MongoDB Replica Set Setup Example for MOCM Distributed Mode

Info

This is an example setup for deploying a MongoDB 8.x Replica Set for MOCM Distributed Mode. Adapt the values (IPs, ports, paths, credentials) to match your environment. For detailed MongoDB installation, refer to the official documentation links below

1. Prerequisites

1.1 Environment Requirements

Component	Requirement
MongoDB Version	8.0.x (Community or Enterprise)
Number of Nodes	3 (minimum for production)
Supported OS	RHEL 8/9, Rocky Linux 8/9, Ubuntu 22.04/24.04, Windows Server 2019/2022
RAM	Minimum 16 GB per node (32 GB recommended)
Disk	Minimum 100 GB free space (SSD recommended)
Network	All nodes must communicate on TCP port 27017

1.2 Hostname Planning

Role	IP (example)
Primary	10.40.160.159
Secondary	10.40.160.160
Secondary	10.40.160.161

MongoDB 5.0+ IP Address Note

Starting from MongoDB 5.0, nodes configured with only IP addresses fail startup validation by default. To use IP addresses without DNS hostnames, you must add the following startup parameter in mongod.conf / mongod.cfg:

setParameter:

disableSplitHorizonIPCheck: true

This parameter is included in the configuration in Section 5.

2. Install MongoDB 8.x

Perform on ALL 3 nodes

Follow the official MongoDB installation guide for your operating system.

Operating System	Official Installation Guide
RHEL / Rocky Linux	https://www.mongodb.com/docs/manual/tutorial/install-mongodb-on-red-hat/
Ubuntu	https://www.mongodb.com/docs/manual/tutorial/install-mongodb-on-ubuntu/
Windows	https://www.mongodb.com/docs/manual/tutorial/install-mongodb-on-windows/

After installation, do not start the MongoDB service yet. Proceed to configure TLS and keyfile first.

3. Generate TLS Certificate

Info

Perform on one machine, then distribute to all nodes. If your organization already has a PKI/CA infrastructure, use your existing CA to sign the MongoDB server certificates. Skip to Step 3.2.

3.1 Create Certificate Authority (CA]

mkdir -p /etc/mongodb/ssl && cd /etc/mongodb/ssl

# Generate CA key and certificate (valid 10 years)

openssl genrsa -out ca.key 4096

openssl req -new -x509 -days 3650 -key ca.key -out ca.crt \

-subj "/C=US/ST=California/L=SanFrancisco/O=YourOrganization/OU=IT/CN=MongoDB-CA"

3.2 Generate Server Certificate (per node]

Repeat for each node (mongo1, mongo2, mongo3), replacing values:

# Example for node 10.40.160.159

openssl genrsa -out mongo1.key 4096

openssl req -new -key mongo1.key -out mongo1.csr \

-subj "/C=US/ST=California/L=SanFrancisco/O=YourOrganization/OU=MongoDB/CN=10.40.160.159"

# SAN extension (REQUIRED - must include IP)

cat > mongo1-ext.cnf <<EOF

[v3_req]

subjectAltName = @alt_names

[alt_names]

IP.1 = 10.40.160.159

EOF

# Sign with CA

openssl x509 -req -in mongo1.csr -CA ca.crt -CAkey ca.key \

-CAcreateserial -out mongo1.crt -days 3650 \

-extensions v3_req -extfile mongo1-ext.cnf

# Create PEM (key + cert combined - required by MongoDB)

cat mongo1.key mongo1.crt > mongo1.pem

Repeat for other nodes

Replace mongo1 with mongo2/mongo3 and update the IP value:

mongo2: 10.40.160.160
mongo3: 10.40.160.161

3.3 Distribute Certificates

File	Copy to
ca.crt	All 3 nodes
mongo1.pem	mongo1 only
mongo2.pem	mongo2 only
mongo3.pem	mongo3 only

Certificate directory:

Linux: /etc/mongodb/ssl/
Windows: C:\MongoDB\ssl\

Set permissions (Linux):

sudo chown -R mongod:mongod /etc/mongodb/ssl/

sudo chmod 600 /etc/mongodb/ssl/*.pem /etc/mongodb/ssl/*.key

sudo chmod 644 /etc/mongodb/ssl/ca.crt

4. Generate Keyfile for Internal Authentication

# Generate (on one node)

openssl rand -base64 756 > mongodb-keyfile

Copy the same keyfile to all 3 nodes:

Linux: /etc/mongodb/ssl/mongodb-keyfile (chmod 400, owned by mongod)
Windows: C:\MongoDB\ssl\mongodb-keyfile

# Linux - set permissions

sudo chmod 400 /etc/mongodb/ssl/mongodb-keyfile

sudo chown mongod:mongod /etc/mongodb/ssl/mongodb-keyfile

5. Configure MongoDB (mongod.conf / mongod.cfg)

This is the critical configuration specific to MOCM deployment. Apply on all 3 nodes.

