kibana/docs/developer/architecture/core/index.asciidoc

[[kibana-platform-api]]
== {kib} Core API

experimental[]

{kib} Core provides a set of low-level API's required to run all {kib} plugins.
These API's are injected into your plugin's lifecycle methods and may be invoked during that lifecycle only:

[source,typescript]
----
import type { PluginInitializerContext, CoreSetup, CoreStart } from 'kibana/server';

export class MyPlugin {
  constructor(initializerContext: PluginInitializerContext) {}

  public setup(core: CoreSetup) {
    // called when plugin is setting up during Kibana's startup sequence
  }

  public start(core: CoreStart) {
    // called after all plugins are set up
  }

  public stop() {
    // called when plugin is torn down during Kibana's shutdown sequence
  }
}
----

=== Server-side
[[configuration-service]]
==== Configuration service
{kib} provides `ConfigService` if a plugin developer may want to support
adjustable runtime behavior for their plugins.
Plugins can only read their own configuration values, it is not possible to access the configuration values from {kib} Core or other plugins directly.

[source,js]
----
// in Legacy platform
const basePath = config.get('server.basePath');
// in Kibana Platform 'basePath' belongs to the http service
const basePath = core.http.basePath.get(request);
----

To have access to your plugin config, you _should_:

* Declare plugin-specific `configPath` (will fallback to plugin `id`
if not specified) in {kib-repo}blob/{branch}/docs/development/core/server/kibana-plugin-core-server.pluginmanifest.md[`kibana.json`] manifest file.
* Export schema validation for the config from plugin's main file. Schema is
mandatory. If a plugin reads from the config without schema declaration,
`ConfigService` will throw an error.

*my_plugin/server/index.ts*
[source,typescript]
----
import { schema, TypeOf } from '@kbn/config-schema';
export const plugin = …
export const config = {
  schema: schema.object(…),
};
export type MyPluginConfigType = TypeOf<typeof config.schema>;
----

* Read config value exposed via `PluginInitializerContext`.
*my_plugin/server/index.ts*
[source,typescript]
----
import type { PluginInitializerContext } from 'kibana/server';
export class MyPlugin {
  constructor(initializerContext: PluginInitializerContext) {
    this.config$ = initializerContext.config.create<MyPluginConfigType>();
    // or if config is optional:
    this.config$ = initializerContext.config.createIfExists<MyPluginConfigType>();
  }
----

If your plugin also has a client-side part, you can also expose
configuration properties to it using the configuration `exposeToBrowser`
allow-list property.

*my_plugin/server/index.ts*
[source,typescript]
----
import { schema, TypeOf } from '@kbn/config-schema';
import type { PluginConfigDescriptor } from 'kibana/server';

const configSchema = schema.object({
  secret: schema.string({ defaultValue: 'Only on server' }),
  uiProp: schema.string({ defaultValue: 'Accessible from client' }),
});

type ConfigType = TypeOf<typeof configSchema>;

export const config: PluginConfigDescriptor<ConfigType> = {
  exposeToBrowser: {
    uiProp: true,
  },
  schema: configSchema,
};
----

Configuration containing only the exposed properties will be then
available on the client-side using the plugin's `initializerContext`:

*my_plugin/public/index.ts*
[source,typescript]
----
interface ClientConfigType {
  uiProp: string;
}

export class MyPlugin implements Plugin<PluginSetup, PluginStart> {
  constructor(private readonly initializerContext: PluginInitializerContext) {}

  public async setup(core: CoreSetup, deps: {}) {
    const config = this.initializerContext.config.get<ClientConfigType>();
  }
----

All plugins are considered enabled by default. If you want to disable
your plugin, you could declare the `enabled` flag in the plugin
config. This is a special {kib} Platform key. {kib} reads its
value and won’t create a plugin instance if `enabled: false`.

[source,js]
----
export const config = {
  schema: schema.object({ enabled: schema.boolean({ defaultValue: false }) }),
};
----
[[handle-plugin-configuration-deprecations]]
===== Handle plugin configuration deprecations
If your plugin has deprecated configuration keys, you can describe them using
the `deprecations` config descriptor field.
Deprecations are managed on a per-plugin basis, meaning you don’t need to specify
the whole property path, but use the relative path from your plugin’s
configuration root.

*my_plugin/server/index.ts*
[source,typescript]
----
import { schema, TypeOf } from '@kbn/config-schema';
import type { PluginConfigDescriptor } from 'kibana/server';

const configSchema = schema.object({
  newProperty: schema.string({ defaultValue: 'Some string' }),
});

type ConfigType = TypeOf<typeof configSchema>;

export const config: PluginConfigDescriptor<ConfigType> = {
  schema: configSchema,
  deprecations: ({ rename, unused }) => [
    rename('oldProperty', 'newProperty'),
    unused('someUnusedProperty'),
  ],
};
----

In some cases, accessing the whole configuration for deprecations is
necessary. For these edge cases, `renameFromRoot` and `unusedFromRoot`
are also accessible when declaring deprecations.

