AWS Resource detector fails with an error if metadata not available

[dackroyd]

If the instance metadata is not available, no resource and an unavailable EC2 client error will be returned

https://github.com/open-telemetry/opentelemetry-go-contrib/blob/7e7d779/detectors/aws/aws.go#L42-L45

client := ec2metadata.New(session)
if !client.Available() {
	return nil, errors.New("unavailable EC2 client")
}

This is counter to the documented behaviour for resources which should be:

Note the failure to detect any resource information MUST NOT be considered an error, whereas an error that occurs during an attempt to detect resource information SHOULD be considered an error.

https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/resource/sdk.md#detecting-resource-information-from-the-environment

A similar issue was raised (and fixed) with the ENV var detection in the main OTel library: open-telemetry/opentelemetry-go#1114 / open-telemetry/opentelemetry-go#1170

The GCP resource in this contrib library appears to implement detection correctly, returning no error:

https://github.com/open-telemetry/opentelemetry-go-contrib/blob/7e7d779/detectors/gcp/gce.go#L38-L40
https://github.com/open-telemetry/opentelemetry-go-contrib/blob/master/detectors/gcp/gce.go#L102-L104

if !metadata.OnGCE() {
	return nil, nil
}

if _, undefined := err.(metadata.NotDefinedError); undefined {
	return false
}

[MrAlias]

Instead of

if _, undefined := err.(metadata.NotDefinedError); undefined {
	return false
}

I would use the new errors package functionality:

if errors.Is(err, metadata.NotDefinedError)
	return false
}

Otherwise, this looks like a good fix. Thanks for opening it.

[dackroyd]

To clarify, the code snippets I included are the existing code for the aws and gcp detectors: none of that was suggested fix. The err.(metadata.NotDefinedError) is the current code in the gcp detector

[dackroyd]

As for a suggested fix, this might be appropriate:

client := ec2metadata.New(session)
if !client.Available() {
	return nil, nil
}

[MrAlias]

Ah, my mistake @dackroyd!

Would you be willing to put together a PR with this?

[dackroyd]

I'd be happy to push that change 👍

[MrAlias]

I'd be happy to push that change

Awesome, thanks for the help! 😄