To begin interacting with a MongoDB database, the database service must be initialized. Navigate to the bin directory within your MongoDB installation folder and execute the mongod command. Upon execution, the server will initialize and wait for incoming connections. Once a client establishes a connection, the terminal will display relevant log entries.

While this guide utilizes the MongoDB shell for demonstration, connection strings are standardized across various drivers, including those for PHP, Python, and Node.js.

Standard URI Connection Syntax

MongoDB utilizes a uniform resource identifier (URI) string to define connection parameters. The standard structure is as follows:

mongodb://[username:password@]host1[:port1][,host2[:port2],...[,hostN[:portN]]][/[database][?options]]

Parameter Breakdown:

• mongodb://: A mandatory prefix indicating the protocol.
• username:password@: Optional credentials for authentication. If provided, the driver will attempt to authenticate against the specified database.
• host1: The hostname or IP address of the target server. At least one host is required. Multiple hosts should be listed for replica sets.
• portX: Optional port number. Defaults to 27017 if omitted.
• /database: The authentication data base. If credentials are provided but this is omitted, the default is the test database.
• ?options: Connection specific settings presented as key-value pairs (e.g., key=value), separated by ampersands (&) or semicolons (;).

Connection Options

The connection string supports various options to modify behavior. The following table outlines common parameters:

Usage Examples

Connecting to the local instance on the default port:

mongodb://localhost

Connecting via the MongoDB Shell:

$ ./mongo
MongoDB shell version v4.4.0
connecting to: mongodb://127.0.0.1:27017/?compressors=disabled&gssapiServiceName=mongodb
Implicit session: session { "id" : UUID("...") }
MongoDB server version: 4.4.0

Authenticating with a username and password:

The syntax requires the credentials followed by the host. To connect as user db_admin with password securePass:

mongodb://db_admin:securePass@localhost/

To authenticate against a specific data base (e.g., app_data):

mongodb://db_admin:securePass@localhost/app_data

Advanced Scenarios

Connecting to a specific database with credentials:

mongodb://app_user:accessCode@192.168.1.10/production_db

Connecting to a Replica Pair:

mongodb://node1.example.com:27017,node2.example.com:27017

Connecting to a Replica Set (three nodes):

mongodb://primary,secondary1:27018,secondary2:27019

Replica Set with read preference set to secondaries:

mongodb://hostA,hostB,hostC/?slaveOk=true

Direct connection to a specific node (ignoring replica set state):

mongodb://hostA,hostB,hostC/?connect=direct;slaveOk=true

Safe Mode connection (Write Concern):

mongodb://localhost/?safe=true

Replica Set with Write Concern and Timeout:

Ensures writes are propagated to at least 2 nodes within 2 seconds:

mongodb://hostA,hostB,hostC/?safe=true;w=2;wtimeoutMS=2000