# MongoDB Cross-Region Disaster Recovery (DR) on AWS EC2: Step-by-Step Guide

In today’s high-availability landscape, **disaster recovery (DR)** is more than a best practice—it's a requirement. This tutorial walks you through implementing a **cross-region MongoDB DR solution using EC2 instances with public IPs**. You’ll learn to replicate data between AWS regions to ensure business continuity even in regional outages.

---

## 🧭 Architecture Overview

The DR architecture consists of:

* A **primary MongoDB instance** running in one AWS region.
    
* A **replica set member** (secondary) in a separate AWS region.
    
* **Data replication** between these two nodes.
    

📌 *Diagram on page 1* shows a simple two-region EC2-based MongoDB setup with replication arrows connecting the nodes.

![](https://lh7-rt.googleusercontent.com/docsz/AD_4nXdmrTT9golye1yAWeI6kCSR3QpDxwRAjE2eZq4hM9-dFlQqZb_JNCJfwhn0idO4w2b9DUWh9NYFK_iZKTEVFwhqWDIBTGoXU-fXDHH3qNBW9wFKhlMTbqsl21-eCGa_KUexYQ9haA?key=7COqV19dSCUFk1rY8mZjBQ align="left")

---

## 🔧 Implementation Guide

### 1\. EC2 Instance Setup

* **Launch two Ubuntu EC2 instances**, one in each AWS region.
    
* **Security Groups** must allow:
    
    * Inbound traffic on **TCP port 27017** (MongoDB default port) from known IPs.
        

---

### 2\. Install MongoDB

Run these commands on both instances:

```bash
sudo apt-get install gnupg curl
curl -fsSL https://www.mongodb.org/static/pgp/server-8.0.asc | \
  sudo gpg -o /usr/share/keyrings/mongodb-server-8.0.gpg --dearmor

echo "deb [ arch=amd64,arm64 signed-by=/usr/share/keyrings/mongodb-server-8.0.gpg ] \
https://repo.mongodb.org/apt/ubuntu jammy/mongodb-org/8.0 multiverse" | \
sudo tee /etc/apt/sources.list.d/mongodb-org-8.0.list

sudo apt-get update
sudo apt-get install -y mongodb-org
sudo systemctl start mongod
sudo systemctl enable mongod
```

---

### 3\. Configure MongoDB

Edit the MongoDB config file on **both servers**:

```bash
sudo nano /etc/mongod.conf
```

Set the following values:

```bash
net:
  port: 27017
  bindIp: 0.0.0.0

replication:
  replSetName: "rs0"

security:
  authorization: enabled
```

Then restart the MongoDB service:

```bash
sudo systemctl restart mongod
```

---

### 4\. Initialize Replica Set

Log in to the Mongo shell on the **primary**:

```bash
mongosh
```

Run this setup:

```bash
rs.initiate({
  _id: "rs0",
  members: [
    { _id: 0, host: "primary-public-ip:27017", priority: 2 },
    { _id: 1, host: "secondary-public-ip:27017", priority: 1 }
  ]
})
```

Verify it using:

```bash
rs.status()
```

---

### 5\. Create Admin User

On the **primary**:

```bash
db.createUser({
  user: "adminUser",
  pwd: "securePassword",
  roles: [{ role: "root", db: "admin" }]
})
```

Reconnect with auth:

```bash
mongosh --host primary-public-ip:27017 -u adminUser -p securePassword --authenticationDatabase admin
```

---

### 6\. Test Replication

**Insert on primary**:

```bash
use testdb
db.testCollection.insertOne({ message: "Testing replication", timestamp: new Date() })
```

**Read from the secondary**:

```bash
mongosh --host secondary-public-ip:27017 -u adminUser -p securePassword --authenticationDatabase admin
```

Enable read preference:

```bash
db.getMongo().setReadPref("secondaryPreferred")
use testdb
db.testCollection.find()
```

---

### 7\. Simulate Failover

Stop MongoDB on the **primary**:

```bash
sudo systemctl stop mongod
```

Then, on the **secondary**, verify promotion:

```bash
rs.status()  // This node should now be PRIMARY
```

Bring the primary back:

```bash
sudo systemctl start mongod
```

---

📝 8. Checklist / TL;DR

Here’s a quick reference summary to validate your setup:

✅ EC2s launched in two AWS regions  
✅ MongoDB installed and configured  
✅ Replica set initialized  
✅ Authentication set up  
✅ Replication verified  
✅ Failover tested

## ✅ Conclusion

This guide demonstrates how to:

* Set up a **MongoDB replica set** across AWS regions.
    
* Secure it with authentication.
    
* Test real-time **replication and failover**.
    

While this is a basic manual setup, production deployments may benefit from:

* Private networking (e.g., VPC peering).
    
* Automation via Terraform or Ansible.
    
* Monitoring using MongoDB Ops Manager or Prometheus.