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In a well-run Kafka deployment, controller ports, like ZooKeeper ports, should be firewalled off from clients.  This will prevent clients from disrupting the cluster by flooding the controller ports with requests.  In the realm of ACLs, this translates to controllers requiring CLUSTERACTION on CLUSTER for all operations.  (KIP-590 describes how users' administrative requests will be forwarded to the controller quorum as needed.)

The only time when clients should contact a controller node directly is when they are debugging system issues.  This is similar to ZooKeeper, where we have things like zk-shell, but only for debugging.

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