MongoDB Cheat Sheet

Jul 09, 2024

Table of Contents

• MongoDB Shell - Mongosh
• Connect to a Local Instance
• Users
• List All Users
• Create a User
• RS - Replica Sets
• Check Which Server is the Master
• Get the Status of the ReplicaSet
• Change the Master

Related to:: MongoDB

MongoDB Shell - Mongosh §

Connect to a Local Instance §

mongosh --port 27017  --authenticationDatabase "admin" -u "adminUser"

Users §

List All Users §

use admin
db.system.users.find()

Create a User §

The most used roles are: read, readWrite, dbAdmin, userAdmin and clusterMonitor (see the full list at Built-In Roles - MongoDB Manual v7.0)

use admin
db.createUser({
    user: "mainUserName",
    pwd:  "secret123", 
    roles: [ 
        { role: "read", db: "mainDatabaseName" },
        { role: "readWrite", db: "secondaryDatabaseName" },
    ]
})

RS - Replica Sets §

Check Which Server is the Master §

db.runCommand("ismaster")

Get the Status of the ReplicaSet §

rs.status();

Change the Master §

While connected to the master, the following could be run to make member 2 of the RS become the master. The idea is to make all the secondaries a 0.5 priority and the master 1. If we have more than 3 servers, we can follow the same principle for the other servers.

cfg = rs.conf()
cfg.members[0].priority = 0.5
cfg.members[1].priority = 0.5
cfg.members[2].priority = 1
rs.reconfig(cfg)