How would you explain Consumer Groups and Rebalance to a junior engineer?

Answers use simple, clear English.

Quick interview answer

Explain Consumer Groups and Rebalance in one sentence, then a tiny example, then one “don’t do this” tip. Baseline: Each partition consumed by one consumer in group. Rebalance on member join/leave — can cause duplicate processing if offsets not committed carefully.

Detailed answer

Junior-friendly explanation of Consumer Groups and Rebalance: Plain English: Baseline: Each partition consumed by one consumer in group. Rebalance on member join/leave — can cause duplicate processing if offsets not committed carefully. Tiny example: 6 partitions, 3 consumers → each gets 2 partitions; add 4th consumer triggers rebalance. One warning: Long processing without pause; committing before side effects complete.

Full explanation

Keep jargon low, then layer detail. Each partition consumed by one consumer in group. Rebalance on member join/leave — can cause duplicate processing if offsets not committed carefully.

Follow-up questions

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Parent context — Consumer Groups and Rebalance

Baseline: Each partition consumed by one consumer in group. Rebalance on member join/leave — can cause duplicate processing if offsets not committed carefully.

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