Health windows

A health window is a trailing time frame in which the ServiceNow system evaluates audit results from CIs that have desired state fields defined.

Each window is defined by the Health window and Health unit fields, and ends when an audit runs. For example, an audit that runs on the 15th of the month with a 7 day window, evaluates a desired state field's threshold values from the 8th to the 15th. When the same audit runs the next day, the system evaluates the threshold from the 9th to the 16th, and so on, counting backward 7 days from the current day. ServiceNow evaluates a CI's threshold values for each health window, without considering the results from the previous window. As a result, a CI's health can fail for one audit and then pass in a subsequent audit that runs in a new window.

ServiceNow evaluates stability by recording the number of times a CI's desired state threshold value switches between Failed and Certified within the health window. In the example shown here, a 5 minute health window was set for the desired state field on a UPS unit that measures the remaining battery time. The threshold was set at 2, which allows the field to fail two audits in the same health window.
Figure 1. Desired State Health Window
In the initial audit, the system evaluated the threshold value for the Seconds on battery field within a 5 minute window running from 13:52:51 to the time of the audit at 13:57:51. The desired state field showed In Limit for that audit and the second audit conducted less than a minute later. The next two audits were conducted within 5 minutes of the first audit and both showed that the threshold (set at 2) was Exceeded. A subsequent audit was conducted 5 minutes after the audit in which the desired state field threshold was first exceeded. Since the health window had moved forward enough units, the Seconds on battery field was within limits again with only one failure in the 5 minute window being evaluated.
Figure 2. Desired State Health Results