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While this release will not remove ZooKeeper, it will eliminate most of the touch points where the rest of the system communicates with it.  As much as possible, we will perform all access to ZooKeeper in the controller, rather than in other brokers, clients, or tools.  Therefore, although ZooKeeper will still be required for the bridge release, it will be a well-isolated dependency.

We will be able to upgrade from any version of Kafka to this bridge release, and from the bridge release to a post-ZK release.  When upgrading from an earlier release to a post-ZK release, the upgrade must be done in two steps: first, you must upgrade to the bridge release, and then you must upgrade to the post-ZK release.

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