5.1 Linux Configuration

# /etc/mongod.conf

storage:

dbPath: /var/lib/mongo

systemLog:

destination: file

logAppend: true

path: /var/log/mongodb/mongod.log

net:

port: 27017

bindIp: 0.0.0.0

tls:

mode: requireTLS

certificateKeyFile: /etc/mongodb/ssl/mongo1.pem

CAFile: /etc/mongodb/ssl/ca.crt

allowConnectionsWithoutCertificates: true

security:

keyFile: /etc/mongodb/ssl/mongodb-keyfile

authorization: enabled

replication:

replSetName: "rs0"

setParameter:

disableSplitHorizonIPCheck: true

processManagement:

timeZoneInfo: /usr/share/zoneinfo

5.2 Windows Configuration

# C:\Program Files\MongoDB\Server\8.0\bin\mongod.cfg

storage:

dbPath: C:\MongoDB\data

systemLog:

destination: file

logAppend: true

path: C:\MongoDB\log\mongod.log

net:

port: 27017

bindIp: 0.0.0.0

tls:

mode: requireTLS

certificateKeyFile: C:\MongoDB\ssl\mongo1.pem

CAFile: C:\MongoDB\ssl\ca.crt

allowConnectionsWithoutCertificates: true

security:

keyFile: C:\MongoDB\ssl\mongodb-keyfile

authorization: enabled

replication:

replSetName: "rs0"

setParameter:

disableSplitHorizonIPCheck: true

5.3 Key Configuration Parameters

Parameter	Value	Description
net.tls.mode	requireTLS	All connections must use TLS
net.tls.allowConnectionsWithoutCertificates	true	Clients don't need client cert (set false for mutual TLS)
security.keyFile	path to keyfile	Internal authentication between replica set members
security.authorization	enabled	Enforce role-based access control
replication.replSetName	rs0	Must be identical on all nodes
setParameter.disableSplitHorizonIPCheck	true	Required when using IP addresses instead of hostnames
net.bindIp	0.0.0.0	Listen on all interfaces

6. Start MongoDB and Initialize Replica Set

6.1 Start Service on All Nodes

# Linux

sudo systemctl enable mongod

sudo systemctl start mongod

sudo systemctl status mongod

# Windows

# If service config was updated, reinstall service first:

& "C:\Program Files\MongoDB\Server\8.0\bin\mongod.exe" --remove

& "C:\Program Files\MongoDB\Server\8.0\bin\mongod.exe" --config "C:\Program Files\MongoDB\Server\8.0\bin\mongod.cfg" --install --serviceName "MongoDB"

Start-Service MongoDB

6.2 Initialize Replica Set

Connect to 10.40.160.159 using mongosh with TLS:

mongosh --host 10.40.160.159 --port 27017 \

--tls --tlsCAFile /etc/mongodb/ssl/ca.crt \

--tlsCertificateKeyFile /etc/mongodb/ssl/mongo1.pem

Run:

rs.initiate({

_id: "rs0",

members: [

{ _id: 0, host: "10.40.160.159:27017" },

{ _id: 1, host: "10.40.160.160:27017" },

{ _id: 2, host: "10.40.160.161:27017" }

]

})

6.3 Verify

rs.status()

Expected: 1 PRIMARY + 2 SECONDARY

7. Create Users for MOCM

Warning

Create users immediately after rs.initiate(). The localhost exception closes after the first user is created.

Connect to the PRIMARY node and run:

// Create Admin User

use admin

db.createUser({

user: "adminUser",

pwd: "CHANGE_ME_STRONG_PASSWORD",

roles: [

{ role: "userAdminAnyDatabase", db: "admin" },

{ role: "clusterAdmin", db: "admin" },

{ role: "readWriteAnyDatabase", db: "admin" }

]

})

8. Connection String for MOCM

GUI "Database Address" Field

10.40.160.159:27017,10.40.160.160:27017,10.40.160.161:27017

9. Configure MOCM Installer - Database Configuration

After MongoDB Replica Set is ready, enter the following values in the "My OPSWAT Central Management Setup" installer:

Field	Value
Database Address	10.40.160.159:27017,10.40.160.160:27017,10.40.160.161:27017
Connection Type	Discovery
Database Admin Username	The admin user created in Step 7
Password	The admin password created in Step 7

Issue	Solution
Service fails to start	Check logs: `/var/log/mongodb/mongod.log` or `C:\MongoDB\log\mongod.log`
Keyfile permission error (Linux)	`chmod 400` and `chown mongod:mongod`
TLS handshake failure	Verify SAN in cert matches hostname in rs.initiate()
Members can't connect	Check firewall, verify hostname resolution between nodes
"not authorized"	Ensure you created users before localhost exception closed

9.3 Useful Command

rs.status() // Replica set health

rs.conf() // Current replica set config

db.serverStatus() // Server metrics

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MongoDB Replica Set Setup Example for MOCM Distributed Mode

1. Prerequisites

1.1 Environment Requirements

1.2 Hostname Planning

2. Install MongoDB 8.x

3. Generate TLS Certificate

3.1 Create Certificate Authority (CA]

3.2 Generate Server Certificate (per node]

3.3 Distribute Certificates

4. Generate Keyfile for Internal Authentication

5. Configure MongoDB (mongod.conf / mongod.cfg)

5.1 Linux Configuration

5.2 Windows Configuration

5.3 Key Configuration Parameters

6. Start MongoDB and Initialize Replica Set

6.1 Start Service on All Nodes

6.2 Initialize Replica Set

6.3 Verify

7. Create Users for MOCM

8. Connection String for MOCM

9. Configure MOCM Installer - Database Configuration

9. Verification & Troubleshooting

9.1 Test Connection

9.2 Common Issues

9.3 Useful Command