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Setting Up a MongoDB Cluster Using Linux Instances

MongoDB is a highly scalable, open-source NoSQL database system, ideal for managing large amounts of data across distributed environments. It excels in high-volume data storage, supporting features like ad-hoc queries, indexing, load balancing, aggregation, and even server-side JavaScript execution. MongoDB organizes data into collections and documents rather than tables and rows, using key-value pairs within each document. This flexible data model, combined with its built-in replication and sharding capabilities, makes MongoDB a popular choice for applications requiring high availability and horizontal scaling.

In this guide, we will walk you through setting up a three-node MongoDB replica set on Ubuntu 22.04, which can be extended further as needed.

Prerequisites​

  • Operating System: Ubuntu 22.04
  • MongoDB Version: 4.4 (or latest stable version)
  • At least 3 Linux servers (these will act as MongoDB instances for the replica set)
  • Basic Linux administration skills (e.g., SSH access, using a text editor, and managing services)

Step 1: Update and Upgrade System Packages​

Start by updating your system to ensure that all packages are up to date.

  • To update and upgrade system packages, run:
sudo apt-get update -y && sudo apt-get upgrade -y

Step 2: Set Hostnames for Each Server​

You’ll need to configure a descriptive hostname for each MongoDB node in the cluster.

  • Check the current hostname of the server:
hostname
  • Change the hostname using the following command:
sudo hostnamectl set-hostname myhostname
  • Edit the /etc/hosts file on all three servers to ensure that each MongoDB instance can resolve the other nodes by their hostnames:
sudo vi /etc/hosts

Example content for /etc/hosts:

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

Step 3: Import MongoDB GPG Key and Add Repository​

To install MongoDB, you need to add its official APT repository.

  • Import the MongoDB GPG key to verify package authenticity:
sudo wget -qO - https://www.mongodb.org/static/pgp/server-4.4.asc | sudo apt-key add -

  • Add the MongoDB repository to your system’s APT sources:
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

  • Update package lists to include the MongoDB repository:
sudo apt-get update -y

Step 4: Install MongoDB​

Install MongoDB and its dependencies:

  • To install MongoDB, run:
sudo apt-get install mongodb-org -y

Step 5: Start MongoDB Service​

Once MongoDB is installed, start the service:

  • To start the MongoDB service and check its status, run:
sudo systemctl start mongod  
sudo systemctl status mongod

  • Enable MongoDB to start automatically at boot:
sudo systemctl enable mongod

Step 6: Verify MongoDB Installation​

To ensure MongoDB is installed and running correctly, check its version:

  • To check the MongoDB version, run:
sudo mongo --version

  • You can also launch the MongoDB shell:
sudo mongo

Step 7: Enable Replication in MongoDB Configuration​

Edit the MongoDB configuration file to enable replication.

  • Open the /etc/mongod.conf file on each server:
sudo vi /etc/mongod.conf
  • Change the bind IP address from 127.0.0.1 to 0.0.0.0 to allow MongoDB to listen on all interfaces:

Create a Mongo Key File on Each Server​

Step 8: Create Directory for Key Files​

To create a directory for MongoDB key files, run:

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

Step 9: Generate OpenSSL Key​

Run the following command to create a secure key file:

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

Step 10: Copy Key File to Other Servers​

Transfer the mongo-key file to the other servers using SFTP:

sftp root@your_IP_address

Enable Replication in MongoDB Configuration​

Step 11: Edit the MongoDB Configuration File​

Update the MongoDB configuration file on each server to enable security options:

sudo vi /etc/mongod.conf

Step 12: Add the Security Key​

Uncomment the security section and add the key configuration:

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

Set Permissions for the Key File​

Step 13: Configure File Permissions and Ownership​

Ensure the key file has the correct permissions and ownership:

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

Step 14: Stop the MongoDB Service​

Stop the MongoDB service before making further changes:

sudo systemctl stop mongod

Set Up Replication on All Nodes​

Step 15: Run MongoDB with Replication​

Execute the following command on all nodes to enable replication:

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

Step 16: Start the MongoDB Service​

Start the MongoDB service on all nodes:

sudo systemctl start mongod

Initialize the Replica Set and Add Members​

Step 17: Open the MongoDB Shell​

Access the MongoDB shell:

sudo mongo

Step 18: Initiate Replication​

Run the following command to initiate the replication process and add nodes:

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

​

Conclusion​

MongoDB is a robust, open-source NoSQL DBMS known for its flexibility and scalability, making it ideal for large-scale applications. By enabling replication, you ensure high availability and data redundancy across multiple servers.