Context propagation

With context propagation, signals can be correlated with each other, regardless of where they are generated. Although not limited to tracing, context propagation allows traces to build causal information about a system across services that are arbitrarily distributed across process and network boundaries.

To understand context propagation, you need to understand two separate concepts: context and propagation.

Context

Context is an object that contains the information for the sending and receiving service, or execution unit, to correlate one signal with another.

When Service A calls Service B, it includes a trace ID and a span ID as part of the context. Service B uses these values to create a new span that belongs to the same trace, setting the span from Service A as its parent. This makes it possible to track the full flow of a request across service boundaries.

Propagation

Propagation is the mechanism that moves context between services and processes. It serializes or deserializes the context object and provides the relevant information to be propagated from one service to another.

Propagation is usually handled by instrumentation libraries and is transparent to the user. In the event that you need to manually propagate context, you can use the Propagators API.

OpenTelemetry maintains several official propagators. The default propagator is using the headers specified by the W3C TraceContext specification.

Specification

To learn more about Context Propagation, see the Context specification.