So, again, I’m trying to tame Application Insights. My logs are filling up with various requests for different health-check URLs. These get requested, over and over, day after day, and all are recorded in App Insights as Requests. However, I don’t care about these requests if they’re successful. In fact, I only care about if they fail. Can I exclude them?

Yes, I can. I’ll build a telemetry processor to filter them out.

public class RequestFilter : ITelemetryProcessor
{
	public string UrlContains { get; set; }
	public string ResponseCode { get; set; }
	public string FilterIfAllMatch { get; set; }
	
	private ITelemetryProcessor Next { get; set; }

	// next will point to the next TelemetryProcessor in the chain.
	public RequestFilter(ITelemetryProcessor next)
	{
		FilterIfAllMatch = "true";  //Default to all must match
		this.Next = next;
	}

	public void Process(ITelemetry item)
	{
		RequestTelemetry requestTelemetry = item as RequestTelemetry;
		if (requestTelemetry != null )
		{
			int rule = 0;
			int pass = 0;

			if (!string.IsNullOrEmpty(UrlContains))
			{
				rule++;
				if (!requestTelemetry.Url.ToString().Contains(UrlContains))
				{
					pass++;
				}
			}

			if (!string.IsNullOrEmpty(ResponseCode))
			{
				rule++;
				if (!requestTelemetry.ResponseCode.Equals(ResponseCode, System.StringComparison.OrdinalIgnoreCase))
				{
					pass++;
				}
			}

			if (FilterIfAllMatch == null || FilterIfAllMatch.Equals("true", System.StringComparison.OrdinalIgnoreCase))
			{
				// If all rules match, then there are no passes.
				if (pass == 0 && rule > 0) return;
			}
			else
			{
				// Else if any rules match, then there are no passes
				if (pass < rule) return;
			}

		}

		this.Next.Process(item);
	}

	public override string ToString()
	{
		return string.Format("RequestFilter: {0} , {1}, {2}", UrlContains, ResponseCode, FilterIfAllMatch);
	}
}

This filter checks a number of rules, and can filter messages that match one or more, or that match ALL the rules. The rules check status code, or does the URL contain a particular string. Note the public properties in the class – this allows configuration to be set in the ApplicationInsights.config file:

Note also that you can add multiple of these TelemetryProcessors, so you could exclude other requests and response codes in addition.