How do I manage MongoDB connections in a Node js web application

Question

I m using the node-mongodb-native driver with MongoDB to write a website   I have some questions about how to manage connections    Is it enough using only one MongoDB connection for all requests  Are there any performance issues  If not  can I setup a global connection to use in the whole application  If not  is it good if I open a new connection when request arrives  and close it when handled the request  Is it expensive to open and close a connection  Should I use a global connection pool  I hear the driver has a native connection pool  Is it a good choice  If I use a connection pool  how many connections should be used  Are there other things I should notice

User · Answer

You should create a connection as service then reuse it when need.

// db.service.js
import { MongoClient } from "mongodb";
import database from "../config/database";

const dbService = {
  db: undefined,
  connect: callback => {
    MongoClient.connect(database.uri, function(err, data) {
      if (err) {
        MongoClient.close();
        callback(err);
      }
      dbService.db = data;
      console.log("Connected to database");
      callback(null);
    });
  }
};

export default dbService;

my App.js sample

// App Start
dbService.connect(err => {
  if (err) {
    console.log("Error: ", err);
    process.exit(1);
  }

  server.listen(config.port, () => {
    console.log(`Api runnning at ${config.port}`);
  });
});

and use it wherever you want with

import dbService from "db.service.js"
const db = dbService.db

User · Answer

Here is some code that will manage your MongoDB connections   var MongoClient   require  mongodb   MongoClient  var url   require     config json    MongoDBURL    var option       db       numberOfRetries   5        server        auto reconnect  true      poolSize   40      socketOptions            connectTimeoutMS  500              replSet        mongos         function MongoPool      var p db   function initPool cb     MongoClient connect url  option  function err  db        if  err  throw err       p db   db      if cb  amp  amp  typeof cb      function           cb p db           return MongoPool     MongoPool initPool   initPool   function getInstance cb     if  p db       initPool cb        else      if cb  amp  amp  typeof cb      function         cb p db         MongoPool getInstance   getInstance   module exports   MongoPool    When you start the server  call initPool  require  mongo-pool   initPool      Then in any other module you can do the following   var MongoPool   require  mongo-pool    MongoPool getInstance function  db          Query your MongoDB database        This is based on MongoDB documentation  Take a look at it

User · Answer

I have implemented below code in my project to implement connection pooling in my code so it will create a minimum connection in my project and reuse available connection      Mongo js    var MongoClient   require  mongodb   MongoClient  var url    mongodb   localhost 27017 yourdatabasename    var assert   require  assert     var connection        Create the database connection establishConnection   function callback                    MongoClient connect url    poolSize  10   function err  db                        assert equal null  err                            connection   db                         if typeof callback      function   amp  amp  callback                                callback connection                                                  function getconnection        return connection    module exports          establishConnection establishConnection      getconnection getconnection      app js      establish one connection with all other routes will use  var db   require    routes mongo    db establishConnection       you can also call with callback if you wanna create any collection at starting    db establishConnection function conn     conn createCollection  collectionName   function err  res        if  err  throw err      console log  Collection created                     anyother route js  var db   require    mongo    router get      function req  res  next        var connection   db getconnection       res send  Hello

User · Answer

I have been using generic-pool with redis connections in my app - I highly recommend it  Its generic and I definitely know it works with mysql so I don t think you ll have any problems with it and mongo  https   github com coopernurse node-pool

User · Answer

Manage mongo connection pools in a single self contained module  This approach provides two benefits  Firstly it keeps your code modular and easier to test  Secondly your not forced to mix your database connection up in your request object which is NOT the place for a database connection object   Given the nature of JavaScript I would consider it highly dangerous to mix in anything to an object constructed by library code   So with that you only need to Consider a module that exports two methods  connect        gt  Promise and get        gt  dbConnectionObject   With such a module you can firstly connect to the database     runs in boot js or what ever file your application starts with const db   require    myAwesomeDbModule    db connect        then      gt  console log  database connected         then      gt  bootMyApplication         catch  e    gt            console error e              Always hard exit on a database connection error         process exit 1             When in flight your app can simply call get   when it needs a DB connection   const db   require    myAwesomeDbModule    db get   find            I have excluded code here to keep the example  simple   If you set up your db module in the same way as the following not only will you have a way to ensure that your application will not boot unless you have a database connection you also have a global way of accessing your database connection pool that will error if you have not got a connection      myAwesomeDbModule js let connection   null   module exports connect        gt  new Promise  resolve  reject    gt        MongoClient connect url  option  function err  db            if  err    reject err   return             resolve db           connection   db               module exports get        gt        if  connection            throw new Error  Call connect first                return connection

