In Application Performance Monitoring (APM), where is the span context information located during transfer?

In Oracle Cloud Infrastructure Application Performance Monitoring (APM) and distributed tracing frameworks (such as OpenTelemetry and W3C Trace Context standards), span context is propagated across distributed microservices by injecting tracing metadata into the HTTP header of outgoing network requests. When a service makes a call to another service or API, the APM tracer attaches span identifiers, trace IDs, and execution sampling flags directly to HTTP headers (such as traceparent). The receiving microservice extracts this context from the incoming HTTP header to continue the trace, enabling seamless end-to-end transaction tracking across distributed application components and service boundaries.

A. Service boundaries represent logical transitions where tracing context is passed, but the physical location of the context data during transfer is inside the request headers.
C. An HTTP call is the overall communication action, whereas the span context specifically resides inside the HTTP header payload metadata.
D. Browsers and microservices are execution environments where spans are created or extracted, not the transit mechanism or location of context during transfer.

1. Oracle Cloud Infrastructure Documentation, "Application Performance Monitoring", Section: Trace Context Propagation and HTTP Headers.

2. W3C Recommendation, "W3C Trace Context", Section: HTTP Header Field Definitions. https://www.w3.org/TR/trace-context/