Difficulty using Resource::from_detectors to set service.name correctly

[BrynCooke]

SdkProvidedResource detector currently has to know about all other detectors to correctly set service.name.

Detectors currently fill out resources in a last one wins fashion. In the following situation EnvResourceDetector, upon finding service.name will overwrite the value even if the SdkProvidedResourceDetector obtained it from OTEL_SERVICE_NAME.

let resource = Resource::from_detectors(
            time::Duration::from_secs(5),
            vec![
                Box::new(SdkProvidedResourceDetector),
                Box::new(EnvResourceDetector::new()),
            ],
        );

It's possible to reverse to ordering of the resource detectors to get the right result, but this doesn't support adding other resource detectors.

let resource = Resource::from_detectors(
            time::Duration::from_secs(5),
            vec![
                Box::new(MyResourceDetector::new()),
                Box::new(EnvResourceDetector::new()),
                Box::new(SdkProvidedResourceDetector),
            ],
        );

In this case SdkProvidedResourceDetector will override any value obtained by MyResourceDetector with unknown_service if it can't find anything from env.

Relates to #1295

[BrynCooke]

The issue seems to be that if a detector does defaulting then it leads to issues. The following works:

 let resource = Resource::from_detectors(
            time::Duration::from_secs(5),
            vec![
                Box::new(MyResourceDetector::new()),
                Box::new(EnvResourceDetector::new()),
                Box::new(EnvServiceNameDetector::new()), //Only sets service.name if it exists in env.
            ],
        );
        

Proposal: If instead Resouce itself is responsible for defaulting service name then it can take a look at the attributes after all detectors have been resolved and see if service name is missing.

[flokli]

I'm interested in this as well. I initially made an attempt extending SdkProvidedResourceDetector with a fallback_service_name: Option<String> (deriving Default) and adding a constructor for the fallback name, but it requires everyone to "properly" create an instance (you can't just use SdkProvidedResourceDetector.detect anymore).

I think your approach of letting Resource take care of defaulting a service name if unset is nicer, and I favor it.

[cijothomas]

@pitoniak32 Is this something you can help triage, as you already helping in this area?