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We need a way to be able to stop users from creating a namespace after upgrading a subset of brokers, not all brokers. This will probably lead to inconsistent behavior. I do not have any suggestion on how to handle this, however one One easy way to handle this is to doc it.

Handling Acls Inheritance

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Handling Regexes in Topic Subscription

Pros

1. Will not change existing behavior.
2. No impact on upgrades.

Cons

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Regexes should work fine, however users might have to modify their existing regexes based on topics and namespaces that exist in the cluster. If someone, like mirrormaker, is subscribing to ".*", then this will just work fine and nothing has to be changed. However, if someone has regex like "bla*" and we end up having a namespace "bla", then they will get subscribed to topics that they were probably not expecting.

Compatibility, Deprecation, and Migration Plan

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