Specifications

Chapter 4: Configuring the High-Level Network
4-12
The metric coefficient is a factor determining how heavily the metric’s value
counts in the overall ratio weight calculation. The metric threshold is the
highest value allowed for the metric if the metric is to have any weight at all.
To understand how to use these values, it is necessary to understand how the
overall ratio weight is calculated. The overall ratio weight is the sum of
relative weights calculated for each metric. The relative weights, in turn, are
based on three factors:
• the value for the metric returned by the monitor
• the coefficient value
• the threshold value
Given these values, the relative weight is calculated as follows:
w=((threshold-value)/threshold)*coefficient
You can see that the higher the coefficient, the greater the relative weight
calculated for the metric. Similarly, the higher the threshold, the greater the
relative weight calculated for any metric value that is less than the threshold.
(When the value reaches the threshold, the weight goes to zero.)
Note that the default coefficient and default threshold values shown in
Table 4.3 are metric defaults, not template defaults. The template defaults
take precedence over the metric defaults, just as user-specified values in the
custom real_server monitor take precedence over the template defaults. For
example, in Figure 4.2, the template specifies a coefficient value of 1.5 for
ServerBandwidth and no value for the other metrics. This means that the
template will use the template default of 1.5 for the ServerBandwidth
coefficient and the metric default of 1 for the coefficients of all other
metrics. However, if a custom monitor my_real_server were configured
specifying 2.0 as the ServerBandwidth coefficient, this user-specified
value would override the template default.
The syntax for specifying non-default coefficient or threshold values is:
<metric>:<coefficient |<*>:<threshold>
The following examples show how to specify a coefficient value only, a
threshold value only, and a coefficient and a threshold value, respectively.
b monitor my_real_server ’{ use real_server metrics CPUPercentUsage:1.5 }’
b monitor my_real_server ’{ use real_server metrics CPUPercentUsage:*:70 }’
b monitor my_real_server ’{ use real_server metrics CPUPercentUsage:1.5:70 }’
Metric coefficient and threshold are the only non-template defaults. If a
metric not in the template is to be added to the custom monitor, it must be
added to the metric list:
b monitor my_real_server ’{ use real_server metrics "HTTPClientCount" }’
To associate the monitor with the member node
Associate the custom health check monitor with the server node, creating an
instance of the monitor for that node:
b node <node_addr> monitor use my_real_server