Introduce preboot lifecycle stage (#103636)

# Conflicts:
#	.github/CODEOWNERS
#	src/core/server/ui_settings/ui_settings_service.ts

docs/development/core/server/kibana-plugin-core-server.corepreboot.elasticsearch.md

@@ -0,0 +1,13 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [kibana-plugin-core-server](./kibana-plugin-core-server.md) &gt; [CorePreboot](./kibana-plugin-core-server.corepreboot.md) &gt; [elasticsearch](./kibana-plugin-core-server.corepreboot.elasticsearch.md)
+
+## CorePreboot.elasticsearch property
+
+[ElasticsearchServicePreboot](./kibana-plugin-core-server.elasticsearchservicepreboot.md)
+
+<b>Signature:</b>
+
+```typescript
+elasticsearch: ElasticsearchServicePreboot;
+```

docs/development/core/server/kibana-plugin-core-server.corepreboot.http.md

@@ -0,0 +1,13 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [kibana-plugin-core-server](./kibana-plugin-core-server.md) &gt; [CorePreboot](./kibana-plugin-core-server.corepreboot.md) &gt; [http](./kibana-plugin-core-server.corepreboot.http.md)
+
+## CorePreboot.http property
+
+[HttpServicePreboot](./kibana-plugin-core-server.httpservicepreboot.md)
+
+<b>Signature:</b>
+
+```typescript
+http: HttpServicePreboot;
+```

docs/development/core/server/kibana-plugin-core-server.corepreboot.md

@@ -0,0 +1,22 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [kibana-plugin-core-server](./kibana-plugin-core-server.md) &gt; [CorePreboot](./kibana-plugin-core-server.corepreboot.md)
+
+## CorePreboot interface
+
+Context passed to the `setup` method of `preboot` plugins.
+
+<b>Signature:</b>
+
+```typescript
+export interface CorePreboot 
+```
+
+## Properties
+
+|  Property | Type | Description |
+|  --- | --- | --- |
+|  [elasticsearch](./kibana-plugin-core-server.corepreboot.elasticsearch.md) | <code>ElasticsearchServicePreboot</code> | [ElasticsearchServicePreboot](./kibana-plugin-core-server.elasticsearchservicepreboot.md) |
+|  [http](./kibana-plugin-core-server.corepreboot.http.md) | <code>HttpServicePreboot</code> | [HttpServicePreboot](./kibana-plugin-core-server.httpservicepreboot.md) |
+|  [preboot](./kibana-plugin-core-server.corepreboot.preboot.md) | <code>PrebootServicePreboot</code> | [PrebootServicePreboot](./kibana-plugin-core-server.prebootservicepreboot.md) |
+

docs/development/core/server/kibana-plugin-core-server.corepreboot.preboot.md

@@ -0,0 +1,13 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [kibana-plugin-core-server](./kibana-plugin-core-server.md) &gt; [CorePreboot](./kibana-plugin-core-server.corepreboot.md) &gt; [preboot](./kibana-plugin-core-server.corepreboot.preboot.md)
+
+## CorePreboot.preboot property
+
+[PrebootServicePreboot](./kibana-plugin-core-server.prebootservicepreboot.md)
+
+<b>Signature:</b>
+
+```typescript
+preboot: PrebootServicePreboot;
+```

docs/development/core/server/kibana-plugin-core-server.coresetup.md

@@ -4,7 +4,7 @@
 
 ## CoreSetup interface
 
-Context passed to the plugins `setup` method.
+Context passed to the `setup` method of `standard` plugins.
 
 <b>Signature:</b>
 

docs/development/core/server/kibana-plugin-core-server.discoveredplugin.md

@@ -21,4 +21,5 @@ export interface DiscoveredPlugin
 |  [optionalPlugins](./kibana-plugin-core-server.discoveredplugin.optionalplugins.md) | <code>readonly PluginName[]</code> | An optional list of the other plugins that if installed and enabled \*\*may be\*\* leveraged by this plugin for some additional functionality but otherwise are not required for this plugin to work properly. |
 |  [requiredBundles](./kibana-plugin-core-server.discoveredplugin.requiredbundles.md) | <code>readonly PluginName[]</code> | List of plugin ids that this plugin's UI code imports modules from that are not in <code>requiredPlugins</code>. |
 |  [requiredPlugins](./kibana-plugin-core-server.discoveredplugin.requiredplugins.md) | <code>readonly PluginName[]</code> | An optional list of the other plugins that \*\*must be\*\* installed and enabled for this plugin to function properly. |
+|  [type](./kibana-plugin-core-server.discoveredplugin.type.md) | <code>PluginType</code> | Type of the plugin, defaults to <code>standard</code>. |
 

