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Apache Hadoop ${project.version}
================================

Apache Hadoop ${project.version} is a point release in the 2.x.y release
line, building upon the previous stable release 2.8.4.

Here is a short overview of the major features and improvements.

*   Common

    *   Support async call retry and failover which can be used in async DFS
        implementation with retry effort.

    *   Cross Frame Scripting (XFS) prevention for UIs can be provided through
        a common servlet filter.

    *   S3A improvements: add ability to plug in any AWSCredentialsProvider,
        support read s3a credentials from hadoop credential provider API in
        addition to XML configuraiton files, support Amazon STS temporary
        credentials

    *   WASB improvements: adding append API support

    *   Build enhancements: replace dev-support with wrappers to Yetus,
        provide a docker based solution to setup a build environment,
        remove CHANGES.txt and rework the change log and release notes.

    *   Add posixGroups support for LDAP groups mapping service.

*   HDFS

    *   WebHDFS enhancements: integrate CSRF prevention filter in WebHDFS,
        support OAuth2 in WebHDFS, disallow/allow snapshots via WebHDFS

    *   Allow long-running Balancer to login with keytab

    *   Add ReverseXML processor which reconstructs an fsimage from an XML file.
        This will make it easy to create fsimages for testing, and manually edit
        fsimages when there is corruption

    *   Support nested encryption zones

    *   DataNode Lifeline Protocol: an alternative protocol for reporting DataNode
        liveness. This can prevent the NameNode from incorrectly marking DataNodes
        as stale or dead in highly overloaded clusters where heartbeat processing
        is suffering delays.

    *   Logging HDFS operation's caller context into audit logs

    *   A new Datanode command for evicting writers which is useful when data node
        decommissioning is blocked by slow writers.

*   YARN

    *   NodeManager CPU resource monitoring in Windows.

    *   NM shutdown more graceful: NM will unregister to RM immediately rather than
        waiting for timeout to be LOST (if NM work preserving is not enabled).

    *   Add ability to fail a specific AM attempt in scenario of AM attempt get stuck.

    *   CallerContext support in YARN audit log.

    *   ATS versioning support: a new configuration to indicate timeline service version.

*   MAPREDUCE

    *   Allow node labels get specified in submitting MR jobs

    *   Add a new tool to combine aggregated logs into HAR files

Getting Started
===============

The Hadoop documentation includes the information you need to get started using
Hadoop. Begin with the
[Single Node Setup](./hadoop-project-dist/hadoop-common/SingleCluster.html) which
shows you how to set up a single-node Hadoop installation. Then move on to the
[Cluster Setup](./hadoop-project-dist/hadoop-common/ClusterSetup.html) to learn how
to set up a multi-node Hadoop installation.