当 DB 再次可访问时，Mongoose 连接未恢复

Question

问题是 Mongoose 在以下情况下失去连接​​：

1. Node App 已启动，一切正常（可访问数据库等）
2. 本地运行的 Mongo 服务器进程（2.6.10 版）停止，然后在 15 秒后启动，一切正常（可访问数据库等）
3. Mongo 进程已停止。
4. 向 Express 发出请求，尝试访问 DB（使用 Mongoose） - 无法按预期访问。
5. Mongo 进程已启动。
6. 发出了相同的请求，即使 Mongo 已启动，也无法访问 DB。

如果我重新启动 Node JS 应用程序，一切正常。

为什么对 Mongo 的失败查询（使用 Mongoose 版本 4.4.5）会在 DB 进程再次启动时阻止连接恢复？

我们是否应该实施重试机制来尝试恢复连接，直到 DB 变得可访问？

我已经尝试过here提到的配置，但没有成功。

任何帮助将不胜感激。

下面是我们的连接助手的示例代码：

'use strict';

const _ = require('lodash');
const mongoose = require('mongoose');
const config = require('../config');
const logger = require('../logger');

const _instance = Symbol('instance');
const _enforcer = Symbol('enforcer');
const _members = Symbol('members');

/**
 * Singleton implementation of ConnectionHelper module
 * This module is responsible to reusing common db connections in the application

 * @type {ConnectionsHelper}
 */
module.exports = class ConnectionsHelper {
  constructor(enforcer) {
    if (enforcer !== _enforcer) {
      throw new Error('invalid singleton instantiation');
    }
    initConnectionFromConfig.call(this);
  }

  /**
   * The single instance
   * @returns {*}
     */
  static get instance() {
    if (!this[_instance]) {
      this[_instance] = new ConnectionsHelper(_enforcer);
    }
    return this[_instance];
  }

  /**
   * method retrieves connection by its name
   * @param connectionKey
   * @returns {*}
   */
  getConnection(connectionKey) {
    return this[_members][connectionKey];
  }

  /**
   * method disconnects all underlying connections
   * @returns {void|MongooseThenable}
   */
  closeConnections() {
    return mongoose.disconnect();
  }
};

function initConnectionFromConfig() {
  this[_members] = {};
  const dbsConnections = config.get('dbsConnections');

  _.forEach(dbsConnections, (connection, connectionName) => {

    const protocol = connection.protocol;
    const repSetPath = connection.mongoPath.join(',');
    const options = connection.options;

    options.server = {auto_reconnect: true, socketOptions: {keepAlive: 1, connectTimeoutMS: 30000 }};
    options.replset = {socketOptions: {keepAlive: 1, connectTimeoutMS: 30000 }};

    this[_members][connectionName] = mongoose.createConnection(protocol + repSetPath, options);

    addConnectionEvents.call(this, connectionName);
  });
}

function initConnectionIfNeeded() {
  this[_members] = {};
  const dbsConnections = config.get('dbsConnections');

  _.forEach(dbsConnections, (connection, connectionName) => {
    const protocol = connection.protocol;
    const repSetPath = connection.mongoPath.join(',');
    const options = connection.options;
    //options.server = {auto_reconnect: true, socketOptions: {keepAlive: 1, connectTimeoutMS: 30000 }};
    //options.replset = {socketOptions: {keepAlive: 1, connectTimeoutMS: 30000 }};

    this[_members][connectionName] = mongoose.createConnection(protocol + repSetPath, options);
    addConnectionEvents.call(this, connectionName);
  });
}

function addConnectionEvents(connectionName) {
  const connection = this[_members][connectionName];

  connection.on('connected', () => {
    logger.debug(`Mongoose connection open`);
  });
  connection.on('error', (err) => {
    logger.debug(`Mongoose connection error: ${err}`);
  });
  connection.on('exception', (err) => {
    logger.debug(`Mongoose connection exception: ${err}`);
  });
  connection.on('disconnected', () => {
    logger.debug(`Mongoose connection disconnected`);
  });
  connection.on('reconnected', () => {
    logger.debug(`Mongoose connection reconnected`);
  });
  connection.on('open', () => {
    logger.debug(`Mongoose connection is open`);
  });
  // If the Node process ends, close the Mongoose connection
  process.on('SIGINT', () => {
    connection.close(() => {
      logger.debug(`Mongoose default connection disconnected through app termination`);
      process.exit(0);
    });
  });
}

Answer 1

我遇到了同样的问题。我所做的是在这里重新启动猫鼬：

connection.on('disconnected', () => {
    logger.debug(`Mongoose connection disconnected`);
    mongoose.connect(path);
  });

而且我还使用 setTimeout() 使其每 3 秒尝试一次。

mongoose.connection.on('disconnected', function () {  
  console.log('Mongoose default connection disconnected'); 
  console.log("Trying to reconnect");

  function connect(){
    mongoose.connect(dbPath, function(err){
      if(err) console.log("Error while trying to reconnect to MongoDB");
    });
  }
  setTimeout(connect, 3000);
});

我也使用 ForeverJS。