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Note: if an existing application is upgrade, users won't be affected, because if internal replication/changleog topics exist already, no create topic request would be sent anyway. Only if a new application is deployed, or if an existing application is reset, and thus repartition/changelog topics would need to be created users might be affected. Because the application won't startup for this case, the impact is minor and can be considered non-critical. Applications already running in production won't break.

We also believe that 2.3.0 broker a sufficiently old such that not too many user may be affectedEven if it's unclear how many users might be affected because they use older brokers than 2.4.0, and we want to take to opportunity of a major release to make this change (as it's technically breaking backward compatibility).

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