Monitoring and Telemetry
ASP.NET health monitoring enables system administrators to monitor the status of deployed Web applications.
A number of tools are available to help you test and monitor the performance of your Web application. ASP.NET includes performance counters that you can use to track the execution of your application. You can also use the built-in ASP.NET tracing feature to track code execution for a page or an application.
E-book chapter that explains why a good monitoring system is necessary and provides information about what systems are available. It also covers logging best practices.
An introduction to Application Insights monitoring service of Microsoft Azure.
10-part video series about Application Insights.
MSDN documentation about using Application Insights to monitor web applications.