Planned lessonMID-028-L09

Demo: what a rebalance does to in-flight messages

On This Lesson 3 topics

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In this lesson

observe duplicate delivery on rebalance. Prepares MID-028-LAB1.

Draft outline details

Start two inventory consumers; note partition assignments.
Make the handler slow (5 s) and record each processed eventId.
Kill one consumer mid-processing; watch partitions reassign.
The surviving consumer re-reads from the last committed offset; show a message processed twice.
Planned mistake: enable auto-commit before processing and show a message lost on a crash. Fix by committing after processing.
Add an idempotency check on eventId and replay; the duplicate no longer has an effect.

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