[docs] Init es client section

docs/development/plugin-development.asciidoc

@@ -8,6 +8,8 @@ The Kibana plugin interfaces are in a state of constant development.  We cannot
 
 * <<development-plugin-resources>>
 * <<development-uiexports>>
+* <<development-elasticsearch>>
+
 
 include::plugin/development-plugin-resources.asciidoc[]
 

docs/development/plugin/development-elasticsearch.asciidoc

@@ -1,4 +1,41 @@
 [[development-elasticsearch]]
 === Communicating with elasticsearch
 
-Kibana exposes clients for communicating with elasticsearch on the server passed into each plugin.
+Kibana exposes two clients on the server and browser for communicating with elasticsearch.
+There is an 'admin' client which is used for managing Kibana's state, and a 'data' client for all
+other requests.  The clients use the elasticsearch.js library.
+
+[float]
+[[client-server]]
+=== Server clients
+
+Server clients are exposed through the elasticsearch plugin.
+[source,javascript]
+----
+  const adminCluster = server.plugins.elasticsearch.getCluster('admin);
+  const dataCluster = server.plugins.elasticsearch.getCluster('data);
+
+  //ping as the configured elasticsearch.user in kibana.yml
+  adminCluster.callWithInternalUser('ping');
+
+  //ping as the user specified in the current requests header
+  adminCluster.callWithRequest(req, 'ping');
+----
+
+[float]
+[[client-browser]]
+=== Browser clients
+
+Browser clients are exposed through AngularJS services.
+
+[source,javascript]
+----
+uiModules.get('kibana')
+.run(function (esAdmin, es) {
+  es.ping()
+  .then(() => esAdmin.ping())
+  .catch(err => {
+    console.log('error pinging servers);
+  });
+});
+----

docs/setup/tribe.asciidoc

@@ -23,7 +23,7 @@ The full list of configurations can be found at <<settings>>.
 [[tribe-limitations]]
 === Limitations
 
-Due to the ambiguity of which cluster is being used, certain features are disabled in Kibana: 
+Due to the ambiguity of which cluster is being used, certain features are disabled in Kibana:
 
 * Console
 * Managing users and roles with the x-pack plugin