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Kafka has a dependency on Zookeeper 3.6.3, which reached its end of life in December 2022. We would like to upgrade Zookeeper to version 3.8.1 which is the latest release of the 3.8.x versions.

Zookeeper 3.8.1 server supports clients no older than 3.5.x (i.e. Apache Kafka version 2.4.0) and Zookeeper 3.8.1. clients support server versions no older than 3.5.x (i.e. Apache Kafka version 2.4.0).

ZooKeeper clients from 3.5.x onwards are fully compatible with 3.8.x servers.
The upgrade from 3.6.x and 3.7.x can be executed as usual, no particular additional upgrade procedure is needed.
ZooKeeper 3.8.x clients are compatible with 3.5.x, 3.6.x and 3.7.x servers as long as you are not using new APIs not present these versions.

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Users who use Kafka clusters with Zookeeper clients older than 3.5.x won't be able to communicate with a Zookeeper cluster using 3.8.1. As mentioned in the accompanying JIRA ticket Apache Kafka has been using Zookeeper 3.5.x since version 2.4 so versions above and including it should be safe for this upgrade. It is acceptable to break compatibility with Apache Kafka versions prior to 2.4 as they are considered beyond their end of life and are not maintained. (source: Time Based Release Plan#WhatIsOurEOLPolicy).

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