[Feature Flags Service] Hello world 👋

.github/CODEOWNERS

@@ -176,6 +176,12 @@ packages/core/execution-context/core-execution-context-server-mocks @elastic/kib
 packages/core/fatal-errors/core-fatal-errors-browser @elastic/kibana-core
 packages/core/fatal-errors/core-fatal-errors-browser-internal @elastic/kibana-core
 packages/core/fatal-errors/core-fatal-errors-browser-mocks @elastic/kibana-core
+packages/core/feature-flags/core-feature-flags-browser @elastic/kibana-core
+packages/core/feature-flags/core-feature-flags-browser-internal @elastic/kibana-core
+packages/core/feature-flags/core-feature-flags-browser-mocks @elastic/kibana-core
+packages/core/feature-flags/core-feature-flags-server @elastic/kibana-core
+packages/core/feature-flags/core-feature-flags-server-internal @elastic/kibana-core
+packages/core/feature-flags/core-feature-flags-server-mocks @elastic/kibana-core
 test/plugin_functional/plugins/core_history_block @elastic/kibana-core
 packages/core/http/core-http-browser @elastic/kibana-core
 packages/core/http/core-http-browser-internal @elastic/kibana-core
@@ -443,6 +449,7 @@ examples/expressions_explorer @elastic/kibana-visualizations
 src/plugins/expressions @elastic/kibana-visualizations
 packages/kbn-failed-test-reporter-cli @elastic/kibana-operations @elastic/appex-qa
 examples/feature_control_examples @elastic/kibana-security
+examples/feature_flags_example @elastic/kibana-core
 x-pack/test/plugin_api_integration/plugins/feature_usage_test @elastic/kibana-security
 x-pack/plugins/features @elastic/kibana-core
 x-pack/test/functional_execution_context/plugins/alerts @elastic/kibana-core

docs/developer/plugin-list.asciidoc

@@ -503,8 +503,8 @@ The plugin exposes the static DefaultEditorController class to consume.
 
 
 |{kib-repo}blob/{branch}/x-pack/plugins/cloud_integrations/cloud_experiments/README.mdx[cloudExperiments]
-|[!WARNING]
-These APIs are deprecated and should not be used as we're working on a replacement Core Feature Flags Service that will arrive soon.
+|[!NOTE]
+This plugin no-longer exposes any evaluation APIs. Refer to <DocLink id="kibFeatureFlagsService" /> for more information about how to interact with feature flags.
 
 
 |{kib-repo}blob/{branch}/x-pack/plugins/cloud_integrations/cloud_full_story/README.md[cloudFullStory]

examples/feature_flags_example/README.md

@@ -0,0 +1,5 @@
+# featureFlagsExample
+
+This plugin's goal is to demonstrate how to use the core feature flags service.
+
+Refer to [the docs](../../packages/core/feature-flags/README.mdx) to know more.

examples/feature_flags_example/common/index.ts

@@ -0,0 +1,10 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+export const PLUGIN_ID = 'featureFlagsExample';
+export const PLUGIN_NAME = 'Feature Flags Example';

examples/feature_flags_example/kibana.jsonc

@@ -0,0 +1,13 @@
+{
+  "type": "plugin",
+  "id": "@kbn/feature-flags-example-plugin",
+  "owner": "@elastic/kibana-core",
+  "description": "Plugin that shows how to make use of the feature flags core service.",
+  "plugin": {
+    "id": "featureFlagsExample",
+    "server": true,
+    "browser": true,
+    "requiredPlugins": ["developerExamples"],
+    "optionalPlugins": []
+  }
+}

examples/feature_flags_example/public/application.tsx

@@ -0,0 +1,32 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+import React from 'react';
+import ReactDOM from 'react-dom';
+import { AppMountParameters, CoreStart } from '@kbn/core/public';
+import { KibanaPageTemplate } from '@kbn/shared-ux-page-kibana-template';
+import { KibanaRootContextProvider } from '@kbn/react-kibana-context-root';
+import { FeatureFlagsExampleApp } from './components/app';
+
+export const renderApp = (coreStart: CoreStart, { element }: AppMountParameters) => {
+  const { notifications, http, featureFlags } = coreStart;
+  ReactDOM.render(
+    <KibanaRootContextProvider {...coreStart}>
+      <KibanaPageTemplate>
+        <FeatureFlagsExampleApp
+          featureFlags={featureFlags}
+          notifications={notifications}
+          http={http}
+        />
+      </KibanaPageTemplate>
+    </KibanaRootContextProvider>,
+    element
+  );
+
+  return () => ReactDOM.unmountComponentAtNode(element);
+};

