What is a Scatter-Gather router and how does it work?

• A. Splits a message into multiple parallel branches and aggregates results.
• B. Joins multiple messages into a single stream.
• C. Filters messages based on content.
• D. Retries failed messages.

Answer: (C)

Scatter-Gather fans out a single message to multiple parallel branches (scatter) and then collects the results into one message (gather/aggregate). It splits the work so each branch can run concurrently, and once all branches finish, their outputs are merged into a single payload by the aggregator. This is useful when you need to call several services or perform independent computations in parallel and then combine the results.

The other descriptions don’t fit this pattern: filtering or selecting messages based on content is done with a Filter or Choice, not by scattering and gathering. Joining multiple messages into a single stream describes a merge or concatenation pattern, which is different from running parallel branches and aggregating their results. Retrying failed messages relates to fault tolerance and error handling, not to distributing work across parallel routes.