read tracing info from system properties

[jdoherty]

Opened to address the following feature request:

#7579

[mateuszrzeszutek]

Also pinging @open-telemetry/lambda-extension-approvers

Should we also update the spec while we're at it? Quoting @tylerbenson's comment from #7579 :

I think the main question I have is can this be included in the relevant spec somehow? When I updated that section earlier this year, I didn't understand or expect that the environment variable was updated for each request as that's not something normal applications do. I think it's worth adding or linking to some documentation about this environment variable's purpose and odd behavior. I haven't found any docs on it.

[jdoherty]

@tylerbenson @laurit could you take a look at this please? Alexander has approved this but is not a repo owner. Any thoughts are appreciated. cheers

[trask]

thx!

do you know if there is any official docs on this system property from AWS?

the order of precedency (env var vs system prop) looks different from:

https://github.com/aws/aws-xray-sdk-java/blob/711e48cfd54400e728f99bec3bb3baf417276b46/aws-xray-recorder-sdk-core/src/main/java/com/amazonaws/xray/contexts/LambdaSegmentContext.java#L43-L46

also, do you know why aws/aws-xray-sdk-java#251 is not resolved?

[tylerbenson]

(I would also love to see better documentation about this system property and corresponding environment variable linked somewhere, including the quirky lifecycle of the environment variable that led to this PR.)

[smirnoal]

I will chase both the SDK issue closure and updating the public docs

[jdoherty]

@trask @tylerbenson now we seem to have broad agreement on the docs over on open-telemetry/semantic-conventions#27 can we approve this one?

[smirnoal]

I will chase both the SDK issue closure and updating the public docs

both achieved, docs were updated: https://docs.aws.amazon.com/lambda/latest/dg/configuration-envvars.html#configuration-envvars-runtime

[tylerbenson]

@smirnoal Thanks for the update. I'd like to suggest adding a bit more to the xray tracing header section... specifically I think you should note that this doesn't behave like a normal environment variable because it changes for each function invocation. When I first encountered this it was surprising to me and some systems don't expect that. I assume Java is one example that doesn't handle dynamic environment variables well which is why you needed the system property to take priority.