Page History

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                                                                    -- (reject) -->    Consumer (register failed due to some invalid meta info, try to reconnect to the coordinator and register again)

Detecting consumer failure. For every registered consumer, the coordinator will try to check its liveness by periodic pinging it. The replied ping response should include the partition consumed offfset if auto-offset-commit is enabled. If the consumer fails to reply the ping request for a configurable number of times. The coordinator will mark the consumer as failed and trigger the rebalance procedure for the group this consumer belongs to.

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                                (rebalance)         time out...         Consumer (failed)

Detecting changes to topic partitions. The coordinator keeps a watch for every registered partitions stored in brokers. When a new partition is added (possibly due to a new added broker) or an old partition is deleted (possibly due to a broker failure). It will trigger the rebalance procedure for every group that is consuming this partition.

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(retry rebalance)  time out...        Consumer (failed)

When a coordinator is failed, other peer brokers will notice that and try to re-elect to be the new coordinator. The new coordinator will not try to connect to the consumers but wait for the consumers to realize the previous coordinator has dead and try to re-connect to itself.

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