examples/feature_flags_example/public/components/app.tsx

@@ -0,0 +1,85 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+import React from 'react';
+import {
+  EuiHorizontalRule,
+  EuiPageTemplate,
+  EuiTitle,
+  EuiText,
+  EuiLink,
+  EuiListGroup,
+  EuiListGroupItem,
+} from '@elastic/eui';
+import type { CoreStart, FeatureFlagsStart } from '@kbn/core/public';
+
+import useObservable from 'react-use/lib/useObservable';
+import { PLUGIN_NAME } from '../../common';
+
+interface FeatureFlagsExampleAppDeps {
+  featureFlags: FeatureFlagsStart;
+  notifications: CoreStart['notifications'];
+  http: CoreStart['http'];
+}
+
+export const FeatureFlagsExampleApp = ({ featureFlags }: FeatureFlagsExampleAppDeps) => {
+  // Fetching the feature flags synchronously
+  const bool = featureFlags.getBooleanValue('example-boolean', false);
+  const str = featureFlags.getStringValue('example-string', 'red');
+  const num = featureFlags.getNumberValue('example-number', 1);
+
+  // Use React Hooks to observe feature flags changes
+  const bool$ = useObservable(featureFlags.getBooleanValue$('example-boolean', false));
+  const str$ = useObservable(featureFlags.getStringValue$('example-string', 'red'));
+  const num$ = useObservable(featureFlags.getNumberValue$('example-number', 1));
+
+  return (
+    <>
+      <EuiPageTemplate>
+        <EuiPageTemplate.Header>
+          <EuiTitle size="l">
+            <h1>{PLUGIN_NAME}</h1>
+          </EuiTitle>
+        </EuiPageTemplate.Header>
+        <EuiPageTemplate.Section>
+          <EuiTitle>
+            <h2>Demo of the feature flags service</h2>
+          </EuiTitle>
+          <EuiText>
+            <p>
+              To learn more, refer to{' '}
+              <EuiLink
+                href={'https://docs.elastic.dev/kibana-dev-docs/tutorials/feature-flags-service'}
+              >
+                the docs
+              </EuiLink>
+              .
+            </p>
+            <EuiHorizontalRule />
+            <EuiListGroup>
+              <p>
+                The feature flags are:
+                <EuiListGroupItem label={`example-boolean: ${bool}`} />
+                <EuiListGroupItem label={`example-string: ${str}`} />
+                <EuiListGroupItem label={`example-number: ${num}`} />
+              </p>
+            </EuiListGroup>
+            <EuiListGroup>
+              <p>
+                The <strong>observed</strong> feature flags are:
+                <EuiListGroupItem label={`example-boolean: ${bool$}`} />
+                <EuiListGroupItem label={`example-string: ${str$}`} />
+                <EuiListGroupItem label={`example-number: ${num$}`} />
+              </p>
+            </EuiListGroup>
+          </EuiText>
+        </EuiPageTemplate.Section>
+      </EuiPageTemplate>
+    </>
+  );
+};

examples/feature_flags_example/public/index.ts

@@ -0,0 +1,13 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+import { FeatureFlagsExamplePlugin } from './plugin';
+
+export function plugin() {
+  return new FeatureFlagsExamplePlugin();
+}

examples/feature_flags_example/public/plugin.ts

@@ -0,0 +1,39 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+import { AppMountParameters, CoreSetup, CoreStart, Plugin } from '@kbn/core/public';
+import { AppPluginSetupDependencies } from './types';
+import { PLUGIN_NAME } from '../common';
+
+export class FeatureFlagsExamplePlugin implements Plugin {
+  public setup(core: CoreSetup, deps: AppPluginSetupDependencies) {
+    // Register an application into the side navigation menu
+    core.application.register({
+      id: 'featureFlagsExample',
+      title: PLUGIN_NAME,
+      async mount(params: AppMountParameters) {
+        // Load application bundle
+        const { renderApp } = await import('./application');
+        // Get start services as specified in kibana.json
+        const [coreStart] = await core.getStartServices();
+        // Render the application
+        return renderApp(coreStart, params);
+      },
+    });
+
+    deps.developerExamples.register({
+      appId: 'featureFlagsExample',
+      title: PLUGIN_NAME,
+      description: 'Plugin that shows how to make use of the feature flags core service.',
+    });
+  }
+
+  public start(core: CoreStart) {}
+
+  public stop() {}
+}

