The Distributed Tracing Working Group has published a First Public Working Draft of Propagation format for distributed trace context: Baggage. Distributed tracing is a set of tools and practices to monitor the health and reliability of a distributed application. A distributed application is an application that consists of multiple components that are deployed and operated separately. It is also known as micro-service.

The main concept behind distributed tracing is event correlation. Event correlation is a way to correlate events from one component to the events from another. It allows to find the cause-and-effect relationship between these events. For instance – find which user action in a browser caused a failure in the business logic layer.

To correlate events between components, these components need to exchange and store a piece of information called context. Typically context consists of an originating event identifier, an originating component identity and other event properties. Context has two parts. The first part is a trace context. Trace context consists of properties crucial for event correlation. The second part is baggage. Baggage carries user-defined properties. These properties may be helpful for correlation scenarios. But they are not required and components may choose to not carry or store them.

Unifying the format of distributed tracing context as well as aligning on semantic meaning of the values is the main objective of this working group. The goal is to share this with the community so that various tracing and diagnostics products can operate together.