Traces don't respect X-Cloud-Trace-Context

[johnpena]

Using the latest version of the stackdriver exporter, traces that are exported don't respect the request's "X-Cloud-Trace-Context" header when determining the TraceID for the trace/span. This makes it not possible to correlate traces and logs in environments like AppEngine and Cloud Run, for which the load balancer sets the header before forwarding the request to the container.

Ideally, if a workaround can be provided in the meantime, that would be appreciated.