# Round Robin and First Successful routers

*MuleSoft Platform Integration Architect Study Guide · Designing and developing Mule applications · Last updated November 13, 2026 · https://www.certifyforce.com/study-guide/mulesoft-platform-integration-architect/designing-and-developing-mule-applications/round-robin-and-first-successful-routers*

How the four core Flow Control routers differ (Choice, Scatter-Gather, Round Robin and First Successful), with the full behavior of Round Robin and First Successful: route selection, event propagation and what an outer error handler must expect.

- Certification: Salesforce MuleSoft Platform Integration Architect
- Exam section: Designing and developing Mule applications
- Study guide: https://www.certifyforce.com/study-guide/mulesoft-platform-integration-architect

**Official exam objective:**

> Design Mule applications using core routers available to all Mule applications.

## What the exam expects

- Pick the core router that matches a routing requirement: one route by condition, every route in parallel, one route per event in turn, or routes tried in order until one succeeds.
- Predict which Round Robin route an event takes and what the processor after the router receives.
- Predict First Successful's behavior when a route fails, when one succeeds, and when every route fails.
- Design the outer error handling for a router, using the error types each router documents.

**Flow Control component (router):** a core component that takes the input Mule event and routes it to one or more separate sequences of components. **Route:** a scope inside a router that holds one or more processors. **Round Robin:** runs exactly one of two or more routes per execution, keeping track of the previous route. **First Successful:** iterates through routes until one executes without error. **MULE:ROUTING:** the core error type for an error while routing a message ([Core Components](https://docs.mulesoft.com/mule-runtime/latest/about-components), [Round Robin](https://docs.mulesoft.com/mule-runtime/latest/round-robin), [First Successful](https://docs.mulesoft.com/mule-runtime/latest/first-successful), [Errors Overview](https://docs.mulesoft.com/mule-runtime/latest/mule-error-concept)).

## Key facts

| Fact | Detail | Source |
|---|---|---|
| Round Robin routes | Two or more; one runs per execution | [Round Robin](https://docs.mulesoft.com/mule-runtime/latest/round-robin) |
| Round Robin selection | Tracks the previous route; never the same route twice in a row; wraps to the first | [Round Robin](https://docs.mulesoft.com/mule-runtime/latest/round-robin) |
| Round Robin event changes | Propagate to the processor after the router | [Round Robin](https://docs.mulesoft.com/mule-runtime/latest/round-robin) |
| Round Robin Business Events | `tracking:enable-default-events`, default false | [Round Robin](https://docs.mulesoft.com/mule-runtime/latest/round-robin) |
| Round Robin throws | `MULE:ROUTING` | [Round Robin](https://docs.mulesoft.com/mule-runtime/latest/round-robin) |
| First Successful on route error | Executes the next route | [First Successful](https://docs.mulesoft.com/mule-runtime/latest/first-successful) |
| First Successful after a success | Stops; later routes do not run | [First Successful](https://docs.mulesoft.com/mule-runtime/latest/first-successful) |
| First Successful with no success | Throws an error (type not named on the page) | [First Successful](https://docs.mulesoft.com/mule-runtime/latest/first-successful) |
| Choice | First true expression wins; default route otherwise | [Choice Router](https://docs.mulesoft.com/mule-runtime/latest/choice-router-concept) |
| Scatter-Gather failure | `MULE:COMPOSITE_ROUTING` after all routes run | [Scatter-Gather](https://docs.mulesoft.com/mule-runtime/latest/scatter-gather-concept) |

## Check yourself

- When the third route of the documentation's four-route First Successful example succeeds, what happens to the fourth route?
- When you plan a Choice router, which four aspects does the documentation say to consider?
- Which parts of the incoming Mule event can processors inside a Round Robin route read?

## Sources

- [Round Robin Router](https://docs.mulesoft.com/mule-runtime/latest/round-robin)
- [First Successful Router](https://docs.mulesoft.com/mule-runtime/latest/first-successful)
- [Core Components](https://docs.mulesoft.com/mule-runtime/latest/about-components)
- [Choice Router](https://docs.mulesoft.com/mule-runtime/latest/choice-router-concept)
- [Scatter-Gather Router](https://docs.mulesoft.com/mule-runtime/latest/scatter-gather-concept)
- [Errors Overview](https://docs.mulesoft.com/mule-runtime/latest/mule-error-concept)

## About the full unit

The "Core concepts", "Exam traps" and "Worked scenario" sections of this unit, its 2 linked practice questions, and unlimited timed mock exams are included with the MuleSoft Platform Integration Architect pack (USD $19): https://www.certifyforce.com/practice-exams