examples/feature_flags_example/public/types.ts

@@ -0,0 +1,13 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+import type { DeveloperExamplesSetup } from '@kbn/developer-examples-plugin/public';
+
+export interface AppPluginSetupDependencies {
+  developerExamples: DeveloperExamplesSetup;
+}

examples/feature_flags_example/server/index.ts

@@ -0,0 +1,71 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+import type { FeatureFlagDefinitions } from '@kbn/core-feature-flags-server';
+import type { PluginInitializerContext } from '@kbn/core-plugins-server';
+
+export const featureFlags: FeatureFlagDefinitions = [
+  {
+    key: 'example-boolean',
+    name: 'Example boolean',
+    description: 'This is a demo of a boolean flag',
+    tags: ['example', 'my-plugin'],
+    variationType: 'boolean',
+    variations: [
+      {
+        name: 'On',
+        description: 'Auto-hides the bar',
+        value: true,
+      },
+      {
+        name: 'Off',
+        description: 'Static always-on',
+        value: false,
+      },
+    ],
+  },
+  {
+    key: 'example-string',
+    name: 'Example string',
+    description: 'This is a demo of a string flag',
+    tags: ['example', 'my-plugin'],
+    variationType: 'string',
+    variations: [
+      {
+        name: 'Pink',
+        value: '#D75489',
+      },
+      {
+        name: 'Turquoise',
+        value: '#65BAAF',
+      },
+    ],
+  },
+  {
+    key: 'example-number',
+    name: 'Example Number',
+    description: 'This is a demo of a number flag',
+    tags: ['example', 'my-plugin'],
+    variationType: 'number',
+    variations: [
+      {
+        name: 'Five',
+        value: 5,
+      },
+      {
+        name: 'Ten',
+        value: 10,
+      },
+    ],
+  },
+];
+
+export async function plugin(initializerContext: PluginInitializerContext) {
+  const { FeatureFlagsExamplePlugin } = await import('./plugin');
+  return new FeatureFlagsExamplePlugin(initializerContext);
+}

examples/feature_flags_example/server/plugin.ts

@@ -0,0 +1,63 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+import type {
+  PluginInitializerContext,
+  CoreSetup,
+  CoreStart,
+  Plugin,
+  Logger,
+} from '@kbn/core/server';
+import { combineLatest } from 'rxjs';
+
+import { defineRoutes } from './routes';
+
+export class FeatureFlagsExamplePlugin implements Plugin {
+  private readonly logger: Logger;
+
+  constructor(initializerContext: PluginInitializerContext) {
+    this.logger = initializerContext.logger.get();
+  }
+
+  public setup(core: CoreSetup) {
+    const router = core.http.createRouter();
+
+    // Register server side APIs
+    defineRoutes(router);
+  }
+
+  public start(core: CoreStart) {
+    // Promise form: when we need to fetch it once, like in an HTTP request
+    void Promise.all([
+      core.featureFlags.getBooleanValue('example-boolean', false),
+      core.featureFlags.getStringValue('example-string', 'white'),
+      core.featureFlags.getNumberValue('example-number', 1),
+    ]).then(([bool, str, num]) => {
+      this.logger.info(`The feature flags are:
+      - example-boolean: ${bool}
+      - example-string: ${str}
+      - example-number: ${num}
+      `);
+    });
+
+    // Observable form: when we need to react to the changes
+    combineLatest([
+      core.featureFlags.getBooleanValue$('example-boolean', false),
+      core.featureFlags.getStringValue$('example-string', 'red'),
+      core.featureFlags.getNumberValue$('example-number', 1),
+    ]).subscribe(([bool, str, num]) => {
+      this.logger.info(`The observed feature flags are:
+      - example-boolean: ${bool}
+      - example-string: ${str}
+      - example-number: ${num}
+      `);
+    });
+  }
+
+  public stop() {}
+}