Linux VPS MongoDB Replica Set Tutorial: Complete Setup with Authentication and Failover on Ubuntu 24.04 in 2026

Understanding MongoDB Replica Sets for Production VPS Hosting

A MongoDB replica set provides automatic failover and data redundancy across multiple VPS instances. Unlike standalone MongoDB installations, replica sets maintain synchronized copies of your data across multiple nodes. This ensures zero data loss during hardware failures or maintenance windows.

The architecture is straightforward. A primary node handles all write operations while secondary nodes replicate data from the primary.

When the primary fails, the remaining nodes automatically elect a new primary within seconds.

This tutorial walks through setting up a three-node replica set on Ubuntu 24.04 VPS instances. You'll configure authentication, enable SSL connections, and implement monitoring for production-ready reliability.

Prerequisites and VPS Requirements

You need three Ubuntu 24.04 VPS instances with at least 2GB RAM and 20GB storage each. Enable private networking for secure inter-node communication.

Open these ports in your firewall:

• 27017 (MongoDB default port)
• 22 (SSH access)

Each VPS needs a static IP address and proper hostname resolution. Configure your /etc/hosts file on all nodes:

192.168.1.10 mongo-primary
192.168.1.11 mongo-secondary1
192.168.1.12 mongo-secondary2

The HostMyCode VPS platform provides private networking and flexible firewall configuration. This makes it ideal for multi-node database deployments.

Installing MongoDB 7.0 on All VPS Nodes

Install MongoDB 7.0 on each VPS node using the official repository. Run these commands on all three servers:

curl -fsSL https://www.mongodb.org/static/pgp/server-7.0.asc | sudo gpg --dearmor -o /usr/share/keyrings/mongodb-server-7.0.gpg

echo "deb [ arch=amd64,arm64 signed-by=/usr/share/keyrings/mongodb-server-7.0.gpg ] https://repo.mongodb.org/apt/ubuntu jammy/mongodb-org/7.0 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-7.0.list

sudo apt update
sudo apt install -y mongodb-org

Prevent automatic updates that could break your replica set:

echo "mongodb-org hold" | sudo dpkg --set-selections
echo "mongodb-org-database hold" | sudo dpkg --set-selections
echo "mongodb-org-server hold" | sudo dpkg --set-selections
echo "mongodb-mongosh hold" | sudo dpkg --set-selections
echo "mongodb-org-mongos hold" | sudo dpkg --set-selections
echo "mongodb-org-tools hold" | sudo dpkg --set-selections

Create the MongoDB data directory and set proper permissions:

sudo mkdir -p /var/lib/mongodb
sudo chown mongodb:mongodb /var/lib/mongodb
sudo chmod 755 /var/lib/mongodb

Configuring MongoDB Replica Set Operation

Edit the MongoDB configuration file on each node. The primary difference between nodes will be the hostname binding.

On the primary node (mongo-primary), edit /etc/mongod.conf:

storage:
  dbPath: /var/lib/mongodb
  journal:
    enabled: true

systemLog:
  destination: file
  logAppend: true
  path: /var/log/mongodb/mongod.log
  logRotate: rename

net:
  port: 27017
  bindIp: 127.0.0.1,192.168.1.10

processManagement:
  timeZoneInfo: /usr/share/zoneinfo

security:
  authorization: enabled
  keyFile: /etc/mongodb-keyfile

replication:
  replSetName: "rs0"

On secondary nodes, only change the bindIp address to match each server's private IP.

Use 192.168.1.11 for mongo-secondary1 and 192.168.1.12 for mongo-secondary2.