*my_plugin/server/index.ts*
[source,typescript]
----
export const config: PluginConfigDescriptor<ConfigType> = {
  schema: configSchema,
  deprecations: ({ renameFromRoot, unusedFromRoot }) => [
    renameFromRoot('oldplugin.property', 'myplugin.property'),
    unusedFromRoot('oldplugin.deprecated'),
  ],
};
----
==== Logging service
Allows a plugin to provide status and diagnostic information.
For detailed instructions see the {kib-repo}blob/{branch}/src/core/server/logging/README.md[logging service documentation].

[source,typescript]
----
import type { PluginInitializerContext, CoreSetup, Plugin, Logger } from 'kibana/server';

export class MyPlugin implements Plugin {
  private readonly logger: Logger;

  constructor(initializerContext: PluginInitializerContext) {
    this.logger = initializerContext.logger.get();
  }

  public setup(core: CoreSetup) {
    try {
      this.logger.debug('doing something...');
      // …
    } catch (e) {
      this.logger.error('failed doing something...');
    }
  }
}
----

==== Elasticsearch service
`Elasticsearch service` provides `elasticsearch.client` program API to communicate with Elasticsearch server REST API.
`elasticsearch.client` interacts with Elasticsearch service on behalf of:

- `kibana_system` user via `elasticsearch.client.asInternalUser.*` methods.
- a current end-user via `elasticsearch.client.asCurrentUser.*` methods. In this case Elasticsearch client should be given the current user credentials.
See <<scoped-services>> and <<development-security>>.

{kib-repo}blob/{branch}/docs/development/core/server/kibana-plugin-core-server.elasticsearchservicestart.md[Elasticsearch service API docs]

[source,typescript]
----
import { CoreStart, Plugin } from 'kibana/public';

export class MyPlugin implements Plugin {
  public start(core: CoreStart) {
    async function asyncTask() {
      const result = await core.elasticsearch.client.asInternalUser.ping(…);
    }
    asyncTask();
  }
}
----

For advanced use-cases, such as a search, use {kib-repo}blob/{branch}/docs/development/plugins/data/server/kibana-plugin-plugins-data-server.md[Data plugin]

include::saved-objects-service.asciidoc[leveloffset=+1]

==== HTTP service
Allows plugins:

* to extend the {kib} server with custom REST API.
* to execute custom logic on an incoming request or server response.
* implement custom authentication and authorization strategy.

See {kib-repo}blob/{branch}/docs/development/core/server/kibana-plugin-core-server.httpservicesetup.md[HTTP service API docs]

[source,typescript]
----
import { schema } from '@kbn/config-schema';
import type { CoreSetup, Plugin } from 'kibana/server';

export class MyPlugin implements Plugin {
  public setup(core: CoreSetup) {
    const router = core.http.createRouter();
    
    const validate = {
      params: schema.object({
        id: schema.string(),
      }),
    };
    
    router.get({
      path: 'my_plugin/{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'
        }
      });
    });
  }
}
----

==== UI settings service
The program interface to <<advanced-options, UI settings>>.
It makes it possible for Kibana plugins to extend Kibana UI Settings Management with custom settings.

See:

- {kib-repo}blob/{branch}/docs/development/core/server/kibana-plugin-core-server.uisettingsservicesetup.register.md[UI settings service Setup API docs]
- {kib-repo}blob/{branch}/docs/development/core/server/kibana-plugin-core-server.uisettingsservicestart.register.md[UI settings service Start API docs]

[source,typescript]
----
import { schema } from '@kbn/config-schema';
import type { CoreSetup,Plugin } from 'kibana/server';

export class MyPlugin implements Plugin {
  public setup(core: CoreSetup) {
    core.uiSettings.register({
      custom: { 
        value: '42',
        schema: schema.string(),
      },
    });
    const router = core.http.createRouter();
    router.get({
      path: 'my_plugin/{id}',
      validate: …,
    },
    async (context, request, response) => {
      const customSetting = await context.uiSettings.client.get('custom');
      …
    });
  }
}

