I have created an Azure alert for a custom heartbeat metric - the heartbeat logs every minute, and if there are less than some count of heartbeats in a period it's supposed to fire.
However, I have found that in reality, when the service dies and stops creating heartbeats, the resulting count in the alert rules is "NULL". I can see a brief window of time where an alert condition is created while the service is dying and creating a few heartbeats, but once it's totally dead Azure is counting is as null.
I found this Microsoft documentation that seems to explain the reasoning and some of the behind the scenes logic.
But it still doesn't resolve my issue - how do I create an alert based on a metric if the metric falls down to zero? In NewRelic there were "signal loss" type alerts I could create - is there something similar for Azure? Thanks.