Setting Up Authentication and Security

Generate a keyfile for inter-node authentication. Run this on the primary node:

sudo openssl rand -base64 756 > /tmp/mongodb-keyfile
sudo mv /tmp/mongodb-keyfile /etc/mongodb-keyfile
sudo chmod 400 /etc/mongodb-keyfile
sudo chown mongodb:mongodb /etc/mongodb-keyfile

Copy the keyfile to all secondary nodes using scp:

scp /etc/mongodb-keyfile user@mongo-secondary1:/tmp/
scp /etc/mongodb-keyfile user@mongo-secondary2:/tmp/

On each secondary node, move the keyfile to the correct location:

sudo mv /tmp/mongodb-keyfile /etc/mongodb-keyfile
sudo chmod 400 /etc/mongodb-keyfile
sudo chown mongodb:mongodb /etc/mongodb-keyfile

For SSL configuration, reference our SSL certificate management guide. This shows how to secure MongoDB connections with Let's Encrypt certificates.

Initializing the MongoDB Replica Set

Start MongoDB on all nodes without authentication first:

sudo systemctl start mongod
sudo systemctl enable mongod

Connect to the primary node and initialize the replica set. Comment out the keyFile line in /etc/mongod.conf temporarily:

mongosh --host mongo-primary:27017

Run the replica set initialization command:

rs.initiate({
  _id: "rs0",
  members: [
    { _id: 0, host: "mongo-primary:27017", priority: 2 },
    { _id: 1, host: "mongo-secondary1:27017", priority: 1 },
    { _id: 2, host: "mongo-secondary2:27017", priority: 1 }
  ]
})

Wait for the replica set to initialize. Check the status:

rs.status()

Create an administrative user while still connected to the primary:

use admin
db.createUser({
  user: "admin",
  pwd: "your-strong-password",
  roles: [ { role: "root", db: "admin" } ]
})

Enabling Authentication and Testing Failover

Uncomment the keyFile line in /etc/mongod.conf on all nodes and restart MongoDB:

sudo systemctl restart mongod

Test authentication by connecting with credentials:

mongosh --host mongo-primary:27017 -u admin -p

Verify all nodes are communicating properly:

rs.status()

Test automatic failover by stopping MongoDB on the primary:

sudo systemctl stop mongod

Connect to a secondary node and verify it becomes primary within 12 seconds:

mongosh --host mongo-secondary1:27017 -u admin -p
rs.status()

Start the original primary back up. It will rejoin as a secondary automatically.

Monitoring and Maintenance Best Practices

Set up MongoDB logs rotation to prevent disk space issues:

sudo logrotate -f /etc/logrotate.d/mongodb-server

Monitor replica set health with these commands:

# Check replica set configuration
rs.conf()

# Monitor replication lag
rs.printSlaveReplicationInfo()

# Check oplog size
db.oplog.rs.stats()

Enable MongoDB's built-in monitoring:

db.enableFreeMonitoring()

For production environments, integrate with external monitoring solutions. Our VPS monitoring guide covers Prometheus and Grafana setup for database metrics.

Common Issues and Troubleshooting

If nodes can't communicate, check firewall rules and network connectivity:

# Test connectivity between nodes
telnet mongo-secondary1 27017

When authentication fails, verify keyfile permissions and contents are identical on all nodes:

sudo ls -la /etc/mongodb-keyfile
sudo md5sum /etc/mongodb-keyfile

For split-brain scenarios, check network partitions. Ensure you have an odd number of voting members.

Monitor disk space regularly. MongoDB requires significant space for oplog and journaling:

df -h /var/lib/mongodb

Frequently Asked Questions

Can I add more nodes to my replica set later?

Yes, you can add additional secondary nodes using rs.add("hostname:27017"). The maximum recommended replica set size is 50 members, with up to 7 voting members.

How much replication lag is acceptable in production?

Replication lag under 1 second is ideal for most applications. Monitor this with rs.printSlaveReplicationInfo() and investigate if lag exceeds 10 seconds consistently.

What happens if all secondary nodes fail?

The primary can continue accepting writes but cannot acknowledge them with write concern "majority". The primary will step down if it loses contact with a majority of replica set members.

Should I run replica set nodes on the same VPS provider?

For high availability, distribute nodes across different availability zones or data centers. HostMyCode offers VPS locations in multiple regions for geographic redundancy.

How do I backup a replica set?

Use mongodump against a secondary node to avoid impacting primary performance. You can also use filesystem snapshots if your VPS provider supports consistent point-in-time snapshots.