[7.x][DOCS] Adds Configuration section to Node.JS docs (#1396)

Author: szabosteve

docs/advanced-config.asciidoc

@@ -0,0 +1,120 @@
+[[advanced-config]]
+=== Advanced configuration
+
+If you need to customize the client behavior heavily, you are in the right 
+place! The client enables you to customize the following internals:
+
+* `Transport` class
+* `ConnectionPool` class
+* `Connection` class
+* `Serializer` class
+
+
+[discrete]
+==== `Transport`
+
+This class is responsible for performing the request to {es} and handling 
+errors, it also handles the sniffing.
+
+[source,js]
+----
+const { Client, Transport } = require('@elastic/elasticsearch')
+
+class MyTransport extends Transport {
+  request (params, options, callback) {
+    // your code
+  }
+}
+
+const client = new Client({
+    Transport: MyTransport
+})
+----
+
+Sometimes you need to inject a small snippet of your code and then continue to 
+use the usual client code. In such cases, call `super.method`:
+
+[source,js]
+----
+class MyTransport extends Transport {
+  request (params, options, callback) {
+    // your code
+    return super.request(params, options, callback)
+  }
+}
+----
+
+
+[discrete]
+==== `ConnectionPool`
+
+This class is responsible for keeping in memory all the {es} Connection that you 
+are using. There is a single Connection for every node. The connection pool 
+handles the resurrection strategies and the updates of the pool.
+
+[source,js]
+----
+const { Client, ConnectionPool } = require('@elastic/elasticsearch')
+
+class MyConnectionPool extends ConnectionPool {
+  markAlive (connection) {
+    // your code
+    super.markAlive(connection)
+  }
+}
+
+const client = new Client({
+    ConnectionPool: MyConnectionPool
+})
+----
+
+
+[discrete]
+==== `Connection`
+
+This class represents a single node, it holds every information we have on the 
+node, such as roles, id, URL, custom headers and so on. The actual HTTP request 
+is performed here, this means that if you want to swap the default HTTP client 
+(Node.js core), you should override the `request` method of this class.
+
+[source,js]
+----
+const { Client, Connection } = require('@elastic/elasticsearch')
+
+class MyConnection extends Connection {
+  request (params, callback) {
+    // your code
+  }
+}
+
+const client = new Client({
+  Connection: MyConnection
+})
+----
+
+
+[discrete]
+==== `Serializer`
+
+This class is responsible for the serialization of every request, it offers the 
+following methods:
+
+* `serialize(object: any): string;` serializes request objects.
+* `deserialize(json: string): any;` deserializes response strings.
+* `ndserialize(array: any[]): string;` serializes bulk request objects.
+* `qserialize(object: any): string;` serializes request query parameters.
+
+[source,js]
+----
+const { Client, Serializer } = require('@elastic/elasticsearch')
+
+class MySerializer extends Serializer {
+  serialize (object) {
+    // your code
+  }
+}
+
+const client = new Client({
+  Serializer: MySerializer
+})
+----

