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1. For each to-be-assigned source connector, if there is a set of task configurations present in the config topic after the most recent task count record for that connector:
1. If there is an existing task count record for the connector in the config topic, and either the task count in that record is above 1 or the new number of tasks for the connector is above 1*:
   1. Fence out all producers that may still be active for prior task instances of this connector by instantiating an admin client using the connector principal and invoking Admin::fenceProducers (a new API described below; see Admin API to Fence out Transactional Producers). The transactional IDs will be the IDs that each task of the connector would have used, assuming as many tasks were active as the most recent task count record for the connector.** 
2. Write the new task count record for all of the fenced-out connectors to the config topic
2. Read to the end of the config topic to verify that all task count records have been written successfully, and use the new latest offset of the config topic as the offset in the assignment given out to members of the cluster.

* - The check for task counts is done to avoid unnecessary fencing work for permanently single-task connectors, such as Debezium's CDC source connectors. If the most recent task count record for a connector shows one task, there is only one task that needs to be fenced out. And, if the new configuration for that connector contains one task, that new task will automatically fence out its single predecessor as they will use the same transactional ID. 

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1. Worker is assigned a source task during rebalance
2. If there is no task count record present in the config topic for that connector, or there is a set of task configurations present after the latest task count record, refuse to bring up the task and await a subsequent rebalance
3. Otherwise:
   1. Instantiate a transactional producer for the task
   2. Read to the end of the config topic
   3. If a new set of task configurations has since been generated for the connector, abort startupabandon startup *
   4. Otherwise, begin polling the task for data

* - If this happens, a new task will be automatically brought up in place of this task, in response to the new set of task configurations in the config topic. No action (such as restarting the task) will be necessary on the part of the user.

Leader access to config topic

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