Log parsed trace_id from traceparent header

[takotakot]

It's currently difficult to correlate distributed requests across services using only logs. While the traceparent header (W3C Trace Context) provides the necessary context, directly logging the trace_id component would be the most effective way to enable log-based trace correlation.

When an incoming HTTP request contains the traceparent header:

1. Parse the header value according to the W3C Trace Context specification.
2. Extract the trace_id portion.
3. Include this extracted trace_id value in the corresponding request log entry.

For example, if the header is traceparent="00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01", the log entry should include a field like trace_id="0af7651916cd43dd8448eb211c80319c".

Logging the full traceparent string is an alternative, but logging just the trace_id is often sufficient for correlation and can result in slightly cleaner/more focused log entries.

This allows direct filtering and searching of logs using the trace_id in log aggregation systems, significantly improving debugging capabilities and observability for distributed traces.

c.f.
Some cloud providers support their own log format for trace id:
Google Cloud "trace" or "logging.googleapis.com/trace" Structured logging
AWS aws.cloudwatch_logs.log_group AWS resource data