docs/basic-config.asciidoc

@@ -0,0 +1,247 @@
+[[basic-config]]
+=== Basic configuration
+
+This page shows you the possible basic configuration options that the clients 
+offers.
+
+
+[source,js]
+----
+const { Client } = require('@elastic/elasticsearch')
+
+const client = new Client({
+  node: 'http://localhost:9200',
+  maxRetries: 5,
+  requestTimeout: 60000,
+  sniffOnStart: true
+})
+----
+
+
+[cols=2*]
+|===
+|`node` or `nodes`
+a|The Elasticsearch endpoint to use. +
+It can be a single string or an array of strings:
+[source,js]
+----
+node: 'http://localhost:9200'
+----
+Or it can be an object (or an array of objects) that represents the node:
+[source,js]
+----
+node: {
+  url: new URL('http://localhost:9200'),
+  ssl: 'ssl options',
+  agent: 'http agent options',
+  id: 'custom node id',
+  headers: { 'custom': 'headers' }
+  roles: {
+    master: true,
+    data: true,
+    ingest: true,
+    ml: false
+  }
+}
+----
+
+|`auth`
+a|Your authentication data. You can use both basic authentication and 
+{ref}/security-api-create-api-key.html[ApiKey]. +
+See https://www.elastic.co/guide/en/elasticsearch/client/javascript-api/current/auth-reference.html[Authentication] 
+for more details. +
+_Default:_ `null`
+
+Basic authentication:
+[source,js]
+----
+auth: {
+  username: 'elastic',
+  password: 'changeme'
+}
+----
+{ref}/security-api-create-api-key.html[ApiKey] authentication:
+[source,js]
+----
+auth: {
+  apiKey: 'base64EncodedKey'
+}
+----
+
+
+|`maxRetries`
+|`number` - Max number of retries for each request. +
+_Default:_ `3`
+
+|`requestTimeout`
+|`number` - Max request timeout in milliseconds for each request. +
+_Default:_ `30000`
+
+|`pingTimeout`
+|`number` - Max ping request timeout in milliseconds for each request. +
+_Default:_ `3000`
+
+|`sniffInterval`
+|`number, boolean` - Perform a sniff operation every `n` milliseconds. Sniffing might not be the best solution for you, take a look https://www.elastic.co/blog/elasticsearch-sniffing-best-practices-what-when-why-how[here] to know more. +
+_Default:_ `false`
+
+|`sniffOnStart`
+|`boolean` - Perform a sniff once the client is started. Sniffing might not be the best solution for you, take a look https://www.elastic.co/blog/elasticsearch-sniffing-best-practices-what-when-why-how[here] to know more. +
+_Default:_ `false`
+
+|`sniffEndpoint`
+|`string` - Endpoint to ping during a sniff. +
+_Default:_ `'_nodes/_all/http'`
+
+|`sniffOnConnectionFault`
+|`boolean` - Perform a sniff on connection fault. Sniffing might not be the best solution for you, take a look https://www.elastic.co/blog/elasticsearch-sniffing-best-practices-what-when-why-how[here] to know more. +
+_Default:_ `false`
+
+|`resurrectStrategy`
+|`string` - Configure the node resurrection strategy. +
+_Options:_ `'ping'`, `'optimistic'`, `'none'` +
+_Default:_ `'ping'`
+
+|`suggestCompression`
+|`boolean` - Adds `accept-encoding` header to every request. +
+_Default:_ `false`
+
+|`compression`
+|`string, boolean` - Enables gzip request body compression. +
+_Options:_ `'gzip'`, `false` +
+_Default:_ `false`
+
+|`ssl`
+|`http.SecureContextOptions` - ssl https://nodejs.org/api/tls.html[configuraton]. +
+_Default:_ `null`
+
+|`proxy`
+a|`string, URL` - If you are using an http(s) proxy, you can put its url here.
+The client will automatically handle the connection to it. +
+_Default:_ `null`
+[source,js]
+----
+const client = new Client({
+  node: 'http://localhost:9200',
+  proxy: 'http://localhost:8080'
+})
+
+// Proxy with basic authentication
+const client = new Client({
+  node: 'http://localhost:9200',
+  proxy: 'http://user:pwd@localhost:8080'
+})
+----
+
+|`agent`
+a|`http.AgentOptions, function` - http agent https://nodejs.org/api/http.html#http_new_agent_options[options], 
+or a function that returns an actual http agent instance. If you want to disable the http agent use entirely
+(and disable the `keep-alive` feature), set the agent to `false`. +
+_Default:_ `null`
+[source,js]
+----
+const client = new Client({
+  node: 'http://localhost:9200',
+  agent: { agent: 'options' }
+})
+
+const client = new Client({
+  node: 'http://localhost:9200',
+  // the function takes as parameter the option
+  // object passed to the Connection constructor
+  agent: (opts) => new CustomAgent()
+})
+
+const client = new Client({
+  node: 'http://localhost:9200',
+  // Disable agent and keep-alive
+  agent: false
+})
+----
+
+|`nodeFilter`
+a|`function` - Filters which node not to use for a request. +
+_Default:_
+[source,js]
+----
+function defaultNodeFilter (node) {
+  // avoid master only nodes
+  if (node.roles.master === true &&
+      node.roles.data === false &&
+      node.roles.ingest === false) {
+    return false
+  }
+  return true
+}
+----
+
+|`nodeSelector`
+a|`function` - custom selection strategy. +
+_Options:_ `'round-robin'`, `'random'`, custom function +
+_Default:_ `'round-robin'` +
+_Custom function example:_
+[source,js]
+----
+function nodeSelector (connections) {
+  const index = calculateIndex()
+  return connections[index]
+}
+----
+
+|`generateRequestId`
+a|`function` - function to generate the request id for every request, it takes 
+two parameters, the request parameters and options. +
+By default it generates an incremental integer for every request. +
+_Custom function example:_
+[source,js]
+----
+function generateRequestId (params, options) {
+  // your id generation logic
+  // must be syncronous
+  return 'id'
+}
+----
+
+|`name`
+|`string, symbol` - The name to identify the client instance in the events. +
+_Default:_ `elasticsearch-js`
+
+|`opaqueIdPrefix`
+|`string` - A string that will be use to prefix any `X-Opaque-Id` header. +
+See https://www.elastic.co/guide/en/elasticsearch/client/javascript-api/current/observability.html#_x-opaque-id_support[`X-Opaque-Id` support] for more details. +
+_Default:_ `null`
+
+|`headers`
+|`object` - A set of custom headers to send in every request. +
+_Default:_ `{}`
+
+|`context`
+|`object` - A custom object that you can use for observability in your events.
+It will be merged with the API level context option. +
+_Default:_ `null`
+
+|`enableMetaHeader`
+|`boolean` - If true, adds an header named `'x-elastic-client-meta'`, containing some minimal telemetry data,
+such as the client and platform version. +
+_Default:_ `true`
+
+|`cloud`
+a|`object` - Custom configuration for connecting to 
+https://cloud.elastic.co[Elastic Cloud]. See https://www.elastic.co/guide/en/elasticsearch/client/javascript-api/current/auth-reference.html[Authentication] 
+for more details. +
+_Default:_ `null` + 
+_Cloud configuration example:_ 
+[source,js]
+----
+const client = new Client({
+  cloud: {
+    id: 'name:bG9jYWxob3N0JGFiY2QkZWZnaA=='
+  }, 
+  auth: {
+    username: 'elastic',
+    password: 'changeme'
+  }
+})
+----
+
+|===

docs/child.asciidoc

@@ -1,5 +1,5 @@
-[[child-client]]
-== Creating a child client
+[[child]]
+=== Creating a child client
 
 There are some use cases where you may need multiple instances of the client. 
 You can easily do that by calling `new Client()` as many times as you need, but