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Connection Options

Overview

In this guide, you can learn about MongoDB connection and authentication options. You can set connection options as parameters of your connection string to specify how your Client instance behaves while connected to the server.

Option Name	Accepted Values	Default Value	Description
appName	String	None	Specifies the application name that the `Client` instance sends to the server as part of the handshake. Specifying an `appName` can help you use the server logs to determine which `Client` instance is connected to the server.
authMechanism	String	None	Specifies which authentication mechanism to use. If you do not specify this option, the driver uses the default authentication mechanism. To learn more about authentication in the Rust driver, see the guide on Authentication Mechanisms.
authMechanismProperties	String	None	Specifies more properties for the authentication mechanism set in the `authMechanism` option.
authSource	String	See description	Specifies the database used to authenticate. This option defaults to `admin` for SCRAM-based authentication mechanisms, `$external` for the `MONGODB-X509` mechanism, and the database name or `$external` for the `PLAIN` mechanism.
compressors	A comma-separated list of strings	None	Specifies compressors that the `Client` instance uses in the specified order. To learn more about network compression, see the Network Compression guide.
connectTimeoutMS	Non-negative integer	`10000` (10 seconds)	Specifies the connection timeout, in milliseconds, passed to each underlying TCP stream when attempting to connect to the server.
directConnection	Boolean	`false`	Specifies whether the `Client` instance directly connects to a single host instead of discovering and connecting to all servers in the cluster.
heartbeatFrequencyMS	Integer greater than or equal to 500	`10000` (10 seconds)	Specifies the amount of time in milliseconds that each monitoring thread waits between performing server checks.
journal	Boolean	`false`	Requests acknowledgment that the operation propagated to the on-disk journal.
localThresholdMS	Non-negative integer	15	Specifies the amount of time in milliseconds that the average round-trip time between the driver and server can last compared to the shortest round-trip time of all the suitable servers. A value of `0` indicates that there is no latency window, so only the server with the lowest average round-trip time is eligible.
maxIdleTimeMS	Non-negative integer	`0` (no limit)	Specifies the amount of time in milliseconds that a connection can remain idle in a connection pool before the server closes it. A value of `0` indicates that the client does not close idle connections. Set this value higher than your application's expected idle period but lower than firewall or proxy connection timeouts to prevent unexpected disconnections.
maxStalenessSeconds	`-1`, or any integer greater than or equal to `90`	`-1`	Specifies the maximum lag, in seconds, behind the primary node that a secondary node can be to be considered for the given operation. The value of this option must be at least `90`, or the operation raises an error. A value of `-1` means there is no maximum lag.
maxPoolSize	Non-negative integer	`10`	Specifies the maximum number of connections that the `Client` instance can create in a connection pool for a given server. If you attempt an operation while the value of `maxPoolSize` connections are checked out, the operation waits until an in-progress operation finishes and the connection returns to the pool.
minPoolSize	Non-negative integer	`0`	Specifies the minimum number of connections that are available in a server's connection pool at a given time. If fewer than `minPoolSize` connections are in the pool, the server adds connections in the background up to the value of `minPoolSize`.
readConcernLevel	String	None	Specifies the default read concern for operations performed on the `Client` instance. To learn more, see Read Concern in the Server manual.
readPreference	String	`primary`	Specifies how the driver routes a read operation to members of a replica set. To learn more, see Read Preference in the Server manual.
readPreferenceTags	A list of comma-separated key-value pairs	None	Specifies which replica set members are considered for operations. Each instance of this key is a separate tag set. The driver checks each tag set until it finds one or more servers with each tag in the set.
replicaSet	String	None	Specifies the name of the replica set that the `Client` instance connects to.
retryReads	Boolean	`true`	Specifies whether the client retries a read operation if the operation fails.
serverSelectionTimeoutMS	Non-negative integer	`30000` (30 seconds)	Specifies the amount of time in milliseconds that the `Client` instance waits when attempting to select a server for an operation before timing out.
tls	Boolean	`false`	Specifies the TLS configuration for the `Client` instance to use in its connections with the server. By default, TLS is off.
tlsAllowInvalidCertificates	Boolean	`false`	Specifies whether the `Client` instance returns an error if the server presents an invalid certificate. We recommend that you set this option to `true` only in testing environments to avoid creating vulnerabilities in your application.
tlsCAFile	String	See description	Specifies the path to the certificate authority (CA) file that the `Client` instance uses for TLS. If you do not specify this option, the driver uses the Mozilla root certificates from the `webpki-roots` crate.
tlsCertificateKeyFile	String	None	Specifies the path to the certificate file that the `Client` instance presents to the server to verify its identify. If you do not set this option, the `Client` instance does not attempt to verify its identity to the server.
tlsInsecure	Boolean	`false`	Specifies whether the `Client` instance returns an error if the server presents an invalid certificate. We recommend that you set this option to `true` only in testing environments to avoid creating vulnerabilities in your application.
w	Non-negative integer or string	None	Requests acknowledgment that the operation has propagated to a specific number or variety of servers. To learn more, see Write Concern in the Server manual.
wTimeoutMS	Non-negative integer	No timeout	Specifies a time limit, in milliseconds, for the write concern. If an operation has not propagated to the requested level within the time limit, the driver raises an error.
zlibCompressionLevel	Integer between -1 and 9 (inclusive)	`-1`	Specifies the level field of the `zlib` compression if you use that compressor. Setting a value of `-1` selects the default compression level (`6`). Setting a value of `0` specifies no compression, and setting a value of `9` specifies maximum compression. To learn more about network compression, see the Network Compression guide.

To see a full list of connection options, visit the Connection String Options section of the Server manual entry on Connection Strings.

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Connection Guide

Network Compression