[DRAFT] #2529 Fix empty log sended if no raw body

[gillg]

Description:
Final plan to discuss (still in WIP for this reason).
For now this PR is working as expected, all logs sended from OTEL collector to Loki will be encapsulated in a JSON containing all OTEL attributes at its root level.
If you have a OTEL log body it wil be appened to the entry _otel_raw_log, and same thing for OTEL Name and OTEL Severity (in _otel_shortname and _otel_severity).

JSON Format is ok ?
Idea to have all attributes as top level is ok ?

Link to tracking Issue: #2529

Testing: Tested localy with a fluentbit windows exporter > OTEL fluentforward > OTEL Loki exporter > Loki

Documentation: Potential log format breaking change on Loki side, if you had previously raw unstructured logs exported they will be in a global structure in key _otel_raw_log. But all your OTEL attributes will be at the root level of this main JSON structure

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ Guillaume GILL (523e417)

[gramidt]

@gillg - Could you make this PR a DRAFT, since it's a WIP?

[gramidt]

Also, let's continue the discussion on the issue you created prior to finishing this PR, so we can ensure that we are all aligned on the solution. Thank you again for all of your help!

#2529

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This PR was marked stale due to lack of activity. It will be closed in 7 days.

[github-actions]

Closed as inactive. Feel free to reopen if this PR is still being worked on.

[gillg]

What are we doing about that ?

I disscussed about mandatory fields or not on the stable opentelemetry-collector project, and body, attributes are optional in the spec. So in my opinion we really should adapt sended fields to match with loki standards.
In loki we have "labels" and "log message" that's all. Both are separated, and independant, it means you can have a label "severity" without been present in the log itself.

By security we can't imagine automate to put attributes on labels, the curent approach of mapping is interesting and could be improved in the future. We could also do the same thing for "resources" in the future.

So in my opinion, push all attributes as a serialized JSON to loki, adding other top-level attributes _otel_XXXX in the map could be a not too dirty solution.