# 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 $(lsb_release -sc)/mongodb-org/4.4 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-4.4.list
```
After executing this command, refresh your server’s local package index to ensure APT can locate the MongoDB-org package:
```
sudo apt-get update -y
```
### **Install MongoDB**
Now, you can install MongoDB using the following command:
```
sudo apt-get install mongodb-org -y
```
This command will install the MongoDB package and its dependencies.
### **Start MongoDB Service**
After installing MongoDB, it should start automatically. To check the service status, run:
```
sudo systemctl start mongod
sudo systemctl status mongod
```
#### Enable MongoDB to Start on the Boot
```
sudo systemctl enable mongod
```
#### Verify Installation
To verify that MongoDB is installed successfully, open the MongoDB shell by following these steps:
sudo mongo --version
```
sudo mongo
```
## **Enable Replication in Each Server's**
#### **MongoDB Configuration File:-**
You have successfully configured the **/etc/hosts** file on your servers to map hostnames to their respective IP addresses.
To change MongoDB settings, edit the primary configuration file found at **/etc/mongod.conf**. This file is created automatically during installation.
Use a text editor **vi** to open and modify the file. Here’s the command:
```
sudo vi /etc/mongod.conf
```
In MongoDB, various configuration options allow you to customize the server's behavior. The **system log** option manages the database’s logging settings, enabling you to specify what gets logged and where. Conversely, the **net** option is essential for configuring network-related settings, providing control over parameters such as port configuration and network interfaces.
Update the IP address in each server from 127.0.0.0 to 0.0.0.0.
Create a mongo key file in each server
```
sudo mkdir -p /etc/mongodb/key-files/
```
Now create an OpenSSL and run these commands
Copy these mongo-key files in another 2 vms
**$ 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.