----

=== Client-side
==== Application service
Kibana has migrated to be a Single Page Application. Plugins should use `Application service` API to instruct Kibana what an application should be loaded & rendered in the UI in response to user interactions.
[source,typescript]
----
import { AppMountParameters, CoreSetup, Plugin, DEFAULT_APP_CATEGORIES } from 'kibana/public';

export class MyPlugin implements Plugin {
  public setup(core: CoreSetup) {
    core.application.register({ // <1>
      category: DEFAULT_APP_CATEGORIES.kibana,
      id: 'my-plugin',
      title: 'my plugin title',
      euiIconType: '/path/to/some.svg',
      order: 100,
      appRoute: '/app/my_plugin', // <2>
      async mount(params: AppMountParameters) { // <3>
        // Load application bundle
        const { renderApp } = await import('./application');
        // Get start services
        const [coreStart, depsStart] = await core.getStartServices(); // <4>
        // Render the application
        return renderApp(coreStart, depsStart, params); // <5>
      },
    });
  }
}
----
<1> See {kib-repo}blob/{branch}/docs/development/core/public/kibana-plugin-core-public.applicationsetup.register.md[application.register interface]
<2> Application specific URL.
<3> `mount` callback is invoked when a user navigates to the application-specific URL.
<4> `core.getStartServices` method provides API available during `start` lifecycle.
<5> `mount` method must return a function that will be called to unmount the application.

NOTE:: you are free to use any UI library to render a plugin application in DOM.
However, we recommend using React and https://elastic.github.io/eui[EUI] for all your basic UI
components to create a consistent UI experience.

==== HTTP service
Provides API to communicate with the {kib} server. Feel free to use another HTTP client library to request 3rd party services.

[source,typescript]
----
import { CoreStart } from 'kibana/public';
interface ResponseType {…};
async function fetchData<ResponseType>(core: CoreStart) {
  return await core.http.get<>(
    '/api/my_plugin/',
    { query: … },
  ); 
}
----
See {kib-repo}blob/{branch}/docs/development/core/public/kibana-plugin-core-public.httpsetup.md[for all available API].

==== Elasticsearch service
Not available in the browser. Use {kib-repo}blob/{branch}/docs/development/plugins/data/public/kibana-plugin-plugins-data-public.md[Data plugin] instead.

== Patterns
[[scoped-services]]
=== Scoped services
Whenever Kibana needs to get access to data saved in elasticsearch, it
should perform a check whether an end-user has access to the data. In
the legacy platform, Kibana requires binding elasticsearch related API
with an incoming request to access elasticsearch service on behalf of a
user.

[source,js]
----
async function handler(req, res) {
  const dataCluster = server.plugins.elasticsearch.getCluster('data');
  const data = await dataCluster.callWithRequest(req, 'ping');
}
----

The Kibana Platform introduced a handler interface on the server-side to perform that association
internally. Core services, that require impersonation with an incoming
request, are exposed via `context` argument of
{kib-repo}blob/{branch}/docs/development/core/server/kibana-plugin-core-server.requesthandler.md[the
request handler interface.] The above example looks in the Kibana Platform
as

[source,js]
----
async function handler(context, req, res) {
  const data = await context.core.elasticsearch.client.asCurrentUser('ping');
}
----

The
{kib-repo}blob/{branch}/docs/development/core/server/kibana-plugin-core-server.requesthandlercontext.md[request
handler context] exposed the next scoped *core* services:

[width="100%",cols="30%,70%",options="header",]
|===
|Legacy Platform |Kibana Platform
|`request.getSavedObjectsClient`
|{kib-repo}blob/{branch}/docs/development/core/server/kibana-plugin-core-server.savedobjectsclient.md[`context.savedObjects.client`]

|`server.plugins.elasticsearch.getCluster('admin')`
|{kib-repo}blob/{branch}/docs/development/core/server/kibana-plugin-core-server.iscopedclusterclient.md[`context.elasticsearch.client`]

|`server.plugins.elasticsearch.getCluster('data')`
|{kib-repo}blob/{branch}/docs/development/core/server/kibana-plugin-core-server.iscopedclusterclient.md[`context.elasticsearch.client`]

|`request.getUiSettingsService`
|{kib-repo}blob/{branch}/docs/development/core/server/kibana-plugin-core-server.iuisettingsclient.md[`context.uiSettings.client`]
|===

==== Declare a custom scoped service

Plugins can extend the handler context with a custom API that will be
available to the plugin itself and all dependent plugins. For example,
the plugin creates a custom elasticsearch client and wants to use it via
the request handler context:

[source,typescript]
----
import type { CoreSetup, IScopedClusterClient } from 'kibana/server';

export interface MyPluginContext {
  client: IScopedClusterClient;
}

// extend RequestHandlerContext when a dependent plugin imports MyPluginContext from the file
declare module 'kibana/server' {
  interface RequestHandlerContext {
    myPlugin?: MyPluginContext;
  }
}

class MyPlugin {
  setup(core: CoreSetup) {
    const client = core.elasticsearch.createClient('myClient');
    core.http.registerRouteHandlerContext('myPlugin', (context, req, res) => {
      return { client: client.asScoped(req) };
    });
    const router = core.http.createRouter();
    router.get(
      { path: '/api/my-plugin/', validate: … },
      async (context, req, res) => {
        const data = await context.myPlugin.client.asCurrentUser('endpoint');
      }
    );
  }
----