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https://issues.apache.org/jira/browse/HADOOP-16579?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Mate Szalay-Beko updated HADOOP-16579:
--------------------------------------
    Summary: Upgrade to Apache Curator 4.2.0 and ZooKeeper 3.5.6 in Hadoop  
(was: Upgrade to Apache Curator 4.2.0 in Hadoop)

> Upgrade to Apache Curator 4.2.0 and ZooKeeper 3.5.6 in Hadoop
> -------------------------------------------------------------
>
>                 Key: HADOOP-16579
>                 URL: https://issues.apache.org/jira/browse/HADOOP-16579
>             Project: Hadoop Common
>          Issue Type: Improvement
>            Reporter: Mate Szalay-Beko
>            Assignee: Norbert Kalmár
>            Priority: Major
>
> Currently in Hadoop we are using [ZooKeeper version 
> 3.4.13|https://github.com/apache/hadoop/blob/7f9073132dcc9db157a6792635d2ed099f2ef0d2/hadoop-project/pom.xml#L90].
>  ZooKeeper 3.5.5 is the latest stable Apache ZooKeeper release. It contains 
> many new features (including SSL related improvements which can be very 
> important for production use; see [the release 
> notes|https://zookeeper.apache.org/doc/r3.5.5/releasenotes.html]).
> Apache Curator is a high level ZooKeeper client library, that makes it easier 
> to use the low level ZooKeeper API. Currently [in Hadoop we are using Curator 
> 2.13.0|https://github.com/apache/hadoop/blob/7f9073132dcc9db157a6792635d2ed099f2ef0d2/hadoop-project/pom.xml#L91]
>  and [in Ozone we use Curator 
> 2.12.0|https://github.com/apache/hadoop/blob/7f9073132dcc9db157a6792635d2ed099f2ef0d2/pom.ozone.xml#L146].
> Curator 2.x is supporting only the ZooKeeper 3.4.x releases, while Curator 
> 3.x is compatible only with the new ZooKeeper 3.5.x releases. Fortunately, 
> the latest Curator 4.x versions are compatible with both ZooKeeper 3.4.x and 
> 3.5.x. (see [the relevant Curator 
> page|https://curator.apache.org/zk-compatibility.html]). Many Apache projects 
> have already migrated to Curator 4 (like HBase, Phoenix, Druid, etc.), other 
> components are doing it right now (e.g. Hive).
> *The aims of this task are* to:
>  - change Curator version in Hadoop to the latest stable 4.x version 
> (currently 4.2.0)
>  - also make sure we don't have multiple ZooKeeper versions in the classpath 
> to avoid runtime problems (it is 
> [recommended|https://curator.apache.org/zk-compatibility.html] to exclude the 
> ZooKeeper which come with Curator, so that there will be only a single 
> ZooKeeper version used runtime in Hadoop)
> In this ticket we still don't want to change the default ZooKeeper version in 
> Hadoop, we only want to make it possible for the community to be able to 
> build / use Hadoop with the new ZooKeeper (e.g. if they need to secure the 
> ZooKeeper communication with SSL, what is only supported in the new ZooKeeper 
> version). Upgrading to Curator 4.x should keep Hadoop to be compatible with 
> both ZooKeeper 3.4 and 3.5.



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