An Azure web app named webapp1 running on .NET Core sends telemetry to an Application Insights resource named AppInsights1. You must enforce a fixed sampling rate for telemetry from webapp1. Which file should you modify in the webapp1 codebase?

For .NET Core applications, Application Insights telemetry configuration, including sampling rates, is typically managed programmatically within the application's startup code. The Startup.cs file is where services are configured and the application's request pipeline is defined, making it the appropriate place to set up and customize Application Insights telemetry, including fixed sampling. Modifying ApplicationInsights.config is primarily for older .NET Framework applications. Usage and estimated costs settings in AppInsights1 are for monitoring billing, not configuring telemetry behavior. Continuous export settings in AppInsights1 are for exporting collected telemetry data, not for defining how data is sampled at the source.