# Message correlation across integration boundaries

*MuleSoft Developer II Study Guide · Implement monitorable Mule applications · Last updated November 7, 2026 · https://www.certifyforce.com/study-guide/mulesoft-developer-ii/implement-monitorable-mule-applications/message-correlation-across-integration-boundaries*

Follow event correlation across sources, scopes, error handlers and HTTP calls, then preserve the required identifier explicitly when work is stored for replay.

- Certification: Salesforce MuleSoft Developer II
- Exam section: Implement monitorable Mule applications
- Study guide: https://www.certifyforce.com/study-guide/mulesoft-developer-ii

**Official exam objective:**

> Implement message correlation, including persistence and propagation of correlation IDs over HTTP.

## What the exam expects

- Distinguish source-supplied correlation from fallback generation.
- Predict the effective ID inside and outside a Tracing scope.
- Apply error-handler context when reading correlation evidence.
- Persist and restore the required ID through an explicit replay contract.
- Configure HTTP transmission separately from selecting the outgoing value.

A **correlation ID** identifies an event execution; a **generator** creates a fallback identifier; a **Tracing scope** temporarily changes the effective identifier; **propagation** transmits it across a boundary; **persistence** retains it for later work. Runtime behavior here follows Mule4.6, with HTTP1.9 controls.

## Key facts

| Fact | Detail | Source |
|---|---|---|
| Source fallback | Generation is used when the source supplies no ID. | [Correlation ID](https://docs.mulesoft.com/mule-runtime/4.6/correlation-id) |
| Generator obligation | Different events must not receive duplicate generated IDs. | [Correlation ID](https://docs.mulesoft.com/mule-runtime/4.6/correlation-id) |
| Scoped override | Normal completion restores the preceding correlation context. | [Correlation ID](https://docs.mulesoft.com/mule-runtime/4.6/correlation-id) |
| Handler context | The containing flow or Try determines the handler's ID. | [Correlation ID](https://docs.mulesoft.com/mule-runtime/4.6/correlation-id) |
| Durable replay | Persist the required string and explicitly apply it to replay work. | [Correlation ID](https://docs.mulesoft.com/mule-runtime/4.6/correlation-id) |
| Send control | Governs inclusion for custom and event-derived outgoing values. | [HTTP1.9 reference](https://raw.githubusercontent.com/mulesoft/docs-connectors/33276ccdb80668dd8bd45102a529a5fcc0918eea/http/1.9/modules/ROOT/pages/http-documentation.adoc) |
| Request value | The operation Correlation Id field selects a custom value. | [HTTP1.9 reference](https://raw.githubusercontent.com/mulesoft/docs-connectors/33276ccdb80668dd8bd45102a529a5fcc0918eea/http/1.9/modules/ROOT/pages/http-documentation.adoc) |
| Log reconstruction | Event identity is independent of the displayed worker thread. | [Correlation ID](https://docs.mulesoft.com/mule-runtime/4.6/correlation-id) |

## Check yourself

- Why can a correlation ID help an investigation beyond ordinary log searching?
- When does the runtime guide identify a genuine reason to consider generator customization?
- What configuration context can the illustrated extra correlation diagnostics provide?

## Sources

- [Correlation ID, Mule4.6](https://docs.mulesoft.com/mule-runtime/4.6/correlation-id)
- [HTTP Connector1.9 reference](https://raw.githubusercontent.com/mulesoft/docs-connectors/33276ccdb80668dd8bd45102a529a5fcc0918eea/http/1.9/modules/ROOT/pages/http-documentation.adoc)
- [Configuring logging, Mule4.6](https://docs.mulesoft.com/mule-runtime/4.6/logging-in-mule)

## About the full unit

The "Core concepts", "Exam traps" and "Worked scenario" sections of this unit, its 8 linked practice questions, and unlimited timed mock exams are included with the MuleSoft Developer II pack (USD $19): https://www.certifyforce.com/practice-exams