docs/development/core/server/kibana-plugin-core-server.discoveredplugin.type.md

@@ -0,0 +1,13 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [kibana-plugin-core-server](./kibana-plugin-core-server.md) &gt; [DiscoveredPlugin](./kibana-plugin-core-server.discoveredplugin.md) &gt; [type](./kibana-plugin-core-server.discoveredplugin.type.md)
+
+## DiscoveredPlugin.type property
+
+Type of the plugin, defaults to `standard`<!-- -->.
+
+<b>Signature:</b>
+
+```typescript
+readonly type: PluginType;
+```

docs/development/core/server/kibana-plugin-core-server.elasticsearchconfigpreboot.credentialsspecified.md

@@ -0,0 +1,13 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [kibana-plugin-core-server](./kibana-plugin-core-server.md) &gt; [ElasticsearchConfigPreboot](./kibana-plugin-core-server.elasticsearchconfigpreboot.md) &gt; [credentialsSpecified](./kibana-plugin-core-server.elasticsearchconfigpreboot.credentialsspecified.md)
+
+## ElasticsearchConfigPreboot.credentialsSpecified property
+
+Indicates whether Elasticsearch configuration includes credentials (`username`<!-- -->, `password` or `serviceAccountToken`<!-- -->).
+
+<b>Signature:</b>
+
+```typescript
+readonly credentialsSpecified: boolean;
+```

docs/development/core/server/kibana-plugin-core-server.elasticsearchconfigpreboot.hosts.md

@@ -0,0 +1,13 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [kibana-plugin-core-server](./kibana-plugin-core-server.md) &gt; [ElasticsearchConfigPreboot](./kibana-plugin-core-server.elasticsearchconfigpreboot.md) &gt; [hosts](./kibana-plugin-core-server.elasticsearchconfigpreboot.hosts.md)
+
+## ElasticsearchConfigPreboot.hosts property
+
+Hosts that the client will connect to. If sniffing is enabled, this list will be used as seeds to discover the rest of your cluster.
+
+<b>Signature:</b>
+
+```typescript
+readonly hosts: string[];
+```

docs/development/core/server/kibana-plugin-core-server.elasticsearchconfigpreboot.md

@@ -0,0 +1,21 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [kibana-plugin-core-server](./kibana-plugin-core-server.md) &gt; [ElasticsearchConfigPreboot](./kibana-plugin-core-server.elasticsearchconfigpreboot.md)
+
+## ElasticsearchConfigPreboot interface
+
+A limited set of Elasticsearch configuration entries exposed to the `preboot` plugins at `setup`<!-- -->.
+
+<b>Signature:</b>
+
+```typescript
+export interface ElasticsearchConfigPreboot 
+```
+
+## Properties
+
+|  Property | Type | Description |
+|  --- | --- | --- |
+|  [credentialsSpecified](./kibana-plugin-core-server.elasticsearchconfigpreboot.credentialsspecified.md) | <code>boolean</code> | Indicates whether Elasticsearch configuration includes credentials (<code>username</code>, <code>password</code> or <code>serviceAccountToken</code>). |
+|  [hosts](./kibana-plugin-core-server.elasticsearchconfigpreboot.hosts.md) | <code>string[]</code> | Hosts that the client will connect to. If sniffing is enabled, this list will be used as seeds to discover the rest of your cluster. |
+

docs/development/core/server/kibana-plugin-core-server.elasticsearchservicepreboot.config.md

