Add trace_flags.sampled context data entry to Log4j Core provider

[ppkarwasz]

Is your feature request related to a problem? Please describe.

Some structured log formats like the format accepted by FluentD stackdriver do not accept the W3C trace-flags field, but expect each flag to be stored separately.

Describe the solution you'd like

It would be useful to add an option to opentelemetry-log4j-context-data-2.17-autoconfigure to export each trace flag separately to the Log4j Core context data.

Since currently there is only one flag defined, the custom context data provider could export an entry with name trace_flags.sampled and boolean value.

Describe alternatives you've considered

Currently it is still rather easy to emulate the behavior of the trace_flags.sampled entry described above by replacing returning true if trace_flags is 01 and false if trace_flags is 00. This workaround, however, will no longer work if the W3C defines additional trace flags.

Additional context

No response

[ppkarwasz]

I can of course provide a PR if the proposed solution is accepted.

[trask]

this format is part of the specification: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/compatibility/logging_trace_context.md#overview

it might be better to add support for this in fluentd instead of adding this to all opentelemetry logging instrumentation across all languages

[ppkarwasz]

this format is part of the specification: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/compatibility/logging_trace_context.md#overview

Thanks for the explanation. In such a case I believe I can close this feature request.

@trask, to fully profit from the trace flags, it would be useful to have a custom Log4j Core filter to increase the logging verbosity, whenever sampled is set to true. Is this something you would be willing to accept in opentelemetry-log4j-context-data-2.17-autoconfigure?

[trask]

Is this something you would be willing to accept in opentelemetry-log4j-context-data-2.17-autoconfigure?

I'm not sure I fully understand the proposal, could you open a new issue and outline?

[ppkarwasz]

Done: #13804