feat(cluster): rewrite cluster discovering

* Discovering process adapted from EventStore scala client
* Use DNS for first discover but also for reconnoctions (the aim is to be able to reconnect even if all nodes have new IP addresses eg. after rolling update in a cloud environment)
* Being able to perform proper unit testing

index.d.ts

@@ -1,8 +1,8 @@
 /// <reference types="node" />
 /// <reference types="Long" />
 
-import { EventEmitter } from "events";
+import { EventEmitter } from 'events';
-import { StrictEventEmitter } from "strict-event-emitter-types";
+import { StrictEventEmitter } from 'strict-event-emitter-types';
 
 // Expose classes
 export class Position {
@@ -380,6 +380,7 @@ export interface ConnectionSettings {
     // Cluster Settings
     clusterDns?: string,
     maxDiscoverAttempts?: number,
+    discoverDelay?: number,
     externalGossipPort?: number,
     gossipTimeout?: number
 }

package.json

@@ -15,6 +15,7 @@
     "pretest": "npm run build",
     "test": "nodeunit",
     "test-debug": "TESTS_VERBOSE_LOGGING=1 nodeunit",
+    "test:jest:watch": "jest --watch --coverage",
     "prepublishOnly": "npm run build && npm run gendocs",
     "gendocs": "rm -rf docs && jsdoc src -r -d docs"
   },
@@ -54,6 +55,7 @@
     "uuid": "^3.0.1"
   },
   "devDependencies": {
+    "jest": "^26.4.2",
     "jsdoc": "^3.6.3",
     "nodeunit": "^0.11.3",
     "webpack": "^4.41.2",

src/common/utils/shuffle.js

@@ -0,0 +1,25 @@
+function rndNext(min, max) {
+  min = Math.ceil(min);
+  max = Math.floor(max);
+  return Math.floor(Math.random() * (max - min)) + min;
+}
+
+function shuffle (arr, from, to) {
+  if (!to) {
+    to = arr.length - 1;
+  }
+  if (!from) {
+    from = 0;
+  }
+  const newArr = [...arr];
+  if (from >= to) return;
+  for (var current = from; current <= to; ++current) {
+    var index = rndNext(current, to + 1);
+    var tmp = newArr[index];
+    newArr[index] = newArr[current];
+    newArr[current] = tmp;
+  }
+  return newArr;
+};
+
+module.exports = shuffle;

src/core/cluster/clusterDiscoverer.js

@@ -0,0 +1,163 @@
+const ClusterInfo = require('./clusterInfo');
+const GossipSeed = require('../../gossipSeed');
+const NodeEndPoints = require('./nodeEndpoints');
+const shuffle = require('../../common/utils/shuffle');
+
+function wait(ms) {
+  return new Promise(resolve => setTimeout(resolve, ms));
+}
+
+/**
+ * ClusterDiscoverer
+ * @constructor
+ * @class
+ * @param {Logger} log - Logger instance
+ * @param {Object} settings - Settings object
+ * @param {Object} dnsService - DNS service to perform DNS lookup
+ * @param {Object} httpService - HTTP service to perform http requests
+ */
+function ClusterDiscoverer(log, settings, dnsService, httpService) {
+  if (!settings.clusterDns && (!settings.seeds || settings.seeds.length === 0))
+    throw new Error('Both clusterDns and seeds are null/empty.');
+  this._log = log;
+
+  this._settings = settings;
+  this._dnsService = dnsService;
+  this._httpService = httpService;
+}
+
+/**
+ * Discover Cluster endpoints
+ * @param {Object} failedTcpEndPoint - The failed TCP endpoint which were used by the handler
+ * @returns {Promise.<NodeEndPoints>}
+ */
+ClusterDiscoverer.prototype.discover = async function (failedTcpEndPoint) {
+  let attempts = 0;
+  while (attempts++ < this._settings.maxDiscoverAttempts) {
+    try {
+      const candidates = await this._getGossipCandidates(this._settings.managerExternalHttpPort);
+      const gossipSeeds = candidates.filter(
+        (candidate) =>
+          !failedTcpEndPoint ||
+          !(candidate.endPoint.host === failedTcpEndPoint.host && candidate.endPoint.port === failedTcpEndPoint.port)
+      );
+      let gossipSeedsIndex = 0;
+      let clusterInfo;
+      do {
+        try {
+          clusterInfo = await this._clusterInfo(gossipSeeds[gossipSeedsIndex], this._settings.gossipTimeout);
+          if (!clusterInfo.bestNode) {
+            this._log.info(
+              `Discovering attempt ${attempts}/${this._settings.maxDiscoverAttempts} failed: no candidate found.`
+            );
+            continue;
+          }
+        } catch (err) {}
+      } while (++gossipSeedsIndex < gossipSeeds.length);
+      if (clusterInfo) {
+        return NodeEndPoints.createFromGossipMember(clusterInfo.bestNode);
+      }
+    } catch (err) {
+      this._log.info(
+        `Discovering attempt ${attempts}/${this._settings.maxDiscoverAttempts} failed with error: ${err}.\n${err.stack}`
+      );
+    }
+    await wait(this._settings.discoverDelay);
+  }
+  throw new Error(`Failed to discover candidate in ${this._settings.maxDiscoverAttempts} attempts.`);
+};
+
+/**
+ * Get gossip candidates either from DNS or from gossipSeeds settings
+ * @private
+ * @param {Number} managerExternalHttpPort - Http port of the manager (or the http port of the node for OSS clusters)
+ * @returns {Promise.<GossipSeed[]>}
+ */
+ClusterDiscoverer.prototype._getGossipCandidates = async function (managerExternalHttpPort) {
+  const gossipSeeds =
+    this._settings.seeds && this._settings.seeds.length > 0
+      ? this._settings.seeds
+      : (await this._resolveDns(this._settings.clusterDns)).map(
+          (address) => new GossipSeed({ host: address, port: managerExternalHttpPort }, undefined)
+        );
+  return shuffle(gossipSeeds);
+};
+
+/**
+ * Resolve the cluster DNS discovery address to retrieve belonging ip addresses
+ * @private
+ * @param {String} clusterDns - Cluster DNS discovery address
+ * @returns {Promise.<String[]>}
+ */
+ClusterDiscoverer.prototype._resolveDns = async function (clusterDns) {
+  const dnsOptions = {
+    family: 4,
+    hints: this._dnsService.ADDRCONFIG | this._dnsService.V4MAPPED,
+    all: true,
+  };
+  const result = await this._dnsService.lookup(clusterDns, dnsOptions);
+  if (!result || result.length === 0) {
+    throw new Error(`No result from dns lookup for ${clusterDns}`);
+  }
+  return result.map((address) => address.address);
+};
+
+/**
+ * Get cluster informations (gossip members)
+ * @param {GossipSeed} candidate - candidate to get informations from
+ * @param {Number} timeout - timeout for the http request
+ * @returns {Promise.<ClusterInfo>}
+ */
+ClusterDiscoverer.prototype._clusterInfo = async function (candidate, timeout) {
+  return new Promise((resolve, reject) => {
+    const options = {
+      host: candidate.endPoint.host,
+      port: candidate.endPoint.port,
+      path: '/gossip?format=json',
+      timeout: timeout,
+    };
+    if (candidate.hostHeader) {
+      options.headers = {
+        Host: candidate.hostHeader,
+      };
+    }
+
+    const request = this._httpService.request(options, (res) => {
+      if (res.statusCode !== 200) {
+        this._log.info('Trying to get gossip from', candidate, 'failed with status code:', res.statusCode);
+        reject(new Error(`Gossip candidate returns a ${res.statusCode} error`));
+        return;
+      }
+      let result = '';
+      res.on('data', (chunk) => {
+        result += chunk.toString();
+      });
+      res.on('end', function () {
+        try {
+          result = JSON.parse(result);
+        } catch (e) {
+          reject(new Error('Unable to parse gossip response'));
+        }
+        resolve(new ClusterInfo(result.members));
+      });
+    });
+
+    request.setTimeout(timeout);
+
+    request.on('timeout', () => {
+      this._log.info('Trying to get gossip from', candidate, 'timed out.');
+      request.destroy();
+      reject(new Error('Connection to gossip timed out'));
+    });
+
+    request.on('error', (error) => {
+      this._log.info('Trying to get gossip from', candidate, 'errored', error);
+      request.destroy();
+      reject(new Error('Connection to gossip errored'));
+    });
+
+    request.end();
+  });
+};
+
+module.exports = ClusterDiscoverer;

