A simple way to trigger an alert when a metric value does not change over a set period of time is to start by using the diff() function on your query. This will produce the delta values from consecutive data points.
Next, apply the abs() function to take the absolute value of these deltas.
These functions can be applied to your query in the UI, via the "+" button.
Alternatively, your complex query can be manually entered in the 'edit monitor' UI, via the Source tab (or applied programmatically via the API). See image below.
For alert conditions in the metric monitor itself, configure as follows:
- Select threshold alert
- Set the "Trigger when the metric is..." dropdown selector to below or equal to
- Set the "Alert Threshold" field to 0 (zero)
This configuration will trigger an alert event when no change in value has been registered over the selected timeframe.
Other alert conditions/options can be set to preference. Your monitor's UI configuration should end up looking something like this: