Tracing

OpenTelemetry baggage is a context-associated collection of string key-value pairs. It lets information known near a request’s entry point travel to downstream operations: a deployment region or a rollout cohort, for example. Unlike a span attribute, baggage is intended for propagation. Unlike trace context, it describes application-selected information rather than the identifiers and flags connecting spans. These mechanisms can travel together without being the same data structure. ...

BPF programs can attach to selected events in a running kernel without rebuilding the application or restarting its workload. A userspace loader still loads and manages the probe. Collection changes resource use, so “live” does not mean invisible or free. Other profilers can also observe running programs; choosing BPF depends on the question and available instrumentation. ...

Trace sampling selects which recorded work reaches the tracing pipeline. It can reduce export traffic and storage, but a configured percentage is not a strict ceiling on bytes, processor time, or money. Requests produce different numbers of spans, attributes vary in size, and traffic itself changes. A one-percent policy applied to a sudden tenfold traffic increase can still produce roughly ten times as much sampled data. ...

A distributed trace connects recorded operations through a shared trace identifier and explicit relationships. A span represents one operation, with start and end timestamps, attributes, events, and status. This makes a trace useful when a checkout request crosses an application, an inventory service, and a payment service. The resulting picture depends on which operations were instrumented, retained, and exported; it is not an automatic inventory of every action the request performed. ...