src/core/cluster/clusterInfo.js

@@ -0,0 +1,36 @@
+const MemberInfo = require('./memberInfo.js');
+
+const VNodeStates = Object.freeze({
+  Initializing: 0,
+  Unknown: 1,
+  PreReplica: 2,
+  CatchingUp: 3,
+  Clone: 4,
+  Slave: 5,
+  PreMaster: 6,
+  Master: 7,
+  Manager: 8,
+  ShuttingDown: 9,
+  Shutdown: 10
+});
+
+function ClusterInfo(members) {
+  this._members = members.map(member => new MemberInfo(member));
+
+  Object.defineProperty(this, 'bestNode', {
+    enumerable: true,
+    get: function () {
+      return this._getBestNode();
+    }
+  });
+}
+
+ClusterInfo.prototype._getBestNode = function () {
+  return this._members
+  .filter(member => member.isAlive && member.isAllowedToConnect)
+  .sort(function (a, b) {
+    return VNodeStates[b.state] - VNodeStates[a.state];
+  })[0];
+}
+
+module.exports = ClusterInfo;

src/core/cluster/memberInfo.js

@@ -0,0 +1,73 @@
+const NOT_ALLOWED_STATES = [
+  'Manager',
+  'ShuttingDown',
+  'Shutdown'
+];
+
+function MemberInfo(informations) {
+  this._instanceId = informations.instanceId;
+  this._timeStamp = informations.timeStamp;
+  this._state = informations.state;
+  this._isAlive = informations.isAlive;
+  this._internalTcpIp = informations.internalTcpIp;
+  this._internalTcpPort = informations.internalTcpPort;
+  this._internalSecureTcpPort = informations.internalSecureTcpPort;
+  this._externalTcpIp = informations.externalTcpIp;
+  this._externalTcpPort = informations.externalTcpPort;
+  this._externalSecureTcpPort = informations.externalSecureTcpPort;
+  this._internalHttpIp = informations.internalHttpIp;
+  this._internalHttpPort = informations.internalHttpPort;
+  this._externalHttpIp = informations.externalHttpIp;
+  this._externalHttpPort = informations.externalHttpPort;
+  this._lastCommitPosition = informations.lastCommitPosition;
+  this._writerCheckpoint = informations.writerCheckpoint;
+  this._chaserCheckpoint = informations.chaserCheckpoint;
+  this._epochPosition = informations.epochPosition;
+  this._epochNumber = informations.epochNumber;
+  this._epochId = informations.epochId;
+  this._nodePriority = informations.nodePriority;
+
+  Object.defineProperty(this, 'state', {
+    enumerable: true,
+    get: function () {
+      return this._state;
+    }
+  });
+
+  Object.defineProperty(this, 'isAllowedToConnect', {
+    enumerable: true,
+    get: function () {
+      return !NOT_ALLOWED_STATES.includes(this._state);
+    }
+  });
+
+  Object.defineProperty(this, 'isAlive', {
+    enumerable: true,
+    get: function () {
+      return this._isAlive;
+    }
+  });
+
+  Object.defineProperty(this, 'externalTcpIp', {
+    enumerable: true,
+    get: function () {
+      return this._externalTcpIp;
+    }
+  });
+
+  Object.defineProperty(this, 'externalTcpPort', {
+    enumerable: true,
+    get: function () {
+      return this._externalTcpPort;
+    }
+  });
+
+  Object.defineProperty(this, 'externalSecureTcpPort', {
+    enumerable: true,
+    get: function () {
+      return this._externalSecureTcpPort;
+    }
+  });
+}
+
+module.exports = MemberInfo;

src/core/cluster/nodeEndpoints.js

@@ -0,0 +1,23 @@
+function NodeEndPoints(tcpEndPoint, secureTcpEndPoint) {
+  if (tcpEndPoint === null && secureTcpEndPoint === null) throw new Error('Both endpoints are null.');
+  Object.defineProperties(this, {
+    tcpEndPoint: {
+      enumerable: true,
+      value: tcpEndPoint
+    },
+    secureTcpEndPoint: {
+      enumerable: true,
+      value: secureTcpEndPoint
+    }
+  });
+}
+
+NodeEndPoints.createFromGossipMember = function (member) {
+  const normTcp = { host: member.externalTcpIp, port: member.externalTcpPort };
+  const secTcp = member.externalSecureTcpPort > 0
+    ? { host: member.externalTcpIp, port: member.externalSecureTcpPort }
+    : null;
+  return new NodeEndPoints(normTcp, secTcp);
+}
+
+module.exports = NodeEndPoints

src/eventStoreConnection.js

@@ -1,9 +1,19 @@
 var EventStoreNodeConnection = require('./eventStoreNodeConnection');
 var StaticEndpointDiscoverer = require('./core/staticEndpointDiscoverer');
-var ClusterDnsEndPointDiscoverer = require('./core/clusterDnsEndPointDiscoverer');
+var ClusterDiscoverer = require('./core/cluster/clusterDiscoverer');
 var NoopLogger = require('./common/log/noopLogger');
 var ensure = require('./common/utils/ensure');
 
+const util = require('util');
+const http = require('http');
+const dns = require('dns');
+
+const dnsService = {
+  lookup : util.promisify(dns.lookup),
+  ADDRCONFIG: dns.ADDRCONFIG,
+  V4MAPPED: dns.V4MAPPED
+};
+
 var defaultConnectionSettings = Object.freeze({
   log: new NoopLogger(),
   verboseLogging: false,
@@ -32,6 +42,7 @@ var defaultConnectionSettings = Object.freeze({
   // Cluster Settings
   clusterDns: '',
   maxDiscoverAttempts: 10,
+  discoverDelay: 500,
   externalGossipPort: 0,
   gossipTimeout: 1000
 });
@@ -80,17 +91,17 @@ function createFromClusterDns(connectionSettings, clusterDns, externalGossipPort
   var mergedSettings = merge(defaultConnectionSettings, connectionSettings || {});
   var clusterSettings = {
     clusterDns: clusterDns,
-    gossipSeeds: null,
+    seeds: null,
-    externalGossipPort: externalGossipPort,
+    managerExternalHttpPort: externalGossipPort,
     maxDiscoverAttempts: mergedSettings.maxDiscoverAttempts,
+    discoverDelay: mergedSettings.discoverDelay,
     gossipTimeout: mergedSettings.gossipTimeout
   };
-  var endPointDiscoverer = new ClusterDnsEndPointDiscoverer(mergedSettings.log,
+  var endPointDiscoverer = new ClusterDiscoverer(
-    clusterSettings.clusterDns,
+    mergedSettings.log,
-    clusterSettings.maxDiscoverAttempts,
+    clusterSettings,
-    clusterSettings.externalGossipPort,
+    dnsService,
-    clusterSettings.gossipSeeds,
+    http
-    clusterSettings.gossipTimeout
   );
   return new EventStoreNodeConnection(mergedSettings, clusterSettings, endPointDiscoverer, connectionName);
 }
@@ -101,17 +112,17 @@ function createFromGossipSeeds(connectionSettings, gossipSeeds, connectionName)
   var mergedSettings = merge(defaultConnectionSettings, connectionSettings || {});
   var clusterSettings = {
     clusterDns: '',
-    gossipSeeds: gossipSeeds,
+    seeds: gossipSeeds,
     externalGossipPort: 0,
     maxDiscoverAttempts: mergedSettings.maxDiscoverAttempts,
+    discoverDelay: mergedSettings.discoverDelay,
     gossipTimeout: mergedSettings.gossipTimeout
   };
-  var endPointDiscoverer = new ClusterDnsEndPointDiscoverer(mergedSettings.log,
+  var endPointDiscoverer = new ClusterDiscoverer(
-    clusterSettings.clusterDns,
+    mergedSettings.log,
-    clusterSettings.maxDiscoverAttempts,
+    clusterSettings,
-    clusterSettings.externalGossipPort,
+    dnsService,
-    clusterSettings.gossipSeeds,
+    http
-    clusterSettings.gossipTimeout
   );
   return new EventStoreNodeConnection(mergedSettings, clusterSettings, endPointDiscoverer, connectionName);
 }

src/gossipSeed.js

@@ -1,7 +1,8 @@
-function GossipSeed(endPoint, hostName) {
+function GossipSeed(endPoint, hostName, hostHeader) {
   if (typeof endPoint !== 'object' || !endPoint.host || !endPoint.port) throw new TypeError('endPoint must be have host and port properties.');
   this.endPoint = endPoint;
   this.hostName = hostName;
+  this.hostHeader = hostHeader;
   Object.freeze(this);
 }
 

src/transport/tcp/tcpConnection.js

@@ -160,4 +160,4 @@ TcpConnection.createConnectingConnection = function(
   return connection;
 };
 
