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.
Design Mule applications using core routers available to all Mule applications.
~6 min read · 2 practice questions
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, Round Robin, First Successful, Errors Overview).
Key facts
- Detail
- Two or more; one runs per execution
- Detail
- Tracks the previous route; never the same route twice in a row; wraps to the first
- Detail
- Propagate to the processor after the router
- Detail
tracking:enable-default-events, default false
- Detail
MULE:ROUTING
- Detail
- Executes the next route
- Detail
- Stops; later routes do not run
- Detail
- Throws an error (type not named on the page)
- Detail
- First true expression wins; default route otherwise
- Detail
MULE:COMPOSITE_ROUTINGafter all routes run
- 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?
The questions are free to read. Answers with their sources and self-grading are included with the pack.
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