@@ -0,0 +1,22 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [kibana-plugin-core-server](./kibana-plugin-core-server.md) &gt; [ElasticsearchServicePreboot](./kibana-plugin-core-server.elasticsearchservicepreboot.md) &gt; [config](./kibana-plugin-core-server.elasticsearchservicepreboot.config.md)
+
+## ElasticsearchServicePreboot.config property
+
+A limited set of Elasticsearch configuration entries.
+
+<b>Signature:</b>
+
+```typescript
+readonly config: Readonly<ElasticsearchConfigPreboot>;
+```
+
+## Example
+
+
+```js
+const { hosts, credentialsSpecified } = core.elasticsearch.config;
+
+```
+

docs/development/core/server/kibana-plugin-core-server.elasticsearchservicepreboot.createclient.md

@@ -0,0 +1,23 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [kibana-plugin-core-server](./kibana-plugin-core-server.md) &gt; [ElasticsearchServicePreboot](./kibana-plugin-core-server.elasticsearchservicepreboot.md) &gt; [createClient](./kibana-plugin-core-server.elasticsearchservicepreboot.createclient.md)
+
+## ElasticsearchServicePreboot.createClient property
+
+Create application specific Elasticsearch cluster API client with customized config. See [IClusterClient](./kibana-plugin-core-server.iclusterclient.md)<!-- -->.
+
+<b>Signature:</b>
+
+```typescript
+readonly createClient: (type: string, clientConfig?: Partial<ElasticsearchClientConfig>) => ICustomClusterClient;
+```
+
+## Example
+
+
+```js
+const client = elasticsearch.createClient('my-app-name', config);
+const data = await client.asInternalUser.search();
+
+```
+

docs/development/core/server/kibana-plugin-core-server.elasticsearchservicepreboot.md

@@ -0,0 +1,20 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [kibana-plugin-core-server](./kibana-plugin-core-server.md) &gt; [ElasticsearchServicePreboot](./kibana-plugin-core-server.elasticsearchservicepreboot.md)
+
+## ElasticsearchServicePreboot interface
+
+
+<b>Signature:</b>
+
+```typescript
+export interface ElasticsearchServicePreboot 
+```
+
+## Properties
+
+|  Property | Type | Description |
+|  --- | --- | --- |
+|  [config](./kibana-plugin-core-server.elasticsearchservicepreboot.config.md) | <code>Readonly&lt;ElasticsearchConfigPreboot&gt;</code> | A limited set of Elasticsearch configuration entries. |
+|  [createClient](./kibana-plugin-core-server.elasticsearchservicepreboot.createclient.md) | <code>(type: string, clientConfig?: Partial&lt;ElasticsearchClientConfig&gt;) =&gt; ICustomClusterClient</code> | Create application specific Elasticsearch cluster API client with customized config. See [IClusterClient](./kibana-plugin-core-server.iclusterclient.md)<!-- -->. |
+

docs/development/core/server/kibana-plugin-core-server.httpservicepreboot.basepath.md

@@ -0,0 +1,13 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [kibana-plugin-core-server](./kibana-plugin-core-server.md) &gt; [HttpServicePreboot](./kibana-plugin-core-server.httpservicepreboot.md) &gt; [basePath](./kibana-plugin-core-server.httpservicepreboot.basepath.md)
+
+## HttpServicePreboot.basePath property
+
+Access or manipulate the Kibana base path See [IBasePath](./kibana-plugin-core-server.ibasepath.md)<!-- -->.
+
+<b>Signature:</b>
+
+```typescript
+basePath: IBasePath;
+```