-module.exports = TcpConnection;
+module.exports = TcpConnection;

test/fixtures/gossip.json

@@ -0,0 +1,98 @@
+{
+  "members": [
+    {
+      "instanceId": "bb16857d-373d-4233-a175-89c917a72329",
+      "timeStamp": "2020-09-02T13:53:24.234898Z",
+      "state": "Slave",
+      "isAlive": false,
+      "internalTcpIp": "10.0.0.1",
+      "internalTcpPort": 1112,
+      "internalSecureTcpPort": 0,
+      "externalTcpIp": "10.0.0.1",
+      "externalTcpPort": 1113,
+      "externalSecureTcpPort": 0,
+      "internalHttpIp": "10.0.0.1",
+      "internalHttpPort": 2112,
+      "externalHttpIp": "10.0.0.1",
+      "externalHttpPort": 2113,
+      "lastCommitPosition": 648923382,
+      "writerCheckpoint": 648936339,
+      "chaserCheckpoint": 648936339,
+      "epochPosition": 551088596,
+      "epochNumber": 201,
+      "epochId": "d8f95f4b-167a-4487-9031-4d31a507e6d9",
+      "nodePriority": 0
+    },
+    {
+      "instanceId": "b3c18dcd-6476-467a-b7b8-d6672b74e9c2",
+      "timeStamp": "2020-09-02T13:56:06.189428Z",
+      "state": "CatchingUp",
+      "isAlive": true,
+      "internalTcpIp": "10.0.0.2",
+      "internalTcpPort": 1112,
+      "internalSecureTcpPort": 0,
+      "externalTcpIp": "10.0.0.2",
+      "externalTcpPort": 1113,
+      "externalSecureTcpPort": 0,
+      "internalHttpIp": "10.0.0.2",
+      "internalHttpPort": 2112,
+      "externalHttpIp": "10.0.0.2",
+      "externalHttpPort": 2113,
+      "lastCommitPosition": -1,
+      "writerCheckpoint": 0,
+      "chaserCheckpoint": 0,
+      "epochPosition": -1,
+      "epochNumber": -1,
+      "epochId": "00000000-0000-0000-0000-000000000000",
+      "nodePriority": 0
+    },
+    {
+      "instanceId": "e802a2b5-826c-4bd5-84d0-c9d1387fbf79",
+      "timeStamp": "2020-09-02T13:56:07.391534Z",
+      "state": "Master",
+      "isAlive": true,
+      "internalTcpIp": "10.0.0.3",
+      "internalTcpPort": 1112,
+      "internalSecureTcpPort": 0,
+      "externalTcpIp": "10.0.0.3",
+      "externalTcpPort": 1113,
+      "externalSecureTcpPort": 0,
+      "internalHttpIp": "10.0.0.3",
+      "internalHttpPort": 2112,
+      "externalHttpIp": "10.0.0.3",
+      "externalHttpPort": 2113,
+      "lastCommitPosition": 649007631,
+      "writerCheckpoint": 649024685,
+      "chaserCheckpoint": 649024685,
+      "epochPosition": 649023795,
+      "epochNumber": 202,
+      "epochId": "1f17695d-6558-4d8b-ba60-2ae273b11e09",
+      "nodePriority": 0
+    },
+    {
+      "instanceId": "24bb9031-5f21-436c-a7b5-c5f03a95e938",
+      "timeStamp": "2020-09-02T13:54:39.023053Z",
+      "state": "Slave",
+      "isAlive": false,
+      "internalTcpIp": "10.0.0.4",
+      "internalTcpPort": 1112,
+      "internalSecureTcpPort": 0,
+      "externalTcpIp": "10.0.0.4",
+      "externalTcpPort": 1113,
+      "externalSecureTcpPort": 0,
+      "internalHttpIp": "10.0.0.4",
+      "internalHttpPort": 2112,
+      "externalHttpIp": "10.0.0.4",
+      "externalHttpPort": 2113,
+      "lastCommitPosition": 649007631,
+      "writerCheckpoint": 649023795,
+      "chaserCheckpoint": 649023795,
+      "epochPosition": 551088596,
+      "epochNumber": 201,
+      "epochId": "d8f95f4b-167a-4487-9031-4d31a507e6d9",
+      "nodePriority": 0
+    }
+  ],
+  "serverIp": "10.0.0.3",
+  "serverPort": 2112
+}

