Add endpoint dedicated to surfacing the cluster upgrade state, and a …

…client-side poll.

x-pack/plugins/upgrade_assistant/public/application/app.tsx

@@ -5,7 +5,7 @@
  * 2.0.
  */
 
-import React, { useEffect, useState } from 'react';
+import React, { useState, useEffect } from 'react';
 import { Router, Switch, Route, Redirect } from 'react-router-dom';
 import { FormattedMessage } from '@kbn/i18n/react';
 import { EuiEmptyPrompt, EuiPageContent } from '@elastic/eui';
@@ -21,7 +21,7 @@ import { EsDeprecations, ComingSoonPrompt, KibanaDeprecations, Overview } from '
 
 const { GlobalFlyoutProvider } = GlobalFlyout;
 
-const App: React.FunctionComponent = () => {
+const AppWithoutPolling: React.FunctionComponent = () => {
   const {
     isReadOnlyMode,
     services: { api },
@@ -34,7 +34,7 @@ const App: React.FunctionComponent = () => {
     api.onClusterUpgradeStateChange((newClusterUpgradeState: ClusterUpgradeState) => {
       setClusterUpradeState(newClusterUpgradeState);
     });
-  }, [api, setClusterUpradeState]);
+  }, [api]);
 
   // Read-only mode will be enabled up until the last minor before the next major release
   if (isReadOnlyMode) {
@@ -118,6 +118,18 @@ const App: React.FunctionComponent = () => {
   );
 };
 
+export const App: React.FunctionComponent = () => {
+  const {
+    services: { api },
+  } = useAppContext();
+
+  // This is a hack to avoid the app getting stuck in an infinite render loop,
+  // as noted in api.ts.
+  api.useLoadClusterUpgradeStatus();
+
+  return <AppWithoutPolling />;
+};
+
 export const AppWithRouter = ({ history }: { history: ScopedHistory }) => {
   return (
     <Router history={history}>

x-pack/plugins/upgrade_assistant/public/application/lib/api.ts

@@ -15,6 +15,7 @@ import {
 } from '../../../common/types';
 import {
   API_BASE_PATH,
+  CLUSTER_UPGRADE_STATUS_POLL_INTERVAL_MS,
   DEPRECATION_LOGS_COUNT_POLL_INTERVAL_MS,
   CLOUD_BACKUP_STATUS_POLL_INTERVAL_MS,
 } from '../../../common/constants';
@@ -48,6 +49,12 @@ export class ApiService {
       throw new Error('API service has not been initialized.');
     }
     const response = _useRequest<R, ResponseError>(this.client, config);
+    // NOTE: This will cause an infinite render loop in any component that both
+    // consumes the hook calling this useRequest function and also handles
+    // cluster upgrade errors. This is because we're calling handleClusterUpgradeError
+    // every time useRequest is called, which will be on every render. If handling
+    // the cluster upgrade error causes a state change in the consuming component,
+    // that will trigger a render, which will call useRequest again, and so on.
     this.handleClusterUpgradeError<UseRequestResponse<R, ResponseError>>(response.error);
     return response;
   }
@@ -67,10 +74,18 @@ export class ApiService {
     this.client = httpClient;
   }
 
-  public onClusterUpgradeStateChange(listener: ClusterUpgradeStateListener): void {
+  public onClusterUpgradeStateChange(listener: ClusterUpgradeStateListener) {
     this.clusterUpgradeStateListeners.push(listener);
   }
 
+  public useLoadClusterUpgradeStatus() {
+    return this.useRequest({
+      path: `${API_BASE_PATH}/cluster_upgrade_status`,
+      method: 'get',
+      pollIntervalMs: CLUSTER_UPGRADE_STATUS_POLL_INTERVAL_MS,
+    });
+  }
+
   public useLoadCloudBackupStatus() {
     return this.useRequest<CloudBackupStatus>({
       path: `${API_BASE_PATH}/cloud_backup_status`,

x-pack/plugins/upgrade_assistant/server/routes/cluster_upgrade_status.ts

@@ -0,0 +1,21 @@
+/*
+ * 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; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import { API_BASE_PATH } from '../../common/constants';
+import { versionCheckHandlerWrapper } from '../lib/es_version_precheck';
+import { RouteDependencies } from '../types';
+
+export function registerClusterUpgradeStatusRoutes({ router }: RouteDependencies) {
+  router.get(
+    { path: `${API_BASE_PATH}/cluster_upgrade_status`, validate: false },
+    // We're just depending on the version check to return a 426.
+    // Otherwise we just return a 200.
+    versionCheckHandlerWrapper(async (context, request, response) => {
+      return response.ok();
+    })
+  );
+}

x-pack/plugins/upgrade_assistant/server/routes/register_routes.ts

@@ -9,6 +9,7 @@ import { RouteDependencies } from '../types';
 
 import { registerAppRoutes } from './app';
 import { registerCloudBackupStatusRoutes } from './cloud_backup_status';
+import { registerClusterUpgradeStatusRoutes } from './cluster_upgrade_status';
 import { registerESDeprecationRoutes } from './es_deprecations';
 import { registerDeprecationLoggingRoutes } from './deprecation_logging';
 import { registerReindexIndicesRoutes, registerBatchReindexIndicesRoutes } from './reindex_indices';
@@ -21,6 +22,7 @@ import { registerUpgradeStatusRoute } from './status';
 export function registerRoutes(dependencies: RouteDependencies, getWorker: () => ReindexWorker) {
   registerAppRoutes(dependencies);
   registerCloudBackupStatusRoutes(dependencies);
+  registerClusterUpgradeStatusRoutes(dependencies);
   registerESDeprecationRoutes(dependencies);
   registerDeprecationLoggingRoutes(dependencies);
   registerReindexIndicesRoutes(dependencies, getWorker);