programmatically set the Instrumentation Key
var instrumentationKey = ConfigurationManager.AppSettings["ApplicationInsightsInstrumentationKey"];
if (string.IsNullOrWhiteSpace(instrumentationKey))
{
throw new ConfigurationErrorsException("Missing app setting 'ApplicationInsightsInstrumentationKey' used for Application Insights");
}
TelemetryConfiguration.Active.InstrumentationKey = instrumentationKey;
new TelemetryClient().TrackEvent("Application started");