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DPA alerts won't doesn't trigger on empty be pool / when metric is unavailable

Author: thisisanniefang

articles/load-balancer/load-balancer-standard-diagnostics.md

@@ -289,6 +289,9 @@ To configure alerts:
 
 ### Inbound availability alerting
 
+  >[!NOTE]
+  > If your load balancer's backend pools are empty, the data path availability metric will not be available because the load balancer is unable to find a valid data path to test. In this case, any configured Azure Alerts on the data path availability metric will not trigger.
+
 To alert for inbound availability,  you can create two separate alerts using the data path availability and health probe status metrics. Customers may have different scenarios that require specific alerting logic, but the below examples will be helpful for most configurations.
 
 Using data path availability, you can fire alerts whenever a specific load-balancing rule becomes unavailable. You can configure this alert by setting an alert condition for the data path availability and splitting by all current values and future values for both frontend port and frontend IP address. Setting the alert logic to be less than or equal to 0 will cause this alert to be fired whenever any load-balancing rule becomes unresponsive. Set the aggregation granularity and frequency of evaluation according to your desired evaluation.