Context Propagation

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

We define Context Propagation by two sub-concepts: Context and Propagation.

Context

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

For example, if Service A calls Service B, then a span from Service A whose ID is in context will be used as the parent span for the next span created in Service B. The trace ID that is in context will be used for the next span created in Service B as well, which signifies that the span is part of the same trace as the span from Service A.

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, but in the event that you need to manually propagate context, you can use Propagation APIs.

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.