test/unit/core/clusterDiscoverer.test.js

@@ -0,0 +1,693 @@
+const fs = require('fs');
+const path = require('path');
+const dns = require('dns');
+
+const ClusterDiscoverer = require('../../../src/core/cluster/clusterDiscoverer');
+const ClusterInfo = require('../../../src/core/cluster/clusterInfo');
+const GossipSeed = require('../../../src/gossipSeed');
+const NodeEndPoints = require('../../../src/core/cluster/nodeEndpoints');
+
+const logger = { info: () => {} };
+
+describe('ClusterDiscoverer', () => {
+  const mockDns = {
+    ADDRCONFIG: dns.ADDRCONFIG,
+    V4MAPPED: dns.V4MAPPED,
+  };
+  const mockHttp = {};
+  const settings = {
+    clusterDns: 'my-discover.com:2113',
+    maxDiscoverAttempts: 10,
+    discoverDelay: 10,
+    managerExternalHttpPort: 2113,
+    seeds: null,
+    gossipTimeout: 1000,
+  };
+  const tClusterInfo = new ClusterInfo([
+    {
+      instanceId: 'bb16857d-373d-4233-a175-89c917a72329',
+      timeStamp: '2020-09-02T13:53:24.234898Z',
+      state: 'Slave',
+      isAlive: false,
+      internalTcpIp: '10.0.0.1',
+      internalTcpPort: 1112,
+      internalSecureTcpPort: 0,
+      externalTcpIp: '10.0.0.1',
+      externalTcpPort: 1113,
+      externalSecureTcpPort: 0,
+      internalHttpIp: '10.0.0.1',
+      internalHttpPort: 2112,
+      externalHttpIp: '10.0.0.1',
+      externalHttpPort: 2113,
+      lastCommitPosition: 648923382,
+      writerCheckpoint: 648936339,
+      chaserCheckpoint: 648936339,
+      epochPosition: 551088596,
+      epochNumber: 201,
+      epochId: 'd8f95f4b-167a-4487-9031-4d31a507e6d9',
+      nodePriority: 0,
+    },
+    {
+      instanceId: 'b3c18dcd-6476-467a-b7b8-d6672b74e9c2',
+      timeStamp: '2020-09-02T13:56:06.189428Z',
+      state: 'CatchingUp',
+      isAlive: true,
+      internalTcpIp: '10.0.0.2',
+      internalTcpPort: 1112,
+      internalSecureTcpPort: 0,
+      externalTcpIp: '10.0.0.2',
+      externalTcpPort: 1113,
+      externalSecureTcpPort: 0,
+      internalHttpIp: '10.0.0.2',
+      internalHttpPort: 2112,
+      externalHttpIp: '10.0.0.2',
+      externalHttpPort: 2113,
+      lastCommitPosition: -1,
+      writerCheckpoint: 0,
+      chaserCheckpoint: 0,
+      epochPosition: -1,
+      epochNumber: -1,
+      epochId: '00000000-0000-0000-0000-000000000000',
+      nodePriority: 0,
+    },
+    {
+      instanceId: 'e802a2b5-826c-4bd5-84d0-c9d1387fbf79',
+      timeStamp: '2020-09-02T13:56:07.391534Z',
+      state: 'Master',
+      isAlive: true,
+      internalTcpIp: '10.0.0.3',
+      internalTcpPort: 1112,
+      internalSecureTcpPort: 0,
+      externalTcpIp: '10.0.0.3',
+      externalTcpPort: 1113,
+      externalSecureTcpPort: 0,
+      internalHttpIp: '10.0.0.3',
+      internalHttpPort: 2112,
+      externalHttpIp: '10.0.0.3',
+      externalHttpPort: 2113,
+      lastCommitPosition: 649007631,
+      writerCheckpoint: 649024685,
+      chaserCheckpoint: 649024685,
+      epochPosition: 649023795,
+      epochNumber: 202,
+      epochId: '1f17695d-6558-4d8b-ba60-2ae273b11e09',
+      nodePriority: 0,
+    },
+    {
+      instanceId: '24bb9031-5f21-436c-a7b5-c5f03a95e938',
+      timeStamp: '2020-09-02T13:54:39.023053Z',
+      state: 'Slave',
+      isAlive: false,
+      internalTcpIp: '10.0.0.4',
+      internalTcpPort: 1112,
+      internalSecureTcpPort: 0,
+      externalTcpIp: '10.0.0.4',
+      externalTcpPort: 1113,
+      externalSecureTcpPort: 0,
+      internalHttpIp: '10.0.0.4',
+      internalHttpPort: 2112,
+      externalHttpIp: '10.0.0.4',
+      externalHttpPort: 2113,
+      lastCommitPosition: 649007631,
+      writerCheckpoint: 649023795,
+      chaserCheckpoint: 649023795,
+      epochPosition: 551088596,
+      epochNumber: 201,
+      epochId: 'd8f95f4b-167a-4487-9031-4d31a507e6d9',
+      nodePriority: 0,
+    },
+  ]);
+  const tClusterInfoNoBestNode = new ClusterInfo([
+    {
+      instanceId: 'bb16857d-373d-4233-a175-89c917a72329',
+      timeStamp: '2020-09-02T13:53:24.234898Z',
+      state: 'Manager',
+      isAlive: true,
+      internalTcpIp: '10.0.0.1',
+      internalTcpPort: 1112,
+      internalSecureTcpPort: 0,
+      externalTcpIp: '10.0.0.1',
+      externalTcpPort: 1113,
+      externalSecureTcpPort: 0,
+      internalHttpIp: '10.0.0.1',
+      internalHttpPort: 2112,
+      externalHttpIp: '10.0.0.1',
+      externalHttpPort: 2113,
+      lastCommitPosition: 648923382,
+      writerCheckpoint: 648936339,
+      chaserCheckpoint: 648936339,
+      epochPosition: 551088596,
+      epochNumber: 201,
+      epochId: 'd8f95f4b-167a-4487-9031-4d31a507e6d9',
+      nodePriority: 0,
+    },
+    {
+      instanceId: 'b3c18dcd-6476-467a-b7b8-d6672b74e9c2',
+      timeStamp: '2020-09-02T13:56:06.189428Z',
+      state: 'CatchingUp',
+      isAlive: false,
+      internalTcpIp: '10.0.0.2',
+      internalTcpPort: 1112,
+      internalSecureTcpPort: 0,
+      externalTcpIp: '10.0.0.2',
+      externalTcpPort: 1113,
+      externalSecureTcpPort: 0,
+      internalHttpIp: '10.0.0.2',
+      internalHttpPort: 2112,
+      externalHttpIp: '10.0.0.2',
+      externalHttpPort: 2113,
+      lastCommitPosition: -1,
+      writerCheckpoint: 0,
+      chaserCheckpoint: 0,
+      epochPosition: -1,
+      epochNumber: -1,
+      epochId: '00000000-0000-0000-0000-000000000000',
+      nodePriority: 0,
+    },
+    {
+      instanceId: 'e802a2b5-826c-4bd5-84d0-c9d1387fbf79',
+      timeStamp: '2020-09-02T13:56:07.391534Z',
+      state: 'Master',
+      isAlive: false,
+      internalTcpIp: '10.0.0.3',
+      internalTcpPort: 1112,
+      internalSecureTcpPort: 0,
+      externalTcpIp: '10.0.0.3',
+      externalTcpPort: 1113,
+      externalSecureTcpPort: 0,
+      internalHttpIp: '10.0.0.3',
+      internalHttpPort: 2112,
+      externalHttpIp: '10.0.0.3',
+      externalHttpPort: 2113,
+      lastCommitPosition: 649007631,
