ParentContextExtractor should read tracing info from system property

[smirnoal]

Is your feature request related to a problem? Please describe.
Java does not have a good mechanism for modifying environment variables. There are some hacky solutions which use Reflection API, and modify the UnmodifiableMap which holds the variables. This technique is now discouraged by Oracle. Good reads on this topic: blog post by Oracle

Because of this, setting tracing information via _X_AMZN_TRACE_ID is challenging in new versions of Java, even with the hack.

Would it be possible to implement reading tracing information from a system property, not from an environment variable? aws-x-ray-sdk-java implemented this some time ago: link

Describe the solution you'd like
Optionally read tracing information from com.amazonaws.xray.traceHeader system property.
Similarly to this PR: https://github.com/aws/aws-xray-sdk-java/pull/252/files

Additional context
Perhaps, this class should be modified: link

[trask]

Would it be possible to implement reading tracing information from a system property, not from an environment variable? aws-x-ray-sdk-java implemented this some time ago: link

it looks like that issue is still open?

[smirnoal]

and still actual. Would be great if someone can pick it up. Looks pretty straightforward to implement

[trask]

copying folks who may have knowledge/thoughts/interest: @willarmiros @tylerbenson @open-telemetry/lambda-extension-approvers

[tylerbenson]

Note that in #7970, the span context in this env var becomes a span link instead of the parent. I have no objection to reading from both locations for populating the span link.

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.

@smirnoal is this something you (or someone else at AWS) would be interested in working on?

[smirnoal]

I believe with the PRs merged, this issue can be closed. Would be good to know which release will contain the fix

[mateuszrzeszutek]

That will be release 1.27.0, which should happen in ~2 weeks.

[smirnoal]

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