User · Answer

If you have Express js  you can use express-mongo-db for caching and sharing the MongoDB connection between requests without a pool  since the accepted answer says it is the right way to share the connection    If not - you can look at its source code and use it in another framework

User · Answer

Best approach to implement connection pooling is you should create one global array variable which hold db name with connection object returned by MongoClient and then reuse that connection whenever you need to contact Database    In your Server js define var global dbconnections       Create a Service naming connectionService js  It will have 2 methods getConnection and createConnection  So when user will call getConnection    it will find detail in global connection variable and return connection details if already exists else it will call createConnection   and return connection Details  Call this service using db name and it will return connection object if it already have else it will create new connection and return it to you    Hope it helps     Here is the connectionService js code   var mongo   require  mongoskin    var mongodb   require  mongodb    var Q   require  q    var service       service getConnection   getConnection   module exports   service   function getConnection appDB       var deferred   Q defer        var connectionDetails global dbconnections find item  gt item appDB  appDB       if connectionDetails  deferred resolve connectionDetails connection        else createConnection appDB  then function connectionDetails               deferred resolve connectionDetails               return deferred promise     function createConnection appDB       var deferred   Q defer        mongodb MongoClient connect connectionServer   appDB   err database   gt                 if err  deferred reject err name          err message           global dbconnections push  appDB  appDB   connection  database            deferred resolve database               return deferred promise

User · Answer

Open a new connection when the Node js application starts  and reuse the existing db connection object    server js  import express from  express   import Promise from  bluebird   import logger from  winston   import   MongoClient   from  mongodb   import config from    config   import usersRestApi from    api users    const app   express     app use   api users   usersRestApi    app get       req  res    gt      res send  Hello World            Create a MongoDB connection pool and start the application    after the database connection is ready MongoClient connect config database url    promiseLibrary  Promise     err  db    gt      if  err        logger warn  Failed to connect to the database    err stack           app locals db   db    app listen config port       gt        logger info  Node js app is listening at http   localhost   config port                  api users js  import   Router   from  express   import   ObjectID   from  mongodb    const router   new Router     router get    id   async  req  res  next    gt      try       const db   req app locals db      const id   new ObjectID req params id       const user   await db collection  user   findOne    id  id            email  1        firstName  1        lastName  1              if  user          user id   req params id        res send user         else         res sendStatus 404             catch  err        next err            export default router    Source  How to Open Database Connections in a Node js Express App

User · Answer

If using express there is another more straightforward method  which is to utilise Express s built in feature to share data between routes and modules within your app  There is an object called app locals  We can attach properties to it and access it from inside our routes  To use it  instantiate your mongo connection in your app js file   var app   express     MongoClient connect  mongodb   localhost 27017     then client   gt     const db   client db  your-db      const collection   db collection  your-collection      app locals collection   collection                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       view engine setup app set  views   path join   dirname   views       This database connection  or indeed any other data you wish to share around the modules of you app can now be accessed within your routes with req app locals as below without the need for creating and requiring additional modules   app get       req  res    gt      const collection   req app locals collection    collection find     toArray      then response   gt  res status 200  json response      catch error   gt  console error error          This method ensures that you have a database connection open for the duration of your app unless you choose to close it at any time  It s easily accessible with req app locals your-collection and doesn t require creation of any additional modules

User · Answer

mongodb com -  new project -  new cluster -  new collection -  connect -  IP address  0 0 0 0 0  amp  db cred -  connect your application -  copy connection string and paste in  env file of your node app and make sure to replace    with the actual password for the user and also replace   test  with your db name  create new file  env   CONNECTIONSTRING x -- gt  const client   new MongoClient CONNECTIONSTRING   PORT 8080  JWTSECRET mysuper456secret123phrase

User · Answer

The primary committer to node-mongodb-native says      You open do MongoClient connect once when your app boots up and reuse   the db object  It s not a singleton connection pool each  connect   creates a new connection pool    So  to answer your question directly  reuse the db object that results from MongoClient connect    This gives you pooling  and will provide a noticeable speed increase as compared with opening closing connections on each db action

[node.js] How do I manage MongoDB connections in a Node.js web application?

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