Netreo Essentials has a sophisticated alert engine that allows for very precise alerts to be published for very particular conditions. Netreo Essentials alerts are configured, maintained and raised at a resource level. The core component of an alert is its Expression, that governs when an alert is turned ON or OFF. Learn more about expressions here. An Alert's expression evaluates the metric values that are captured by Netreo Essentials. Learn more about metrics here.
Alerts are defined on the Alerts tab of a particular resource. During initial setup of a resource it is likely that a default configuration template was used, so when editing a particular resource it is likely that some alerts have already been predefined.
When creating new alerts, or changing existing ones, some configuration settings need to be provided for Netreo Essentials to effectively evaluate and raise alerts.
|Name||An Alert's name is important. It is what is used to identify an alert when communicating raised/cleared alerts to users or integration endpoints.|
|Enabled||Alerts can be disabled when they are no longer needed, but when their configuration details are still important to preserve for future use.|
|Severity||Severities identify the importance of a particular alert, serve as visual indicators of alerts on the dashboard, and are communicated via notifications to user or integration endpoints.|
|Evaluate by Instance||This setting applies and is visible only on resources that are "multi-instance" (i.e., resources that aggregate under them a number of ubiquitous instances, such as Azure Cloud Roles). When set to true, Netreo Essentials will evaluate metric-based conditions on a per-instance level. When set to false, Netreo Essentials will average metrics across all instances before evaluating them. For some alerts, it is important to know when a particular instance within a resource misbehaves, while for others it is important to know when all instances across the resources are impacted. (For example, checking for a low memory condition on Cloud Role instances is usually important to do by instance, so that one can know which instance is running low. However, checking for Web Requests/sec should likely be done across all instances to determine overall load on the website.)|
|Expression||Expressions are the core component of alerts. They determine the condition when an alert is raised and cleared. Expressions are boolean statements with C#-like syntax that need to evaluate to either TRUE or FALSE. More information about expressions can be found here.|
|Sustained Period||Expressed in minutes, sustained period is the period of time that Netreo Essentials will wait before raising an alert and assuming that the alert's condition continues to remain true. Sustained period ensures that alerts do not trigger erroneously for highly chaotic/frequently changing metrics/conditions. By configuring sustained period, Netreo Essentials will evaluate the expression during every monitoring cycle and ensure that it continues to remain true before finally raising the alert.|
Raising and Clearing Alerts
As mentioned above, alerts are raised when the expression of an alert evaluates to TRUE for a specified sustained period of time. An Alert is cleared when the expression evaluates to FALSE. An Alert's value is not changed if the alert's expression evaluates to any other value or to an error. When an alert is raised, it is tracked under the Active Alerts dropdown on the portal. Furthermore, when an alert is either raised or cleared, it is published to various people and integration API endpoints as governed by the Notification Management Screen. Learn more about notification management here.
All enabled alerts for a resource are evaluated during every monitoring cycle. The evaluation logic does not stop evaluating alerts after an alert is found to be TRUE.