What is the correct way to send a custom correlation ID from the client to multiple Mule applications via HTTP?

• A. Set the HTTP header correlationId with a UUID
• B. Use a query parameter correlation_id in each request
• C. Set the HTTP header x-correlation-id with each request to the app name plus a UUID
• D. Store the correlation ID in a cookie

Answer: (C)

Propagating a single, unique correlation identifier with the request is what makes tracing across multiple Mule applications reliable. Using the HTTP header X-Correlation-ID ensures the ID travels with the HTTP call as it moves from one service to another, even through gateways or proxies. The value is typically a UUID, and including the originating app name as part of the value helps you quickly recognize where the trace started. This approach is robust for service-to-service communication, unlike putting the ID in a query parameter (which can be dropped or altered by intermediaries) or in a cookie (which is browser-focused and not reliably sent by non-browser clients). By consistently sending the header and forwarding it downstream, each Mule app can log and correlate its part of the flow, giving you end-to-end visibility.