docs/development/core/server/kibana-plugin-core-server.httpservicepreboot.md

@@ -0,0 +1,82 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [kibana-plugin-core-server](./kibana-plugin-core-server.md) &gt; [HttpServicePreboot](./kibana-plugin-core-server.httpservicepreboot.md)
+
+## HttpServicePreboot interface
+
+Kibana HTTP Service provides an abstraction to work with the HTTP stack at the `preboot` stage. This functionality allows Kibana to serve user requests even before Kibana becomes fully operational. Only Core and `preboot` plugins can define HTTP routes at this stage.
+
+<b>Signature:</b>
+
+```typescript
+export interface HttpServicePreboot 
+```
+
+## Example
+
+To handle an incoming request in your preboot plugin you should: - Use `@kbn/config-schema` package to create a schema to validate the request `params`<!-- -->, `query`<!-- -->, and `body`<!-- -->. Every incoming request will be validated against the created schema. If validation failed, the request is rejected with `400` status and `Bad request` error without calling the route's handler. To opt out of validating the request, specify `false`<!-- -->.
+
+```ts
+import { schema, TypeOf } from '@kbn/config-schema';
+const validate = {
+  params: schema.object({
+    id: schema.string(),
+  }),
+};
+
+```
+- Declare a function to respond to incoming request. The function will receive `request` object containing request details: url, headers, matched route, as well as validated `params`<!-- -->, `query`<!-- -->, `body`<!-- -->. And `response` object instructing HTTP server to create HTTP response with information sent back to the client as the response body, headers, and HTTP status. Any exception raised during the handler call will generate `500 Server error` response and log error details for further investigation. See below for returning custom error responses.
+
+```ts
+const handler = async (context: RequestHandlerContext, request: KibanaRequest, response: ResponseFactory) => {
+  const data = await findObject(request.params.id);
+  // creates a command to respond with 'not found' error
+  if (!data) {
+    return response.notFound();
+  }
+  // creates a command to send found data to the client and set response headers
+  return response.ok({
+    body: data,
+    headers: { 'content-type': 'application/json' }
+  });
+}
+
+```
+\* - Acquire `preboot` [IRouter](./kibana-plugin-core-server.irouter.md) instance and register route handler for GET request to 'path/<!-- -->{<!-- -->id<!-- -->}<!-- -->' path.
+
+```ts
+import { schema, TypeOf } from '@kbn/config-schema';
+
+const validate = {
+  params: schema.object({
+    id: schema.string(),
+  }),
+};
+
+httpPreboot.registerRoutes('my-plugin', (router) => {
+  router.get({ path: 'path/{id}', validate }, async (context, request, response) => {
+    const data = await findObject(request.params.id);
+    if (!data) {
+      return response.notFound();
+    }
+    return response.ok({
+      body: data,
+      headers: { 'content-type': 'application/json' }
+    });
+  });
+});
+
+```
+
+## Properties
+
+|  Property | Type | Description |
+|  --- | --- | --- |
+|  [basePath](./kibana-plugin-core-server.httpservicepreboot.basepath.md) | <code>IBasePath</code> | Access or manipulate the Kibana base path See [IBasePath](./kibana-plugin-core-server.ibasepath.md)<!-- -->. |
+
+## Methods
+
+|  Method | Description |
+|  --- | --- |
+|  [registerRoutes(path, callback)](./kibana-plugin-core-server.httpservicepreboot.registerroutes.md) | Provides ability to acquire <code>preboot</code> [IRouter](./kibana-plugin-core-server.irouter.md) instance for a particular top-level path and register handler functions for any number of nested routes. |
+

docs/development/core/server/kibana-plugin-core-server.httpservicepreboot.registerroutes.md

@@ -0,0 +1,40 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [kibana-plugin-core-server](./kibana-plugin-core-server.md) &gt; [HttpServicePreboot](./kibana-plugin-core-server.httpservicepreboot.md) &gt; [registerRoutes](./kibana-plugin-core-server.httpservicepreboot.registerroutes.md)
+
+## HttpServicePreboot.registerRoutes() method
+
+Provides ability to acquire `preboot` [IRouter](./kibana-plugin-core-server.irouter.md) instance for a particular top-level path and register handler functions for any number of nested routes.
+
+<b>Signature:</b>
+
+```typescript
+registerRoutes(path: string, callback: (router: IRouter) => void): void;
+```
+
+## Parameters
+
+|  Parameter | Type | Description |
+|  --- | --- | --- |
+|  path | <code>string</code> |  |
+|  callback | <code>(router: IRouter) =&gt; void</code> |  |
+
+<b>Returns:</b>
+
+`void`
+
+## Remarks
+
+Each route can have only one handler function, which is executed when the route is matched. See the [IRouter](./kibana-plugin-core-server.irouter.md) documentation for more information.
+
+## Example
+
+
+```ts
+registerRoutes('my-plugin', (router) => {
+  // handler is called when '/my-plugin/path' resource is requested with `GET` method
+  router.get({ path: '/path', validate: false }, (context, req, res) => res.ok({ content: 'ok' }));
+});
+
+```
+