[DOCS] Added X-Pack monitoring to Elasticsearch Reference (elastic/x-pack-elasticsearch#2831)

Original commit: elastic/x-pack-elasticsearch@123738556e

docs/en/index.asciidoc

@@ -23,6 +23,9 @@ include::release-notes/xpack-breaking.asciidoc[]
 :edit_url:
 include::{es-repo-dir}/reference/index-shared3.asciidoc[]
 
+:edit_url!:
+include::monitoring/index.asciidoc[]
+
 :edit_url!:
 include::rest-api/index.asciidoc[]
 

docs/en/monitoring/http-export.asciidoc

@@ -0,0 +1,52 @@
+[role="xpack"]
+[[http-exporter]]
+== HTTP Exporter
+
+When you configure
+an exporter in `elasticsearch.yml`, the default `local` exporter is disabled.
+
+The `http` exporter uses the low-level {es} REST Client. This allows
+the `http` exporter to send its data to any {es} cluster it can access
+through the network.
+
+The `http` exporter supports a number of settings that control how it
+communicates over HTTP to remote clusters. In most cases, it is not
+necessary to explicitly configure these settings. For detailed
+descriptions, see {ref}/monitoring-settings.html[Monitoring Settings].
+
+[source,yaml]
+----------------------------------
+xpack.monitoring.exporters:
+  my_local: <1>
+    type: local
+  my_remote: <2>
+    type: http
+    host: [ "10.1.2.3", ... ] <3>
+    auth: <4>
+      username: my_username
+      password: changeme
+    connection:
+      timeout: 6s
+      read_timeout: 60s
+    ssl: ... <5>
+    proxy:
+      base_path: /some/base/path <6>
+    headers: <7>
+      My-Proxy-Header: abc123
+      My-Other-Thing: [ def456, ... ]
+    index.name.time_format: YYYY-MM <8>
+
+----------------------------------
+<1> A `local` exporter defined explicitly whose arbitrary name is `my_local`.
+<2> An `http` exporter defined whose arbitrary name is `my_remote`.
+<3> `host` is a required setting for `http` exporters, which can take a few
+    different forms as described in the table below.
+<4> User authentication for those using {security} or some other
+    form of user authentication protecting the cluster.
+<5> See below for all TLS / SSL settings. If not supplied, the default
+    node-level TLS / SSL settings will be used.
+<6> Optional base path to prefix any outgoing request with in order to
+    work with proxies.
+<7> Arbitrary key/value pairs to define as headers to send with every request.
+    The array-based key/value format sends one header per value.
+<8> A mechanism for changing the date suffix used by default.

docs/en/monitoring/index.asciidoc

@@ -0,0 +1,23 @@
+[role="xpack"]
+[[es-monitoring]]
+= Monitoring {es}
+
+[partintro]
+--
+{monitoring} enables you to easily monitor the health of your {es} cluster. The
+monitoring metrics are collected from each node and stored in {es} indices. You
+can then view the data from {kib} where it’s easy to spot issues at a glance or
+delve into the system behavior over time to diagnose operational issues. In
+addition to the built-in status warnings, you can also set up custom alerts
+based on the data in the monitoring indices.
+
+This section focuses on the {es} monitoring infrastructure and setup. For an
+introduction to monitoring your Elastic stack, including Logstash and {kib}, see
+{xpack-ref}/xpack-monitoring.html[Monitoring the Elastic Stack].
+//For information about using the Monitoring UI, see Monitoring in the Kibana guide.
+
+--
+
+include::stats-export.asciidoc[]
+include::http-export.asciidoc[]
+include::tribe.asciidoc[]

docs/en/monitoring/stats-export.asciidoc

@@ -0,0 +1,18 @@
+[role="xpack"]
+[[stats-export]]
+== Collecting Data from Particular Indices
+
+By default, the monitoring agent collects data from all {es} indices.
+To collect data from particular indices, configure the
+`xpack.monitoring.collection.indices` setting in `elasticsearch.yml`.
+You can specify multiple indices as a comma-separated list or
+use an index pattern to match multiple indices:
+
+[source,yaml]
+----------------------------------
+xpack.monitoring.collection.indices: logstash-*, index1, test2
+----------------------------------
+
+You can prepend `+` or `-` to explicitly include or exclude index
+names or patterns. For example, to include all indices that
+start with `test` except `test3`, you could specify `+test*,-test3`.

docs/en/monitoring/tribe.asciidoc

@@ -0,0 +1,40 @@
+[role="xpack"]
+[[monitoring-tribe]]
+== Configuring a Tribe Node to Work with Monitoring
+
+If you connect to a cluster through a <<modules-tribe,tribe node>>,
+and you want to monitor the tribe node, then you will need to install {xpack} on
+that node as well.
+
+With this configuration, the tribe node is included in the node count displayed
+in the Monitoring UI, but is not included in the node list because it does not
+export any data to the monitoring cluster.
+
+To include the tribe node in the monitoring data, enable Monitoring data
+collection at the tribe level:
+
+[source,yaml]
+----------------------------------
+node.name: my-tribe-node1
+
+tribe:
+  on_conflict: prefer_cluster1
+  c1:
+    cluster.name: cluster1
+    discovery.zen.ping.unicast.hosts: [ "cluster1-node1:9300", "cluster1-node2:9300", "cluster1-node2:9300" ]
+    xpack.monitoring.enabled: true <1>
+  c2:
+    cluster.name: cluster2
+    discovery.zen.ping.unicast.hosts: [ "cluster2-node3:9300", "cluster2-node3:9300", "cluster2-node3:9300" ]
+    xpack.monitoring: <2>
+      enabled: true
+      exporters:
+        id1:
+          type: http
+          host: [ "monitoring-cluster:9200" ]
+----------------------------------
+<1> Enable data collection from the tribe node using a Local Exporter.
+<2> Enable data collection from the tribe node using an HTTP Exporter.
+
+When you enable data collection from the tribe node, it is included in both the
+node count and node list.