Azure application insights - exclude custom event from sampling

Question

I have a .NET Core web app which is sending some custom events telemetry to Application Insights. The custom events are sent using telemetry client instace, e.g. like that:

  telemetryClient.TrackEvent(Names.FileDownload, new Dictionary<string, string>()
            {
                {PropertyKeys.ProjectName, project.ProjectName},
                {PropertyKeys.ProjectUri, project.ProjectUri},
                {PropertyKeys.IsLocal, isLocal.ToString() },
                {PropertyKeys.FileSize, fileSize?.ToString() },
            });

Most of the data events that occur are in massive numbers and I don't care about all of them, so I have set up sampling to 50%.

However, I have one or two events that occur very infrequently, and for those I want each occurrence to be tracked.

With sampling enabled, I see that this crucial event is almost never stored. When I disable the sampling, it starts to work.

Is it possible to somehow exclude certain telemetry items from being filtered by sampling?

Regards,
Bartosz

what's kind of the web app? .net core or .net framework or others? — Ivan Yang

Ivan Yang Ivan Yang · Accepted Answer · 2020-05-05T01:38:49

Yes, it is possible. You can write a custom TelemetryInitializer, which sets the SamplingPercentage to 100 on the telemetry item you want retained.

Here is the sample code:

public class MyTelemetryInitializer : ITelemetryInitializer
{
    public void Initialize(ITelemetry telemetry)
    {
        #write your own logic for somecondition
        if(somecondition)
        {
            ((ISupportSampling)telemetry).SamplingPercentage = 100;
        }
    }
}

For more details, please refer to this article, in section "There are certain rare events I always want to see. How can I get them past the sampling module?".

Azure application insights - exclude custom event from sampling

1 Answers