Rules

Rules

Rules are the metrics by which the hardware resources are measured or monitored . One rule, for example, reports the CPU utilization of a particular server. Rules make up a load evaluator. You can choose from the following 11 rules provided by Citrix MPS to create an evaluator that will meet your server farm's needs:

• Server User Load This rule balances load based on the number of users who log in to a particular server. It spreads load evenly between servers. You can specify any value between 1 and 10,000 to indicate that the server is at 100% capacity. So if you set the value to 100, when the number of users on this server reaches 100, new connections are denied .

• Application User Load This rule is fairly straightforward; it calculates load based on the number of users accessing a published application. You can specify any value between 1 and 10,000 to indicate that the server is at 100% capacity.

• CPU Utilization As the name implies, this rule calculates load based on CPU utilization. It allows you to set a low and a high threshold. When the CPU is within the low/high threshold you configured, load management reports a load. If the threshold reaches the high value that you set, it reports a 100% capacity reached on the server and denies new connections. If the CPU is below the low threshold you configured, no load is reported . The values that you can configure for this rule are between 1 and 100 and are in percentage of utilization. Figure 8.1 shows the CPU Utilization rule configured with a high threshold of 80 and a low threshold of 15.

  Figure 8.1. A load evaluator with the CPU Utilization rule added.

  

• Context Switches This rule calculates load based on the number of times a CPU context switch occurs. A context switch occurs every time the operating system switches from one executing process to the other. Similar to CPU Utilization, this rule enables you to configure a low/high rule whereby once context switching is within the configured threshold, load is reported. The valid configurable values are 02147483647.

• Disk Data I/O This rule calculates load in kilobytes based on disk data I/O. It has a low/high configurable threshold, and the same as the other rules, when the disk data I/O is within the low/high threshold, load is reported. The valid configurable values are 02147483647.

• Disk Operations This rule calculates load based on disk operations per second. It has a low/high configurable threshold, and the same as the other rules, when the Disk Operations are within the low/high threshold, load is reported. The valid configurable values are 02147483647.

• IP Range This rule is not really a load rule because it does not actually use any criteria to spread load. Instead, it is used to control access to published applications based on an IP range. For example, if a client's computer falls within this IP range, this rule allows or does not allow access. This rule should be used in conjunction with another rule to achieve some level of load management. Figure 8.2 shows the configurable values of the IP Range rule.

  Figure 8.2. The IP Range Rule value settings.

  

• Memory Usage This rule calculates load based on memory utilization. It allows you to set a low and a high threshold. When the memory is within the low/high threshold you configured, load management reports a load. If the threshold reaches the high value that you set, it reports a 100% capacity reached on the server and denies new connections. If the memory utilization is below the low threshold you configured, no load is reported. The values that you can configure for this rule are between 1 and 100. In Figure 8.3, Memory Usage is configured with a high threshold of 90 and a low threshold of 10.

  Figure 8.3. The Memory Usage Rule settings window.

  

• Page Fault This rule allows the load evaluator to calculate load based on the number of page faults per second that occur. A page fault occurs every time the operating system uses physical memory flushed to the hard disk. It has a low/high threshold configuration. The valid configurable values are 02147483647.

• Page Swap This rule allows the load evaluator to calculate load based on the number of page swaps per second that occur. A page swap occurs every time the operating system uses physical memory instead of virtual memory. It has a low/high threshold configuration. The valid configurable values are 02147483647.

• Scheduling This rule, similar to the IP Range rule, is not considered a load-balancing rule. It is used to allow or disallow access to a server or published application during specific days of the week or times of the day. This rule should be used in conjunction with another rule so that load management can really spread load. As you can see in Figure 8.4, you can set the time and date for the Scheduling rule.

  Figure 8.4. Configuring the Scheduling rule.

  

A Blast from the Past

Prior to MetaFrame Presentation Server 3.0, there was a 12th rule that you could add to a load evaluator. That rule, called the License Threshold, has been removed in MPS 3.0 because the licensing module has been removed and is now available in the Citrix License server.

The License Threshold rule allowed you to control or balance load based on the number of licenses that users consumed when accessing a particular application. Imagine you had three applications in your organization, each belonging to a different department. Department 1 did not want Department 3 to take advantage of its licenses and wanted to ensure that when its users logged in, a license would be available. With this rule, you could configure the licensing threshold for each published application with a certain number of available licenses. When that amount was reached, the load was reported as full, and no further connections were allowed. The valid range was between 0 and 9,999.

Now that you have learned the rules available, it's time to look at the categories or types that these rules fall within. These rules can belong to the following four categories:

• Moving Average This type or category hosts rules that are based on the percentage of the resource being used.

• Moving Average Compared To High Value This type hosts rules that use a percentage to calculate high and low thresholds based on the values 02147483647.

• Incremental This type hosts rules that use an integer value to determine when the server or published application has a full load. For example, if you set a value to 30, when you have 30 users on a server, no more connections can be allowed.

• Boolean This type hosts rules that simply allow or disallow connections.

Table 8.1 organizes the rules within their respective types.

Table 8.1. Rule Types

Type	Moving Average	Moving Average Compared to High Value	Incremental	Boolean
Rule	CPU Utilization	Context Switches	Server User Load	IP Range
	Memory Usage	Disk Data I/O	Application User Load	Scheduling
		Disk Operations
		Page Fault
		Page Swap

Alert

You should be aware that prior to MetaFrame Presentation Server 3.0, there existed a 12th rule by which load could be calculated; it was known as the License Threshold. Because licensing has been moved to a separate licensing server in MPS 3.0, this rule is no longer a configurable option and does not show up. Be aware of trick questions on the exam.