+      writerCheckpoint: 649024685,
+      chaserCheckpoint: 649024685,
+      epochPosition: 649023795,
+      epochNumber: 202,
+      epochId: '1f17695d-6558-4d8b-ba60-2ae273b11e09',
+      nodePriority: 0,
+    },
+    {
+      instanceId: '24bb9031-5f21-436c-a7b5-c5f03a95e938',
+      timeStamp: '2020-09-02T13:54:39.023053Z',
+      state: 'Slave',
+      isAlive: false,
+      internalTcpIp: '10.0.0.4',
+      internalTcpPort: 1112,
+      internalSecureTcpPort: 0,
+      externalTcpIp: '10.0.0.4',
+      externalTcpPort: 1113,
+      externalSecureTcpPort: 0,
+      internalHttpIp: '10.0.0.4',
+      internalHttpPort: 2112,
+      externalHttpIp: '10.0.0.4',
+      externalHttpPort: 2113,
+      lastCommitPosition: 649007631,
+      writerCheckpoint: 649023795,
+      chaserCheckpoint: 649023795,
+      epochPosition: 551088596,
+      epochNumber: 201,
+      epochId: 'd8f95f4b-167a-4487-9031-4d31a507e6d9',
+      nodePriority: 0,
+    },
+  ]);
+  const discoverer = new ClusterDiscoverer(logger, settings, mockDns, mockHttp);
+  const discovererWithGossipSeeds = new ClusterDiscoverer(
+    logger,
+    {
+      ...settings,
+      ...{
+        seeds: [
+          new GossipSeed({
+            host: '10.0.0.1',
+            port: 2113,
+          }),
+          new GossipSeed({
+            host: '10.0.0.1',
+            port: 2113,
+          }),
+          new GossipSeed({
+            host: '10.0.0.1',
+            port: 2113,
+          }),
+        ],
+      },
+    },
+    mockDns,
+    mockHttp
+  );
+
+  afterEach(() => {
+    jest.clearAllMocks();
+  });
+
+  describe('constructor', () => {
+    test('Should be defined', () => {
+      expect(discoverer).toBeDefined();
+    });
+
+    test('Should throw an error', () => {
+      expect(
+        () =>
+          new ClusterDiscoverer(
+            logger,
+            {
+              clusterDns: null,
+              maxDiscoverAttempts: 10,
+              managerExternalHttpPort: 2113,
+              seeds: null,
+              gossipTimeout: 1000,
+            },
+            mockDns,
+            mockHttp
+          )
+      ).toThrow();
+    });
+    expect(
+      () =>
+        new ClusterDiscoverer(
+          logger,
+          {
+            clusterDns: null,
+            maxDiscoverAttempts: 10,
+            managerExternalHttpPort: 2113,
+            seeds: [],
+            gossipTimeout: 1000,
+          },
+          mockDns,
+          mockHttp
+        )
+    ).toThrow();
+  });
+
+  describe('#_resolveDns', () => {
+    test('Should call lookup', async () => {
+      mockDns.lookup = jest.fn().mockResolvedValue([
+        {
+          address: '10.0.0.1',
+          family: 4,
+        },
+      ]);
+      await discoverer._resolveDns('my-discover.com:2113');
+      expect(mockDns.lookup).toHaveBeenCalledWith('my-discover.com:2113', {
+        family: 4,
+        hints: dns.ADDRCONFIG | dns.V4MAPPED,
+        all: true,
+      });
+    });
+
+    test('Should reject if dnsService fails', async () => {
+      mockDns.lookup = jest.fn().mockRejectedValue(new Error('Unexpected DNS error'));
+      await expect(discoverer._resolveDns('my-discover.com:2113')).rejects.toBeDefined();
+    });
+
+    test('Should reject if no addresses are returned', async () => {
+      mockDns.lookup = jest.fn().mockResolvedValue([]);
+      await expect(discoverer._resolveDns('my-discover.com:2113')).rejects.toEqual(
+        new Error('No result from dns lookup for my-discover.com:2113')
+      );
+    });
+
+    test('Should return a list of candidate addresses', async () => {
+      mockDns.lookup = jest.fn().mockResolvedValue([
+        {
+          address: '10.0.0.1',
+          family: 4,
+        },
+        {
+          address: '10.0.0.2',
+          family: 4,
+        },
+        {
+          address: '10.0.0.3',
+          family: 4,
+        },
+      ]);
+      const candidates = await discoverer._resolveDns('my-discover.com:2113');
+      expect(candidates).toEqual(['10.0.0.1', '10.0.0.2', '10.0.0.3']);
+    });
+  });
+
+  describe('#_clusterInfo', () => {
+    test('Should call httpService.request to get cluster informations', async () => {
+      const tCandidate = new GossipSeed(
+        {
+          host: '10.0.0.1',
+          port: '2113',
+        },
+        undefined
+      );
+      const tTimeout = 1000;
+      const requestEvents = {};
+      let responseCallback;
+      mockHttp.request = jest.fn((options, callback) => {
+        responseCallback = callback;
+        return {
+          setTimeout: jest.fn(() => ({})),
+          on: (type, callback) => {
+            requestEvents[type] = callback;
+          },
+          end: () => {},
+          destroy: () => {},
+        };
+      });
+      discoverer._clusterInfo(tCandidate, tTimeout);
+      expect(mockHttp.request).toHaveBeenCalledWith(
+        {
+          host: tCandidate.endPoint.host,
+          port: tCandidate.endPoint.port,
+          path: '/gossip?format=json',
+          timeout: tTimeout,
+        },
+        expect.anything()
+      );
+    });
+
+    test('Should call httpService.request to get cluster informations with host header', async () => {
+      const tCandidate = new GossipSeed(
+        {
+          host: '10.0.0.1',
+          port: '2113',
+        },
+        undefined,
+        'MyHost'
+      );
+      const tTimeout = 1000;
+      const requestEvents = {};
+      let responseCallback;
+      mockHttp.request = jest.fn((options, callback) => {
+        responseCallback = callback;
+        return {
+          setTimeout: jest.fn(() => ({})),
+          on: (type, callback) => {
+            requestEvents[type] = callback;
+          },
+          end: () => {},
+          destroy: () => {},
+        };
+      });
+      discoverer._clusterInfo(tCandidate, tTimeout);
