[[repository-hdfs]]
=== Hadoop HDFS Repository Plugin

The HDFS repository plugin adds support for using HDFS File System as a repository for
{ref}/modules-snapshots.html[Snapshot/Restore].

[[repository-hdfs-install]]
[float]
==== Installation

This plugin can be installed using the plugin manager using _one_ of the following packages:

[source,sh]
----------------------------------------------------------------
sudo bin/plugin install repository-hdfs
sudo bin/plugin install repository-hdfs-hadoop2
sudo bin/plugin install repository-hdfs-lite
----------------------------------------------------------------

The chosen plugin must be installed on every node in the cluster, and each node must
be restarted after installation.

[[repository-hdfs-remove]]
[float]
==== Removal

The plugin can be removed by specifying the _installed_ package using _one_ of the following commands:

[source,sh]
----------------------------------------------------------------
sudo bin/plugin remove repository-hdfs
sudo bin/plugin remove repository-hdfs-hadoop2
sudo bin/plugin remove repository-hdfs-lite
----------------------------------------------------------------

The node must be stopped before removing the plugin.

[[repository-hdfs-usage]]
==== Getting started with HDFS

The HDFS snapshot/restore plugin comes in three _flavors_:

* Default / Hadoop 1.x::
The default version contains the plugin jar alongside Apache Hadoop 1.x (stable) dependencies.
* YARN / Hadoop 2.x::
The `hadoop2` version contains the plugin jar plus the Apache Hadoop 2.x (also known as YARN) dependencies.
* Lite::
The `lite` version contains just the plugin jar, without any Hadoop dependencies. The user should provide these (read below).

[[repository-hdfs-flavor]]
===== What version to use?

It depends on whether Hadoop is locally installed or not and if not, whether it is compatible with Apache Hadoop clients.

* Are you using Apache Hadoop (or a _compatible_ distro) and do not have installed on the Elasticsearch nodes?::
+
If the answer is yes, for Apache Hadoop 1 use the default `repository-hdfs` or `repository-hdfs-hadoop2` for Apache Hadoop 2.
+
* If you are have Hadoop installed locally on the Elasticsearch nodes or are using a certain distro::
+
Use the `lite` version and place your Hadoop _client_ jars and their dependencies in the plugin folder under `hadoop-libs`.
For large deployments, it is recommended to package the libraries in the plugin zip and deploy it manually across nodes 
(and thus avoiding having to do the libraries setup on each node).

[[repository-hdfs-security]]
==== Handling JVM Security and Permissions

Out of the box, Elasticsearch runs in a JVM with the security manager turned _on_ to make sure that unsafe or sensitive actions
are allowed only from trusted code. Hadoop however is not really designed to run under one; it does not rely on privileged blocks
to execute sensitive code, of which it uses plenty.

The `repository-hdfs` plugin provides the necessary permissions for both Apache Hadoop 1.x and 2.x (latest versions) to successfully
run in a secured JVM as one can tell from the number of permissions required when installing the plugin.
However using a certain Hadoop File-System (outside DFS), a certain distro or operating system (in particular Windows), might require 
additional permissions which are not provided by the plugin.

In this case there are several workarounds:
* add the permission into `plugin-security.policy` (available in the plugin folder)

* disable the security manager through `es.security.manager.enabled=false` configurations setting - NOT RECOMMENDED

If you find yourself in such a situation, please let us know what Hadoop distro version and OS you are using and what permission is missing
by raising an issue. Thank you!

[[repository-hdfs-config]]
==== Configuration Properties

Once installed, define the configuration for the `hdfs` repository through `elasticsearch.yml` or the
{ref}/modules-snapshots.html[REST API]:

[source,yaml]
----
repositories
  hdfs:
    uri: "hdfs://<host>:<port>/"    \# optional - Hadoop file-system URI
    path: "some/path"               \# required - path with the file-system where data is stored/loaded
    load_defaults: "true"           \# optional - whether to load the default Hadoop configuration (default) or not
    conf_location: "extra-cfg.xml"  \# optional - Hadoop configuration XML to be loaded (use commas for multi values)
    conf.<key> : "<value>"          \# optional - 'inlined' key=value added to the Hadoop configuration
    concurrent_streams: 5           \# optional - the number of concurrent streams (defaults to 5)
    compress: "false"               \# optional - whether to compress the metadata or not (default)
    chunk_size: "10mb"              \# optional - chunk size (disabled by default)
    
----

NOTE: Be careful when including a paths within the `uri` setting; Some implementations ignore them completely while
others consider them. In general, we recommend keeping the `uri` to a minimum and using the `path` element instead.

[[repository-hdfs-other-fs]]
==== Plugging other file-systems

Any HDFS-compatible file-systems (like Amazon `s3://` or Google `gs://`) can be used as long as the proper Hadoop
configuration is passed to the Elasticsearch plugin. In practice, this means making sure the correct Hadoop configuration
files (`core-site.xml` and `hdfs-site.xml`) and its jars are available in plugin classpath, just as you would with any
other Hadoop client or job.

Otherwise, the plugin will only read the _default_, vanilla configuration of Hadoop and will not be able to recognized
the plugged-in file-system.
