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Basic Principles of designing Citrix XenApp Environments Part 2

This article is part two of an article series about Citrix XenApp design decisions. The starting article can be found here.



Zones Architecture & Design

Zones within Citrix infrastructures are logical segments within a Citrix farm. Every zone has a data collector (described in the next paragraph). Servers in a zone will communicate with his zone data collector where the data collectors of every zone will exchange information which each other about his zones.

When determine the needs for zones and the amount of zones used the following considerations:

  • Available bandwidth

When there is limited bandwidth available the traffic between the servers within one zone can be too much for the network link. If this is the case it is a good idea to create zones to regulate the traffic of the Citrix infrastructure.

  • Amount of changes in the Farm

Every change made in the farm is logically distributed to the Citrix server to reflect the changed settings. How more changes are made logically more traffic is generated between the Citrix servers. Together with the available bandwidth the amount of changes can be a reason to divide the farm into zones.

  • Citrix advices a maximum of 25 zones

There is a limitation on the amount of zones. Citrix advises not to create more than 25 zones.

  • Citrix Policy "Zone Preferences"

Within the enterprise edition there is a policy available that makes it possible to route users automatically to another (set of) server(s) if the Published Application is not available on the first group. This policy based on zones, so if you would like to use this policy zones are necessary.

  • Load Sharing between servers

When using zones load sharing between servers can be arranged in two ways. There is a possibility to share the load over all servers despite if there are zones configured or the load is shared between servers in de zone only.  Using the first method the session of the user can be started on any server, while using the second methodology the users will be redirected to the server in the zone of the data collector, which handled his request.

  • Each zone needs to have a Data Collector

Remember that each zone needs a data collector. Although every server can facilitate the role of data collector logically this role requires some resources available to carry out the tasks. Keep this in mind when determine the amount of servers to host the applications and check the considerations in the next paragraph about the data collector.

Best practices concerning the zones are using as less zone as possible, use zones only when low bandwidth connections are available between servers and/or if the zone preferences policy is necessary for your environment (for example when using a back-up/disaster site).

Data Collector Architecture & Design

The data collector is a role on a Citrix XenApp server which is collecting, maintaining and managing dynamic information about the farm and zone. The data collector also passes the user to the least busy server. Every Citrix XenApp server can be facilitating the server role, but of course some resources are needed for this role.

When creating the design the following topics should be considered.

  • Dedicated Data Collector versus Non Dedicated Data Collector

Dependent on the size of the Citrix infrastructure (based on the amount of server, amount of users and logon/logoff activities) a decision should be made to use a dedicated server or a non dedicated server. A dedicated data collector is a server with Citrix XenApp installed, but the server is not hosting any Published Applications or Desktops. When using a Non Dedicated Data Collector think of using a different Load Evaluator with lower values. Also do not remember that data collector role should be assigned within the farm settings.

  • Back-up Data Collector

When the primary data collector fails or is unavailable the Citrix farm will organize an election to select a new data collector. The election is primary based on settings about the data collector role, but also on the version of the software and (some) hot fixes. Again dependent the back-up data collector can be dedicated server or a shared server.

  • Amount of Zones

As mentioned earlier in the zones part every zone has a data collector. When you have lots of zones you probably will choose for a non dedicated data collector in comparison with situations when there is/are just one or two zones.

Base on practical experiences I normally decide to use a dedicated primary data collector when there are more than 10 servers in the farm or zone. When there are more than 15 servers I also use a dedicated back-up data collector. In a case a farm/zone has less servers as mentioned I always use a specific load evaluator for server which are also hosting the data collector role (both primary as back-up). This role has rules with a lower value than the load evaluator I use for servers, which are only hosting applications.

To be continued

This article will continue in a next article describing more Citrix XenApp design decisions.