Use trace id generated by upstream

Sometimes you want to use trace ids (or request ids) generated earlier during the request to have log correlation across the entire stack.

For example:

Nginx: if you want to correlate symfony app logs with Nginx access logs, you could use the requestId generated by Nginx as a trace id
Google Cloud Platform Load Balancers: Google's LBs set a X-Cloud-Trace-Context header on each request. If you want to use it to correlate logs including GCP Cloud LB logs, Nginx and Symfony logs, use the following configuration:

instrumentation:
  tracing:
    request:
      incoming_header:
        name: x-cloud-trace-context
        regex: /^(?<trace>[A-Za-z0-9]{32})(\/(?<span>[A-Za-z0-9]*);?(?<options>((o=(?<sampled>[A-Za-z0-1]*))))?)?$/