[Console] Proxy fallback

package.json

@@ -128,6 +128,7 @@
     "@kbn/ui-framework": "1.0.0",
     "@types/json-stable-stringify": "^1.0.32",
     "@types/lodash.clonedeep": "^4.5.4",
+    "@types/node-fetch": "2.5.3",
     "@types/react-grid-layout": "^0.16.7",
     "@types/recompose": "^0.30.5",
     "JSONStream": "1.3.5",

src/legacy/core_plugins/console/index.ts

@@ -22,6 +22,7 @@ import { first } from 'rxjs/operators';
 import { resolve, join, sep } from 'path';
 import url from 'url';
 import { has, isEmpty, head, pick } from 'lodash';
+import { LiveHostsManager } from './server/live_hosts_manager';
 
 // @ts-ignore
 import { addProcessorDefinition } from './server/api_server/es_6_0/ingest';
@@ -142,7 +143,8 @@ export default function(kibana: any) {
 
       server.route(
         createProxyRoute({
-          baseUrl: head(legacyEsConfig.hosts),
+          // baseUrl: head(legacyEsConfig.hosts),
+          liveHostsManager: new LiveHostsManager(legacyEsConfig.hosts),
           pathFilters: proxyPathFilters,
           getConfigForReq(req: any, uri: any) {
             const filteredHeaders = filterHeaders(

src/legacy/core_plugins/console/server/live_hosts_manager/index.ts

@@ -0,0 +1,20 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+export { LiveHostsManager } from './live_hosts_manager';

src/legacy/core_plugins/console/server/live_hosts_manager/live_hosts_manager.ts

@@ -0,0 +1,32 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import { findLiveHostIdx } from './utils';
+
+export class LiveHostsManager {
+  // Assume first host is live
+  private pointer = 0;
+
+  constructor(private readonly hosts: string[]) {}
+
+  async getLiveHost(): Promise<string> {
+    this.pointer = await findLiveHostIdx(this.pointer, this.hosts);
+    return this.hosts[this.pointer];
+  }
+}

src/legacy/core_plugins/console/server/live_hosts_manager/utils.ts

@@ -0,0 +1,57 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import fetch from 'node-fetch';
+
+const probe = async (host: string): Promise<{ ok: boolean }> => {
+  try {
+    await fetch(`${host}/`, { method: 'HEAD' });
+    return { ok: true };
+  } catch (e) {
+    return { ok: false };
+  }
+};
+
+const roundRobinNextIdx = (number: number, max: number) => {
+  if (number >= max) {
+    return 0;
+  }
+  return number + 1;
+};
+
+export const findLiveHostIdx = async (startIdx: number, hosts: string[]) => {
+  if ((await probe(hosts[startIdx])).ok) {
+    return startIdx;
+  }
+
+  const recurse = async (idx: number): Promise<number> => {
+    if (idx === startIdx) {
+      throw new Error('No live host found!');
+    }
+    const host = hosts[idx];
+    const result = await probe(host);
+    if (result.ok) {
+      return idx;
+    }
+    const nextId = roundRobinNextIdx(idx, hosts.length);
+    return recurse(nextId);
+  };
+
+  return await recurse(roundRobinNextIdx(startIdx, hosts.length));
+};

src/legacy/core_plugins/console/server/proxy_route.js

@@ -58,7 +58,7 @@ function getProxyHeaders(req) {
 }
 
 export const createProxyRoute = ({
-  baseUrl = '/',
+  liveHostsManager,
   pathFilters = [/.*/],
   getConfigForReq = () => ({}),
 }) => ({
@@ -100,6 +100,7 @@ export const createProxyRoute = ({
     handler: async (req, h) => {
       const { payload, query } = req;
       const { path, method } = query;
+      const baseUrl = await liveHostsManager.getLiveHost();
       const uri = toURL(baseUrl, path);
 
       // Because this can technically be provided by a settings-defined proxy config, we need to

yarn.lock

@@ -3652,6 +3652,13 @@
   dependencies:
     "@types/node" "*"
 
+"@types/[email protected]":
+  version "2.5.3"
+  resolved "https://registry.yarnpkg.com/@types/node-fetch/-/node-fetch-2.5.3.tgz#b84127facd93642b1fb6439bc630ba0612e3ec50"
+  integrity sha512-X3TNlzZ7SuSwZsMkb5fV7GrPbVKvHc2iwHmslb8bIxRKWg2iqkfm3F/Wd79RhDpOXR7wCtKAwc5Y2JE6n/ibyw==
+  dependencies:
+    "@types/node" "*"
+
 "@types/node-fetch@^2.5.0":
   version "2.5.0"
   resolved "https://registry.yarnpkg.com/@types/node-fetch/-/node-fetch-2.5.0.tgz#1c55616a4591bdd15a389fbd0da4a55b9502add5"