MongoDB Cluster with 3 Linux Instances

Setup MongoDB Cluster

Prerequisite

Require two or more servers to set cluster

Ubuntu 22.04

Follow the below steps to set up a 3-node MongoDB cluster:

Configuration and installation

Update && Upgrade the system

Before processing, update and upgrade all packages.

sudo apt-get update -y && sudo apt-get upgrade -y

Check your current hostname by running the following command:

hostname

Set the Hostname in each server

To change the hostname, you can use the hostnamectl command. For example, to set the hostname to "hostname", you would run.

sudo hostnamectl set-hostname myhostname

On Linux and Unix-like systems, the hosts file is located in the /etc/ directory. To edit this file on each of your three servers, use your preferred text editor.

sudo vi /etc/hosts

Server Hostname Configuration

Configuring your servers with descriptive hostnames is advisable as it enhances clarity and ease of management.

• mongo0.replset.member

• mongo1.replset.member

• mongo2.replset.member

Using these hostnames, your /etc/hosts files would look similar to the following highlighted lines:

To add the MongoDB GPG key

Import the MongoDB GPG Key

First, import the MongoDB GPG key to verify the authenticity of the software packages:

To get the latest version of the software, add MongoDB’s dedicated package repository to your APT sources. Then, install the meta-package that always points to the newest MongoDB version.

First, import the public GPG key for the latest stable version of MongoDB using the following command:

sudo wget -qO - https://www.mongodb.org/static/pgp/server-4.4.asc | sudo apt-key add -

Add MongoDB Repository

Next, add the MongoDB repository to your system's list:

APT (Advanced Package Tool) uses two main locations for finding online package repositories: the sources.list file and the sources.list.d directory. The sources.list file lists repository sources line-by-line, placing the most preferred at the top. The sources.list.d directory allows for modular and organized management by maintaining additional repository sources in separate files.

Execute the following command to create a file named mongodb-org-4.4.list in the sources.list.d directory:

sudo echo "deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu $(lsb_release -sc)/mongodb-org/4.4 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-4.4.list

After executing this command, refresh your server’s local package index to ensure APT can locate the MongoDB-org package:

sudo apt-get update -y

Install MongoDB

Now, you can install MongoDB using the following command:

sudo apt-get install mongodb-org -y

This command will install the MongoDB package and its dependencies.

Start MongoDB Service

After installing MongoDB, it should start automatically. To check the service status, run:

sudo systemctl start mongod
sudo systemctl status mongod

Enable MongoDB to Start on the Boot

sudo systemctl enable mongod

Verify Installation

To verify that MongoDB is installed successfully, open the MongoDB shell by following these steps:

sudo mongo --version

sudo mongo

Enable Replication in Each Server's

MongoDB Configuration File:-

You have successfully configured the /etc/hosts file on your servers to map hostnames to their respective IP addresses.

To change MongoDB settings, edit the primary configuration file found at /etc/mongod.conf. This file is created automatically during installation.

Use a text editor vi to open and modify the file. Here’s the command:

sudo vi /etc/mongod.conf

In MongoDB, various configuration options allow you to customize the server's behavior. The system log option manages the database’s logging settings, enabling you to specify what gets logged and where. Conversely, the net option is essential for configuring network-related settings, providing control over parameters such as port configuration and network interfaces.

Update the IP address in each server from 127.0.0.0 to 0.0.0.0.

Create a mongo key file in each server

sudo mkdir -p /etc/mongodb/key-files/

Now create an OpenSSL and run these commands

sudo openssl rand  -base64  756 > /etc/mongodb/key-files/mongo-key

Copy these mongo-key files in another 2 vms

$ sftp root@your_IP_address

Enabling Replication in Each Server's MongoDB Configuration File

After copying the necessary files, proceed by adding the specified keys to the /etc/mongod.conf file on each server.

sudo vi /etc/mongod.conf

Uncomment the security option and add the key

Add the key

keyFile: /etc/mongodb/key-files/mongo-key

Configure the file permissions and ownership in each server

sudo chmod 400 /etc/mongodb/key-files/mongo-key
sudo chown -R mongodb:mongodb /etc/mongodb

Before executing the following command, ensure the Mongod service is stopped.

sudo systemctl stop mongod

Replication runs these commands in all nodes for set replace

sudo /usr/bin/mongod --replSet "evermight" --config /etc/mongod.conf --fork 

Also, add replication of all nodes

sudo systemctl start mongod

Starting the Replica Set and Adding Members:

After setting up your three MongoDB instances, initiate replication by opening a MongoDB shell and adding each instance as a replication member.

sudo mongo

To begin the replication process, execute these commands:

mongo> rs.initiate({_id: "evermight", members: [{_id: 1, host: "mongo1"},{_id: 2, host: "mongo2"}] });

Conclusion

MongoDB is a free, open-source NoSQL database management system (DBMS) popular for large-scale websites or applications. Since it doesn’t use a fixed schematic structure to store data, it is more flexible and scalable than SQL.