+      expect(mockHttp.request).toHaveBeenCalledWith(
+        {
+          host: tCandidate.endPoint.host,
+          port: tCandidate.endPoint.port,
+          path: '/gossip?format=json',
+          timeout: tTimeout,
+          headers: {
+            Host: tCandidate.hostHeader,
+          },
+        },
+        expect.anything()
+      );
+    });
+
+    test('Should return a timeout error if the sockets fails to be connected in the specified timeout', async () => {
+      const tCandidate = new GossipSeed({
+        host: '10.0.0.1',
+        port: '2113',
+      });
+      const tTimeout = 1000;
+      const requestEvents = {};
+      let responseCallback;
+      mockHttp.request = jest.fn((options, callback) => {
+        responseCallback = callback;
+        return {
+          setTimeout: jest.fn(() => ({})),
+          on: (type, callback) => {
+            requestEvents[type] = callback;
+          },
+          end: () => {
+            requestEvents['timeout']();
+          },
+          destroy: () => {},
+        };
+      });
+      await expect(discoverer._clusterInfo(tCandidate, tTimeout)).rejects.toThrow(
+        new Error('Connection to gossip timed out')
+      );
+    });
+
+    test('Should return an error if the http request emits an error', async () => {
+      const tCandidate = new GossipSeed({
+        host: '10.0.0.1',
+        port: '2113',
+      });
+      const tTimeout = 1000;
+      const requestEvents = {};
+      let responseCallback;
+      mockHttp.request = jest.fn((options, callback) => {
+        responseCallback = callback;
+        return {
+          setTimeout: jest.fn(() => ({})),
+          on: (type, callback) => {
+            requestEvents[type] = callback;
+          },
+          end: () => {
+            requestEvents['error'](new Error('Request error'));
+          },
+          destroy: () => {},
+        };
+      });
+      await expect(discoverer._clusterInfo(tCandidate, tTimeout)).rejects.toThrow(
+        new Error('Connection to gossip errored')
+      );
+    });
+
+    test("Should return an error if the candidate doesn't returns a 200 code", async () => {
+      const tCandidate = new GossipSeed({
+        host: '10.0.0.1',
+        port: '2113',
+      });
+      const tTimeout = 1000;
+      const requestEvents = {};
+      let responseCallback;
+      mockHttp.request = jest.fn((options, callback) => {
+        responseCallback = callback;
+        return {
+          setTimeout: jest.fn(() => ({})),
+          on: (type, callback) => {
+            requestEvents[type] = callback;
+          },
+          end: () => {
+            callback({
+              statusCode: 503,
+              on: (type, callback) => {
+                responseEvents[type] = callback;
+              },
+            });
+          },
+          destroy: () => {},
+        };
+      });
+      await expect(discoverer._clusterInfo(tCandidate, tTimeout)).rejects.toThrow(
+        new Error('Gossip candidate returns a 503 error')
+      );
+    });
+
+    test('Should return an error if the response is not a valid JSON', async () => {
+      const tCandidate = new GossipSeed({
+        host: '10.0.0.1',
+        port: '2113',
+      });
+      const tTimeout = 1000;
+      let responseCallback;
+      const requestEvents = {};
+      const responseEvents = {};
+      mockHttp.request = jest.fn((options, callback) => {
+        responseCallback = callback;
+        return {
+          setTimeout: jest.fn(() => ({})),
+          on: (type, callback) => {
+            requestEvents[type] = callback;
+          },
+          end: () => {
+            callback({
+              statusCode: 200,
+              on: (type, callback) => {
+                responseEvents[type] = callback;
+              },
+            });
+            responseEvents['data']('Not a JSON response');
+            responseEvents['end']();
+          },
+          destroy: () => {},
+        };
+      });
+      await expect(discoverer._clusterInfo(tCandidate, tTimeout)).rejects.toThrow(
+        new Error('Unable to parse gossip response')
+      );
+    });
+
+    test('Should return the member informations for the cluster', async () => {
+      const tCandidate = new GossipSeed({
+        host: '10.0.0.1',
+        port: '2113',
+      });
+      const tTimeout = 1000;
+      const requestEvents = {};
+      const responseEvents = {};
+      mockHttp.request = jest.fn((options, callback) => {
+        return {
+          setTimeout: jest.fn(() => ({})),
+          on: (type, callback) => {
+            requestEvents[type] = callback;
+          },
+          end: () => {
+            callback({
+              statusCode: 200,
+              on: (type, callback) => {
+                responseEvents[type] = callback;
+              },
+            });
+            responseEvents['data'](fs.readFileSync(path.resolve(__dirname, '../../fixtures/gossip.json')));
+            responseEvents['end']();
+          },
+          destroy: () => {},
+        };
+      });
+      const infos = await discoverer._clusterInfo(tCandidate, tTimeout);
+      expect(infos).toEqual(tClusterInfo);
+    });
+  });
+
+  describe('#_getGossipCandidates', () => {
+    test('Should get from dns if gossipSeeds are empty', async () => {
+      discoverer._resolveDns = jest.fn().mockResolvedValue(['10.0.0.1', '10.0.0.2', '10.0.0.3']);
+      const candidates = await discoverer._getGossipCandidates(settings.managerExternalHttpPort);
+      expect(discoverer._resolveDns).toHaveBeenCalled();
+      expect(candidates).toHaveLength(3);
+      for (let i in candidates) {
+        expect(candidates[i]).toBeInstanceOf(GossipSeed);
+      }
+    });
+
+    test('Should get gossipSeeds if present', async () => {
+      discovererWithGossipSeeds._resolveDns = jest.fn();
