profile management.
3. Platinum Edition: Platinum edition comprise of the entire advance version feature plus other features like single sing on, edgesight for monitoring, provisioning services and profile management.

Component Making Citrix Xenapp: To deliver virtualize application there is a long process running at the back hand of users device and user are even not aware of that and frankly speaking why should be they aware of that? As it is none of their business but for technical guys they should have clear understanding of component as well as the delivery process. So now let’s take a look at different component of Xenapp.

1. Farm: Citrix farm is collection of xenapp servers. Servers in farm communicate via IMA protocol and they are managed by data store.
2. Zone: Zone can be considered as the logical re-arrangement of Citrix farm or the servers present in farm. Creation of zone depends on certain factors such as geographical location. All servers in zone communicate with a common data collector.
3. Worker Group: Worker Group is basically a concept of dividing xenapp servers into smaller group for better management process. With the help of worker group it becomes easy to apply policies and other rules on servers. Suppose you have to upgrade certain servers out of a xenapp farm so in this case all you have to do is to create a worker group, add those servers in group and then apply updates. Servers would be updated without disturbing the configuration of rest of server.
4. Data Store: A data store is a server in Citrix farm responsible for maintaining static information. For example number of server in farm and policies applied to them, load balancing rule, application published in farm, printer configuration, license server name and port and security configuration. Each farm has a single data store irrespective of number of zones. Data store is basically a database server from which all the other member servers are connected. A data store can be configured on Microsoft SQL server, Oracle, IBM DB2 and MS Access.
5. Data Collector: A data collector is Citrix farm is responsible for maintaining dynamic information. For example no active and inactive session running in farm, load balancing information of each server in farm, server status like if it is online or offline, total license used by user . For each zone in farm there is one data collector. By default first server added in farm works as data collector. Also data collector communicates with other data collector present in farm for smooth application functioning.
6. Web Interface: We have application installed on server and they are ready to get delivered but how end user would access published application? Answer for this question is Web Interface. It allows user to access application via a standard web browser. Also to access application via web interface users are required a Citrix online plugin web. You can check out for different Citrix plugins in next articles.
7. License Server: License server is necessary in farm to determine the number of license available to the number of license currently in use. A license server keeps a track of all licensing related processing and releases license for user as per the requirement. Licensing can be per user or per device as configured. In xenapp farm we should have a Remoter Desktop Service License Server as well as Citrix License server for smooth licensing process. License server may or may not be a xenapp server.
8. Domain controller: As we all know that a domain controller is required for all the authentication related process, checking and validating then type of permission available to user and what type of application he can access.
9. Citrix XML Broker: As its name suggests it acts as a mediator between the different delivery processes. It acts as an intermediate between the other servers/data collector in farm and the web interface, passes user credentials from web interface and on successful identification of available server passes its information back to web interface. XML broker is a part of Citrix XML service which is installed on each and every server while xenapp installation. But XML broker is used only when XML service is acting as a communication bridge between different components of farm. By default the Citrix XML service uses port 80 but it is highly recommended by Citrix to use port 8080 for XML communication.
10. Citrix IMA: Citrix IMA (Independent Management Architecture) can be considered as both a service and a communication protocol as it has information of database as well as it is used for server to server communication. It helps in configuring, monitoring, and operating all XenApp functions as it has information of all xenapp configurations. Uses port 2512 for server to server communication and port 2513 for server to management console communication.
11. Citrix ICA: Citrix ICA (Independent Computing Architecture) is a connectivity protocol used for client to server communication unlike IMA where it is server to server communication. It is similar to Microsoft RDS and VMware PCoIP but it consumes very less bandwidth as it passes only mouse clicks and key strokes and is latency sensitive.

Application Delivery process: Now we are almost familiar with different component of Citrix farm, let have a look at application delivery process. We can break application delivery process into two parts one is related to user authentication process and determining which application user can access and second how the user access the application once he clicks on the required application.
Part One:

• Initially user enters his login credentials like username, password and domain to web interface to login.
• As soon as web interface receives credentials it passes the information to XML broker/data collector in farm.
• The XML server forwards this information to Domain Controller to check if the user has enough rights to access the application or not.
• Once it gets authentication approval from Domain Controller then XML server communicates with zone data store to gather information about the list of application on which user has access.
• Once information is retrieved from data store it passes back the information to web interface.
• Finally web interface displays all the available application on user desktop.

Part Two

• Now user can see all the application available to him, he tries to access any application.
• Information of application selected by user is passed to web interface and then to the zone data collector.
• Data collector determines the least busy server in farm and once it has identified it, checks whether the required application is installed on server or not. If the application is installed then it passes this information to web interface and with the server information resolved in terms of IP and if no then it searches for another server.
• Web interface now by using this IP information creates ICA file and transfers it to client device.
• Now user creates connection to least loaded server in farm and starts using application.
• Server on which user has created his connection now communicates with the license server of farm to check for required license.
• Once licensing process is complete user is all set to enjoy the Citrix application.