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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 30000 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 360000 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.
promoteBuffers Server, ReplicaSet, Mongos boolean false Promotes Binary BSON values to native Node Buffers.
promoteValues Server, ReplicaSet, Mongos boolean true Promotes BSON values to native types where possible, set to false to only receive wrapper types.
domainsEnabled Server, ReplicaSet, Mongos boolean false Enable the wrapping of the callback in the current domain, disabled by default to avoid perf hit.
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).
maxStalenessSeconds Replicaset number null Specify a maxStalenessSeconds value for secondary reads, minimum is 90 seconds
appname Server, Replicaset, Mongos string null The name of the application that created this MongoClient instance. MongoDB 3.4 and newer will print this value in the server log upon establishing each connection. It is also recorded in the slow query log and profile collections.
loggerLevel Server, Replicaset, Mongos string null Specify the log level used by the driver logger (error/warn/info/debug)
logger Server, Replicaset, Mongos object null Specify a customer logger mechanism, can be used to log using your app level logger

Ensure your 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.