add etw log for missing instrumentation key

[TimothyMothra]

#1260

If I telemetry item has made it all the way to the TelemetryChannel without an Ikey, it is safe to assume than an Ikey was never configured.
Here I want to emit a UserActionable ETW Error.

Note that ETW Event 56 is a config time warning, whereas ETW Event 57 is a channel time error.

[Dmitry-Matveev]

Still have some doubts on emitting NoIkey message always - maybe, only in Release mode? See comments.

[Dmitry-Matveev]

Just to keep in mind - some custom channel implementations maybe OK with no instrumentation key, such as custom file writer to save telemetry locally.

Also, AI VS Output / AI VS Integration UX may not need IKey to power up its experiences - will we emit this message for those scenarios? These scenarios might be fairly common, we can put #if !debug here to avoid this message in VS/Debug.

[TimothyMothra]

The #if !debug would be a compile time switch. I don't think we can detect when a consumer is in debug mode

[cijothomas]

Even if we do it, we should Log it once maybe, rather than for every item? Or maybe once in few seconds..

[TimothyMothra]

@Dmitry-Matveev, I don't know how to balance the concern that an empty ikey could be valid. I don't know enough about these scenarios.
Do you think it's valid to optimize for the most common/expected scenarios?

@cijothomas, I agree for every item is too much, but I'm reluctant to log only once because I don't want the log to get missed. I can ask Raj for a second opinion on how frequent he thinks the log should be to get recognized.

[Dmitry-Matveev]

Something like Debugger.IsAttached can be a better pick here - does not execute locally in VS, does execute when deployed to PROD. One notable issue - log won't be published if you debug in production, e.g. with WinDbg or remote debugging, but that should not matter already since you are capturing everything you need in debugger.

[TimothyMothra]

@Dmitry-Matveev's comment about channels got me thinking about what if we only set this on our 1st party channels.
And I just discovered the log I'm adding already exists on both!
However, both channels restrict this to Verbose logs only.
I'm not sure if our troubleshooting guides are collecting this. I will investigate...

ApplicationInsights-dotnet/BASE/src/Microsoft.ApplicationInsights/Channel/InMemoryChannel.cs

Lines 136 to 144 in 7633ae8

	if (string.IsNullOrEmpty(item.Context.InstrumentationKey))
	{
	if (CoreEventSource.IsVerboseEnabled)
	{
	CoreEventSource.Log.ItemRejectedNoInstrumentationKey(item.ToString());
	}
	return;
	}

ApplicationInsights-dotnet/BASE/src/ServerTelemetryChannel/ServerTelemetryChannel.cs

Lines 266 to 274 in 4ff3b7f

	if (string.IsNullOrEmpty(item.Context.InstrumentationKey))
	{
	if (TelemetryChannelEventSource.IsVerboseEnabled)
	{
	TelemetryChannelEventSource.Log.ItemRejectedNoInstrumentationKey(item.ToString());
	}
	return;
	}

[Dmitry-Matveev]

We may want to improve our existing throttling mechanism for diagnostic events to check whether it can be lock free as this one.

[TimothyMothra]

#1483