[DOCS] Add X-Pack node settings for Elasticsearch Reference (elastic/x-pack-elasticsearch#1688)

* [DOCS] Add X-Pack node settings for Elasticsearch Reference

* [DOCS] Fix callout in node.asciidoc

Original commit: elastic/x-pack-elasticsearch@9c29441734

docs/en/node.asciidoc

@@ -0,0 +1,118 @@
+[float]
+[[modules-node-xpack]]
+== [xpack]#X-Pack node settings#
+
+//This content is referenced from the elastic/elasticsearch/docs/reference/modules/node.asciidoc
+
+If {xpack} is installed, there is an additional node type:
+
+<<ml-node,Machine learning node>>::
+
+A node that has `xpack.ml.enabled` and `node.ml` set to `true`, which is the
+default behavior when {xpack} is installed. If you want to use {xpackml}
+features, there must be at least one {ml} node in your cluster. For more
+information about {xpackml} features,
+see {xpack-ref}/xpack-ml.html[Machine Learning in the Elastic Stack].
+
+IMPORTANT: Do not set use the `node.ml` setting unless {xpack} is installed.
+Otherwise, the node fails to start.
+
+If {xpack} is installed, nodes are master-eligible, data, ingest, and {ml}
+nodes by default. As the cluster grows and in particular if you have large
+{ml} jobs, consider separating dedicated master-eligible nodes from dedicated
+data nodes and dedicated {ml} nodes.
+
+To create a standalone master-eligible node when {xpack} is installed, set:
+
+[source,yaml]
+-------------------
+node.master: true <1>
+node.data: false <2>
+node.ingest: false <3>
+node.ml: false <4>
+xpack.ml.enabled: true <5>
+-------------------
+<1> The `node.master` role is enabled by default.
+<2> Disable the `node.data` role (enabled by default).
+<3> Disable the `node.ingest` role (enabled by default).
+<4> Disable the `node.ml` role (enabled by default in {xpack}).
+<5> The `xpack.ml.enabled` setting is enabled by default in {xpack}.
+
+To create a dedicated data node when {xpack} is installed, set:
+
+[source,yaml]
+-------------------
+node.master: false <1>
+node.data: true <2>
+node.ingest: false <3>
+node.ml: false <4>
+-------------------
+<1> Disable the `node.master` role (enabled by default).
+<2> The `node.data` role is enabled by default.
+<3> Disable the `node.ingest` role (enabled by default).
+<4> Disable the `node.ml` role (enabled by default in {xpack}).
+
+To create a dedicated ingest node when {xpack} is installed, set:
+
+[source,yaml]
+-------------------
+node.master: false <1>
+node.data: false <2>
+node.ingest: true <3>
+search.remote.connect: false <4>
+node.ml: false <5>
+-------------------
+<1> Disable the `node.master` role (enabled by default).
+<2> Disable the `node.data` role (enabled by default).
+<3> The `node.ingest` role is enabled by default.
+<4> Disable cross-cluster search (enabled by default).
+<5> Disable the `node.ml` role (enabled by default in {xpack}).
+
+To create a dedicated coordinating node when {xpack} is installed, set:
+
+[source,yaml]
+-------------------
+node.master: false <1>
+node.data: false <2>
+node.ingest: false <3>
+search.remote.connect: false <4>
+node.ml: false <5>
+-------------------
+<1> Disable the `node.master` role (enabled by default).
+<2> Disable the `node.data` role (enabled by default).
+<3> Disable the `node.ingest` role (enabled by default).
+<4> Disable cross-cluster search (enabled by default).
+<5> Disable the `node.ml` role (enabled by default in {xpack}).
+
+[float]
+[[ml-node]]
+=== [xpack]#Machine learning node#
+
+The {xpackml} features provide {ml} nodes, which run jobs and handle {ml} API
+requests. If `xpack.ml.enabled` is set to true and `node.ml` is set to `false`,
+the node can service API requests but it cannot run jobs.
+
+If you want to use {xpackml} features in your cluster, you must enable {ml}
+(set `xpack.ml.enabled` to `true`) on all master-eligible nodes. Do not use
+these settings if you do not have {xpack} installed.
+
+For more information about these settings,
+see {xpack-ref}/ml-settings.html[Machine Learning Settings].
+
+To create a dedicated {ml} node, set:
+
+[source,yaml]
+-------------------
+node.master: false <1>
+node.data: false <2>
+node.ingest: false <3>
+search.remote.connect: false <4>
+node.ml: true <5>
+xpack.ml.enabled: true <6>
+-------------------
+<1> Disable the `node.master` role (enabled by default).
+<2> Disable the `node.data` role (enabled by default).
+<3> Disable the `node.ingest` role (enabled by default).
+<4> Disable cross-cluster search (enabled by default).
+<5> The `node.ml` role is enabled by default in {xpack}.
+<6> The `xpack.ml.enabled` setting is enabled by default in {xpack}.