With application diagnostics, you can capture information that is produced by the app itself. To capture this information, the developer uses the System.Diagnostics.Trace class in the application code to log the information to the application diagnostics log. You can retrieve these logs at runtime for troubleshooting. 

When you publish the application to App Service, deployment information is automatically logged with diagnostic logging without needing to be configured. This can give you information about why a deployment failed. 

In the next section, we are going to enable diagnostic logging in the Azure portal.