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kaustubh yerkade
kaustubh yerkade

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Plan of Action: MongoDB 8.0 - 3 Node Replica Set on Air-Gapped RHEL 8.9

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🧾 Plan of Action: MongoDB 8.0 - 3 Node Replica Set on Air-Gapped RHEL 8.9

📘 Overview

  • Goal: Setup a MongoDB 8.0 replica set with 3 RHEL 8.9 air-gapped servers
  • Nodes: 3 (Primary, Secondary, Secondary/Arbiter)
  • No Internet access on servers
  • RPMs and config provided from an internet-enabled Windows machine

🧱 Architecture

Node Hostname Role
1 mongo-node1 Primary
2 mongo-node2 Secondary
3 mongo-node3 Secondary

🔹 1. Prerequisites on All RHEL Servers

  • RHEL 8.9 installed
  • Static IP or /etc/hosts updated for inter-node resolution
  • Ports open: 27017/tcp
  • SELinux set to permissive or configured
  • Firewall open: 
  sudo firewall-cmd --add-port=27017/tcp --permanent
  sudo firewall-cmd --reload
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🔹 2. On Windows Machine (with Internet)

A. Download Required RPMs for MongoDB 8.0

  1. Visit: https://repo.mongodb.org/yum/redhat/8/mongodb-org/8.0/x86_64/RPMS/

  2. Download:

    • mongodb-org-8.0.0-1.el8.x86_64.rpm
    • mongodb-org-server-8.0.0-1.el8.x86_64.rpm
    • mongodb-org-shell-8.0.0-1.el8.x86_64.rpm
    • mongodb-org-mongos-8.0.0-1.el8.x86_64.rpm
    • mongodb-org-tools-8.0.0-1.el8.x86_64.rpm

  3. Place RPMs in a folder: mongodb8-rpms/

  4. Zip the folder: mongodb8-rpms.zip

🔹 3. Transfer to All 3 RHEL Servers

  • Use winSCP to move mongodb8-rpms.zip to each server.
  • On each node: 
  unzip mongodb8-rpms.zip -d mongodb8-rpms
  cd mongodb8-rpms
  sudo dnf install *.rpm
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🔹 4. Configure MongoDB on Each Node

Edit /etc/mongod.conf:

net:
  bindIp: 0.0.0.0
  port: 27017

replication:
  replSetName: rs0
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Update /etc/hosts:

<IP1> mongo-node1
<IP2> mongo-node2
<IP3> mongo-node3
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🔹 5. Start MongoDB on Each Node 

sudo systemctl enable mongod
sudo systemctl start mongod
sudo systemctl status mongod
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🔹 6. Initiate Replica Set (on Primary Node) 

mongosh
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rs.initiate({
  _id: "rs0",
  members: [
    { _id: 0, host: "mongo-node1:27017" },
    { _id: 1, host: "mongo-node2:27017" },
    { _id: 2, host: "mongo-node3:27017" }
  ]
})
rs.status()
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🔹 7. (Optional) Enable Authentication

On primary node:

use admin
db.createUser({
  user: "admin",
  pwd: "securePassword",
  roles: [ { role: "root", db: "admin" } ]
})
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Edit /etc/mongod.conf:

security:
  authorization: enabled
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Restart MongoDB:

sudo systemctl restart mongod
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🔁 Optional: Local Yum Repo 

sudo dnf install createrepo -y
createrepo /tmp/mongodb8-rpms
sudo tee /etc/yum.repos.d/mongodb-local.repo <<EOF
[mongodb-local]
name=MongoDB 8 Local Repo
baseurl=file:///tmp/mongodb8-rpms
enabled=1
gpgcheck=0
EOF
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✅ Final Checklist

Task Check
Mongo running systemctl status mongod
Replica configured rs.status()
Authentication works db.auth('admin', 'securePassword')
Network open telnet mongo-nodeX 27017

📄 MongoDB Cluster Cheat Sheet (Replica Set)

🔧 Basic Cluster Setup Commands

▶️ Initialize Replica Set (run on primary)

rs.initiate({
_id: "rs0",
members: [
{ _id: 0, host: "mongo-node1:27017" },
{ _id: 1, host: "mongo-node2:27017" },
{ _id: 2, host: "mongo-node3:27017" }
]
})

➕ Add Node 

rs.add("mongo-node4:27017")
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❌ Remove Node 

rs.remove("mongo-node3:27017")
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⛑️ Step Down Primary 

rs.stepDown()
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📊 Monitoring & Config

🧠 Show Config 

rs.conf()
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📈 Status of Replica Set 

rs.status()
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⏱️ Replication Lag Info (Secondary) 

rs.printSlaveReplicationInfo()
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🔐 Authentication

👤 Create Admin User 

use admin
db.createUser({
  user: "admin",
  pwd: "securePassword",
  roles: [ { role: "root", db: "admin" } ]
})
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🔒 Enable Authentication in mongod.conf 

security:
  authorization: enabled
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💡 CRUD Commands (Data Ops)

📥 Insert 

use mydb
db.users.insertOne({ name: "Ragu", role: "admin" })
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📤 Read 

db.users.find()
db.users.findOne({ name: "Ragu" })
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🔁 Update 

db.users.updateOne({ name: "Ragu" }, { $set: { role: "engineer" } })
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🗑️ Delete 

db.users.deleteOne({ name: "Ragu" })
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⚙️ Connection Commands

▶️ Local Shell 

mongosh
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▶️ Remote Shell (no auth) 

mongosh --host mongo-node1:27017
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▶️ Remote Shell (with auth) 

mongosh "mongodb://admin:securePassword@mongo-node1:27017/?authSource=admin&replicaSet=rs0"
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📁 File Paths

File Location
Config /etc/mongod.conf
Logs /var/log/mongodb/mongod.log
Data /var/lib/mongo

🧪 Testing Tips

  • Shut down primary: sudo systemctl stop mongod
  • Watch failover with: rs.status()
  • Restart with: sudo systemctl start mongod

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