Load Evaluators and Rules

Load Evaluators and Rules

Citrix MetaFrame was built with enterprise scalability in mind. In any IT shop, you will notice that not all servers have the same hardware. This is obviously due to the different times at which servers were purchased, and with the constant advances in the IT world, you are almost certain to get a different CPU clock speed and newer , better components in every server you purchase.

When you add newer, better servers to your farm, you expect these servers to handle more load than existing servers with older hardware. Now imagine if you were doing just standard load balancing, which means spreading user load across all available servers equally. In this case, you do not really benefit from the new hardware you purchased because all the servers get an equal amount of load.

Citrix load management was designed with this fact in mind, and that is why it allows you to customize how load is spread based on load evaluators and rules. A load evaluator is a grouping of several rules that can be applied to servers to provide load balancing. Load evaluators consist of one or more rules. Rules are configurable agents that measure or monitor specific resources on the servers. Two load evaluators are available with MetaFrame Presentation Server Advanced and Enterprise Editions: the Default load evaluator and the Advanced load evaluator. The following sections closely examine each of these two components.

Default

The Default load evaluator is assigned to all servers by default. This evaluator's function is reasonably simple: It balances the load based on the user load rule. You can also set a maximum user limit. For example, if you set the limit to 150 users, when the 151 ^st user tries to establish a session, that user is rejected by the server. This evaluator cannot be modified or deleted. Using this load evaluator is probably a good idea if you are dealing with servers that have the same hardware configurations. When you start mixing and matching servers with different hardware, however, this evaluator does not meet the challenge.

Advanced

The advanced load evaluator is much more powerful than the default and is better suited to handle servers with different hardware resources. It balances the load based on the CPU utilization, memory usage, and page swaps rules.

Note

Both the default and advanced load evaluators are preconfigured and cannot be changed or altered . You should consider creating your own load evaluator based on the set of rules that best suit your environment to achieve the best performance and optimization possible.

It's important to note that load evaluators can be assigned to either servers or published applications. It's also important to know that only one load evaluator can be assigned to a server or published application. In the event that a published application has a load evaluator and also is hosted on a server that has a load evaluator assigned to it, the evaluator with the highest threshold is used.

Alert

Default and Advanced evaluators cannot be directly modified, but they can be copied and used to create new rules if desired.