Application Insights is an extensible application performance management (APM) service for web developers on multiple platforms. Customers use Application Insights to monitor live web applications, detect performance anomalies, diagnose issues and to understand usage patterns.
In addition to the alerts on application health based on different metrics, you can now monitor e-log files by setting up a query to run at specified intervals and trigger alerts based on the result. For example, let’s say you deployed a new fix for a specific exception and want to make sure it doesn’t surface again. You can now setup an alert to trigger if that exception appears in your Application Insights trace file.
Read about it in the Azure blog.