nginx: design question: Why does the sampler default to parent_based=false?

Hi,

I'm writing an OpenTelemetry TracerProvider implementation that is a wrapper around Datadog's tracing library. My intention is to eventually add support for that provider in this project's instrumentation/nginx module.

I notice that in the sampling configuration, sampler.parent_based defaults to false, which means that while nginx will extract trace context from an incoming request, it will by default not honor the sampling decision included in that context. Instead it will make its own sampling decision (which defaults to "always on").

Why was this chosen as the default? In the hypothetical Datadog case, I'd prefer parent_based to default to true.

@johanneswuerbach, the author of the configurable sampler.

Start with instrumentation/nginx/src/agent_config.h at the referenced sampling default and review the sampling configuration from pull request #26. Trace how parent_based is applied when incoming context is extracted, then examine the linked OpenTelemetry and Datadog provider context. Done means establishing and documenting whether the default should change.