how to exclude exceptions from azure function's appinsight? - azure

Question

We have this host.json file in our azure function:
{
"version": "2.0",
"functions": [ "xxx" ],
"logging": {
"applicationInsights": {
"samplingExcludedTypes": "Request",
"samplingSettings": {
"isEnabled": true
}
}
}
}
Now we want to exclude exception to be automatically logged as well (as we handle exceptions ourselves in try catch block, so don't want it logged twice).
However, I am not sure samplingExcludedTypes is the right property to use, according to this issue:
https://github.com/MicrosoftDocs/azure-docs/issues/47219, excludeTypes is the one to use
Should I just do this:
"logging": {
"applicationInsights": {
"samplingSettings": {
"isEnabled": true,
"excludedTypes": "Request;Exception"
}
}
}

Answer 1

Normally I would say that what you need is a Telemetry Processor or Telemetry Initializer, depending on the language, that drops all exception telemetry. But unfortunately that does not work in an Azure Function, it is not supported.
We can, however, leverage the sampling settings to prevent telemetry from being send by forcing it to be sampled out. It does work when adaptive sampling is enabled (I just didn't try for other types of sampling) which is the default sampling behavior of an Azure Function. To do that we can set the ProactiveSamplingDecision property like this:
public class DropExceptionTelemetry : ITelemetryInitializer
{
public void Initialize(ITelemetry telemetry)
{
if (!(telemetry is ExceptionTelemetry item)) return;
item.ProactiveSamplingDecision = SamplingDecision.SampledOut;
}
}
Also, don't forget to add this initializer using DI:
public class Startup : FunctionsStartup
{
public override void Configure(IFunctionsHostBuilder builder)
{
builder.Services.AddSingleton<ITelemetryInitializer, DropExceptionTelemetry>();
builder.Services.AddLogging();
}
}
For this to work, make sure Exception is not listened in the exludedTypes property
"applicationInsights": {
"samplingSettings": {
"excludedTypes": "Event;Request"
}
}