+      const candidates = await discovererWithGossipSeeds._getGossipCandidates(settings.managerExternalHttpPort);
+      expect(discovererWithGossipSeeds._resolveDns).not.toHaveBeenCalled();
+      expect(candidates).toHaveLength(3);
+      for (let i in candidates) {
+        expect(candidates[i]).toBeInstanceOf(GossipSeed);
+      }
+    });
+  });
+
+  describe('#discover', () => {
+    test('Should get resolve dns discover url to get IP addresses of the eventstore node', async () => {
+      discoverer._resolveDns = jest.fn().mockResolvedValue(['10.0.0.1', '10.0.0.2', '10.0.0.3']);
+      discoverer._clusterInfo = jest.fn().mockResolvedValue(tClusterInfo);
+      await discoverer.discover();
+      expect(discoverer._resolveDns).toHaveBeenCalledWith(settings.clusterDns);
+    });
+
+    test('Should call _clusterInfo with candidate', async () => {
+      discoverer._resolveDns = jest.fn().mockResolvedValue(['10.0.0.1', '10.0.0.2', '10.0.0.3']);
+      discoverer._clusterInfo = jest.fn().mockResolvedValue(tClusterInfo);
+      await discoverer.discover();
+      expect(discoverer._clusterInfo).toHaveBeenCalledWith(
+        new GossipSeed({ host: '10.0.0.1', port: settings.managerExternalHttpPort }),
+        settings.gossipTimeout
+      );
+    });
+
+    test('Should call _clusterInfo with candidate from gossipSeed if provided', async () => {
+      discovererWithGossipSeeds._resolveDns = jest.fn().mockResolvedValue();
+      discovererWithGossipSeeds._clusterInfo = jest.fn().mockResolvedValue(tClusterInfo);
+      await discovererWithGossipSeeds.discover();
+      expect(discovererWithGossipSeeds._resolveDns).not.toHaveBeenCalled();
+    });
+
+    test('Should return the bestNode', async () => {
+      discoverer._resolveDns = jest.fn().mockResolvedValue(['10.0.0.1', '10.0.0.2', '10.0.0.3']);
+      discoverer._clusterInfo = jest.fn().mockResolvedValue(tClusterInfo);
+      const node = await discoverer.discover();
+      expect(node).toEqual(
+        new NodeEndPoints(
+          {
+            host: '10.0.0.3',
+            port: 1113,
+          },
+          null
+        )
+      );
+    });
+
+    test('Should try to call each candidates until it get clusterInfo with bestNode', async () => {
+      discoverer._resolveDns = jest.fn().mockResolvedValue(['10.0.0.1', '10.0.0.2', '10.0.0.3']);
+      discoverer._clusterInfo = jest.fn().mockImplementation(async (candidate) => {
+        if (candidate.endPoint.host === '10.0.0.3') {
+          return tClusterInfo;
+        }
+        throw new Error('Gossip candidate returns a 503 error');
+      });
+      const node = await discoverer.discover();
+      expect(node).toEqual(
+        new NodeEndPoints(
+          {
+            host: '10.0.0.3',
+            port: 1113,
+          },
+          null
+        )
+      );
+      expect(discoverer._clusterInfo).toHaveBeenCalledTimes(3);
+    });
+
+    test('Should fail if the we reach the maxDiscoverAttempts limits (no bestNode is found)', async () => {
+      discoverer._resolveDns = jest.fn().mockResolvedValue(['10.0.0.1', '10.0.0.2', '10.0.0.3']);
+      discoverer._clusterInfo = jest.fn().mockResolvedValue(tClusterInfoNoBestNode);
+      await expect(discoverer.discover()).rejects.toEqual(
+        new Error(`Failed to discover candidate in ${settings.maxDiscoverAttempts} attempts.`)
+      );
+      expect(discoverer._resolveDns).toHaveBeenCalledTimes(settings.maxDiscoverAttempts);
+      expect(discoverer._resolveDns).toHaveBeenCalledTimes(settings.maxDiscoverAttempts);
+    });
+
+    test('Should fail if the we reach the maxDiscoverAttempts limits (all resolveDns attempts fails)', async () => {
+      discoverer._resolveDns = jest.fn().mockRejectedValue(new Error('Connection to gossip timed out'));
+      await expect(discoverer.discover()).rejects.toEqual(
+        new Error(`Failed to discover candidate in ${settings.maxDiscoverAttempts} attempts.`)
+      );
+      expect(discoverer._resolveDns).toHaveBeenCalledTimes(settings.maxDiscoverAttempts);
+    });
+
+    test('Should fail if the we reach the maxDiscoverAttempts limits (all clusterInfo attempts fails)', async () => {
+      discoverer._resolveDns = jest.fn().mockResolvedValue(['10.0.0.1', '10.0.0.2', '10.0.0.3']);
+      discoverer._clusterInfo = jest.fn().mockRejectedValue(new Error('Gossip candidate returns a 503 error'));
+      await expect(discoverer.discover()).rejects.toEqual(
+        new Error(`Failed to discover candidate in ${settings.maxDiscoverAttempts} attempts.`)
+      );
+      expect(discoverer._resolveDns).toHaveBeenCalledTimes(settings.maxDiscoverAttempts);
+      expect(discoverer._resolveDns).toHaveBeenCalledTimes(settings.maxDiscoverAttempts);
+    });
+
+    test('Should try to call each candidates expect failed one until it get clusterInfo with bestNode', async () => {
+      discoverer._resolveDns = jest.fn().mockResolvedValue(['10.0.0.1', '10.0.0.2', '10.0.0.3']);
+      discoverer._clusterInfo = jest.fn().mockImplementation(async (candidate) => {
+        if (candidate.endPoint.host === '10.0.0.3') {
+          return tClusterInfo;
+        }
+        throw new Error('Gossip candidate returns a 503 error');
+      });
+      const node = await discoverer.discover({ host: '10.0.0.2', port: 2113 });
+      expect(node).toEqual(
+        new NodeEndPoints(
+          {
+            host: '10.0.0.3',
+            port: 1113,
+          },
+          null
+        )
+      );
+      expect(discoverer._clusterInfo).toHaveBeenCalledTimes(2);
+      expect(discoverer._clusterInfo).toHaveBeenCalledWith(
+        new GossipSeed({ host: '10.0.0.1', port: 2113 }),
+        settings.gossipTimeout
+      );
+      expect(discoverer._clusterInfo).toHaveBeenCalledWith(
+        new GossipSeed({ host: '10.0.0.3', port: 2113 }),
+        settings.gossipTimeout
+      );
+    });
+  });
+});