URI Connection Settings

Optional connection settings are settings not covered by the URI Connection String . The following options are passed in the options parameter in the MongoClient.connect function.

var MongoClient = require('mongodb').MongoClient
  , assert = require('assert');

// Connection URL
var url = 'mongodb://localhost:50000,localhost:50001/myproject';
// Use connect method to connect to the Server passing in
// additional options
MongoClient.connect(url, {
  poolSize: 10, ssl: true
}, function(err, db) {
  assert.equal(null, err);
  console.log("Connected correctly to server");

  db.close();
});

The table below shows all settings and what topology they affect.

Option	Affects	Type	Default	Description
poolSize	Server, ReplicaSet, Mongos	integer	5	Set the maximum poolSize for each individual server or proxy connection.
ssl	Server, ReplicaSet, Mongos	boolean	false	Use ssl connection (needs to have a mongod server with ssl support)
sslValidate	Server, ReplicaSet, Mongos	boolean	true	Validate mongod server certificate against ca (needs to have a mongod server with ssl support, 2.4 or higher)
sslCA	Server, ReplicaSet, Mongos	Array	null	Array of valid certificates either as Buffers or Strings (needs to have a mongod server with ssl support, 2.4 or higher)
sslCert	Server, ReplicaSet, Mongos	Buffer/String	null	String or buffer containing the certificate we wish to present (needs to have a mongod server with ssl support, 2.4 or higher)
sslKey	Server, ReplicaSet, Mongos	Buffer/String	null	String or buffer containing the certificate private key we wish to present (needs to have a mongod server with ssl support, 2.4 or higher)
sslPass	Server, ReplicaSet, Mongos	Buffer/String	null	String or buffer containing the certificate password (needs to have a mongod server with ssl support, 2.4 or higher)
autoReconnect	Server	boolean	true	Reconnect on error.
noDelay	Server, ReplicaSet, Mongos	boolean	true	TCP Socket NoDelay option.
keepAlive	Server, ReplicaSet, Mongos	integer	0	The number of milliseconds to wait before initiating keepAlive on the TCP socket.
connectTimeoutMS	Server, ReplicaSet, Mongos	integer	30000	TCP Connection timeout setting.
socketTimeoutMS	Server, ReplicaSet, Mongos	integer	30000	TCP Socket timeout setting.
reconnectTries	Server	integer	30	Server attempt to reconnect #times
reconnectInterval	Server	integer	1000	Server will wait # milliseconds between retries.
ha	ReplicaSet, Mongos	boolean	true	Turn on high availability monitoring.
haInterval	ReplicaSet, Mongos	integer	10000,5000	Time between each replicaset status check.
replicaSet	ReplicaSet	string	null	The name of the replicaset to connect to.
secondaryAcceptableLatencyMS	ReplicaSet	integer	15	Sets the range of servers to pick when using NEAREST (lowest ping ms + the latency fence, ex: range of 1 to (1 + 15) ms).
acceptableLatencyMS	Mongos	integer	15	Sets the range of servers to pick when using NEAREST (lowest ping ms + the latency fence, ex: range of 1 to (1 + 15) ms).
connectWithNoPrimary	ReplicaSet	boolean	false	Sets if the driver should connect even if no primary is available.
authSource	Server, ReplicaSet, Mongos	string	null	If the database authentication is dependent on another databaseName.
w	Server, ReplicaSet, Mongos	string, integer	null	The write concern.
wtimeout	Server, ReplicaSet, Mongos	integer	null	The write concern timeout value.
j	Server, ReplicaSet, Mongos	boolean	false	Specify a journal write concern.
forceServerObjectId	Server, ReplicaSet, Mongos	boolean	false	Force server to assign _id values instead of driver.
serializeFunctions	Server, ReplicaSet, Mongos	boolean	false	Serialize functions on any object.
ignoreUndefined	Server, ReplicaSet, Mongos	boolean	false	Specify if the BSON serializer should ignore undefined fields.
raw	Server, ReplicaSet, Mongos	boolean	false	Return document results as raw BSON buffers.
promoteLongs	Server, ReplicaSet, Mongos	boolean	true	Promotes Long values to number if they fit inside the 53 bits resolution.
bufferMaxEntries	Server, ReplicaSet, Mongos	integer	-1	Sets a cap on how many operations the driver will buffer up before giving up on getting a working connection, default is -1 which is unlimited.
readPreference	Server, ReplicaSet, Mongos	object	null	The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
pkFactory	Server, ReplicaSet, Mongos	object	null	A primary key factory object for generation of custom _id keys.
promiseLibrary	Server, ReplicaSet, Mongos	object	null	A Promise library class the application wishes to use such as Bluebird, must be ES6 compatible.
readConcern	Server, ReplicaSet, Mongos	object	null	Specify a read concern for the collection. (only MongoDB 3.2 or higher supported).

Ensure you connection string is valid for Replica Sets

The connection string passed to the driver must use the fully qualified host names for the servers as set in the replicaset config. Given the following configuration settings for your replicaset.

{
	"_id" : "testSet",
	"version" : 1,
	"protocolVersion" : 1,
	"members" : [
		{
			"_id" : 1,
			"host" : "server1:31000",
		},
		{
			"_id" : 2,
			"host" : "server2:31001",
		},
		{
			"_id" : 3,
			"host" : "server3:31002",
		}
	]
}

You must ensure server1, server2 and server3 are resolvable from the driver for the Replicaset discovery and failover to work correctly.

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