XCorrelationID

XCorrelationID is a non-standard HTTP header used in distributed software systems to carry a unique identifier that can be used to correlate a single request as it flows through multiple services. The header enables end-to-end tracing by tying together logs, metrics, and events from different components that handle the same user request.

Usage and propagation: A client may supply a correlation ID in XCorrelationID, or a server gateway or originating service may generate one if the header is absent. As the request moves between services, the same header value should be passed along in downstream calls to maintain continuity of the trace. This facilitates troubleshooting and performance analysis across microservices or distributed architectures.

Format and generation: The value is typically a UUID or another opaque token. Because XCorrelationID is not standardized, implementations treat the header as a flexible string, often using a version 4 UUID for simplicity and uniqueness. It is generally advisable to keep the value URL-safe and free of sensitive data.

Relation to other tracing standards: XCorrelationID is distinct from standardized tracing mechanisms such as the W3C Trace Context's traceparent header. While XCorrelationID can be used independently, many organizations use it alongside formal tracing tools to improve visibility across services. It is especially common in systems that do not yet adopt a full tracing stack.

Best practices and considerations: Generate high-entropy identifiers, propagate the header through all internal and asynchronous calls, and consistently log the correlation ID in all related logs. Treat the value as opaque and avoid embedding sensitive user data. Consider privacy, data retention, and compatibility with logging and monitoring pipelines when introducing XCorrelationID.