How to Set Up MongoDB Master‑Slave Replication on CentOS: A Step‑by‑Step Guide

MongoDB Introduction

MongoDB is an open‑source document‑oriented NoSQL database that stores data in JSON‑like documents, offering high flexibility, scalability, powerful query language, aggregation framework, and support for various programming languages.

MongoDB Features

Document‑oriented data model with flexible schema.

Distributed architecture with automatic sharding.

High‑performance read/write operations.

Rich query language including aggregation pipelines, geospatial queries, and full‑text search.

Dynamic schema changes and easy extensibility.

Horizontal scalability by adding more servers.

Visual management tools such as MongoDB Compass.

MongoDB Master‑Slave Replication Overview

MongoDB Master‑Slave Replication

Replication synchronizes data from a primary node to multiple secondary nodes, improving reliability and availability. The primary handles write operations, while secondaries handle reads. In case of primary failure, an eligible secondary is automatically elected as the new primary, ensuring high availability.

MongoDB Replica Set

A replica set is a group of mongod instances that maintain the same data set.

It provides redundancy and high availability; a minimum of three members (one primary, one secondary, one arbiter or another secondary) is recommended.

If the primary fails, the remaining members hold an election to select a new primary.

Practice Overview

Practice Environment Planning

hostname   IP address   OS version   MongoDB version   Role
master    192.168.3.141   centos 7.9   v5.0.21   Primary
node01    192.168.3.142   centos 7.9   v5.0.21   Secondary
node02    192.168.3.143   centos 7.9   v5.0.21   Secondary

Practice Introduction

1. Prepare three CentOS 7.9 servers. 2. This is a personal test environment; use caution in production. 3. The main goal is to configure MongoDB master‑slave replication.

Install MongoDB

Installation Instructions

All three servers must follow the steps below to install MongoDB.

vim /etc/yum.repos.d/mongodb.repo

[mongodb-org]
name=MongoDB Repository
baseurl=https://mirrors.tuna.tsinghua.edu.cn/mongodb/yum/el7/
gpgcheck=0
enabled=1

Check YUM repository status

Check the status of YUM repository mirrors.

# yum repolist all | grep enable
base/7/x86_64         CentOS-7 - Base - mirrors.aliyun.com       enabled: 10072
extras/7/x86_64       CentOS-7 - Extras - mirrors.aliyun.com     enabled: 518
mongodb-org/7         MongoDB Repository                         enabled: 337
updates/7/x86_64      CentOS-7 - Updates - mirrors.aliyun.com    enabled: 5176

Install MongoDB

Install MongoDB directly using yum.

yum install -y mongodb-org-server mongodb-org

Modify bound IP

Change the bindIp in /etc/mongod.conf to 0.0.0.0.

vim /etc/mongod.conf

Start MongoDB service

Start and enable MongoDB service.

systemctl start mongod.service && systemctl enable mongod.service

Check MongoDB service status

Verify that the MongoDB service is running.

# systemctl status mongod
● mongod.service - MongoDB Database Server
   Loaded: loaded (/usr/lib/systemd/system/mongod.service; enabled; vendor preset: disabled)
   Active: active (running) since Wed 2023-09-13 16:38:48 CST; 44s ago
   Docs: https://docs.mongodb.org/manual
   Main PID: 1472 (mongod)
   CGroup: /system.slice/mongod.service
           └─1472 /usr/bin/mongod -f /etc/mongod.conf

Check MongoDB version

Display the installed MongoDB version.

# mongod --version
db version v5.0.21
Build Info: {
    "version": "5.0.21",
    "gitVersion": "4fad44a858d8ee2d642566fc8872ef410f6534e4",
    "openSSLVersion": "OpenSSL 1.0.1e-fips 11 Feb 2013",
    "modules": [],
    "allocator": "tcmalloc",
    "environment": {
        "distmod": "rhel70",
        "distarch": "x86_64",
        "target_arch": "x86_64"
    }
}

Master Node Configuration

Enter MongoDB shell

Open the MongoDB shell locally.

mongo

Create admin user

Create an administrator account named admin .

db.createUser({
  user: "admin",
  pwd: "admin",
  roles: [{role: "userAdminAnyDatabase", db: "admin"}]
})

Create test user

Authenticate with the admin account and create a test user.

use admin;
db.auth("admin","admin")

Create a user huawei with the root role.

db.createUser({
  user: "huawei",
  pwd: "huawei",
  roles: ["root"]
})

Access test database

Connect to MongoDB using the admin credentials.

mongo -uadmin -padmin --authenticationDatabase admin

Create key file on master

Generate a key file for internal authentication.

mkdir -p /data/mongodb/
openssl rand -base64 666 > /data/mongodb/mongodb.key

Create the same directory on the two secondary nodes.

mkdir -p /data/mongodb/

Copy key file

Transfer the key file to both secondary nodes.

scp /data/mongodb/mongodb.key [email protected]:/data/mongodb/
scp /data/mongodb/mongodb.key [email protected]:/data/mongodb/

All Nodes Configuration

Configuration instructions

Execute the following commands on all three nodes.

Directory and file permissions

Set ownership and permissions for the data directory and key file.

chown mongod:mongod -R /data/mongodb/
chmod 600 /data/mongodb/mongodb.key

Edit /etc/mongod.conf

Update the configuration file on each node.

systemLog:
  destination: file
  logAppend: true
  path: /var/log/mongodb/mongod.log
storage:
  dbPath: /var/lib/mongo
  journal:
    enabled: true
processManagement:
  fork: true
  pidFilePath: /var/run/mongodb/mongod.pid
  timeZoneInfo: /usr/share/zoneinfo
net:
  port: 27017
  bindIp: 0.0.0.0
security:
  authorization: enabled
  keyFile: /data/mongodb/mongodb.key
  clusterAuthMode: keyFile
replication:
  replSetName: rs0
  oplogSizeMB: 5000

Restart MongoDB service

Restart the MongoDB service on all nodes.

systemctl restart mongod

Configure MongoDB Replication

User authentication

Connect to the primary node.

mongo

Authenticate with the huawei account.

use admin;
db.auth("huawei","huawei")

Configure replica set

Initialize the replica set with one primary and two secondaries.

rs.initiate({
   _id: "rs0",
   members: [
      { _id: 0, host: "192.168.3.141:27017" },
      { _id: 1, host: "192.168.3.142:27017" },
      { _id: 2, host: "192.168.3.143:27017" }
   ]
})

Check replica set configuration

Authenticate again and view the replica set configuration.

use admin;
db.auth("huawei","huawei")
rs.config()

Check replica set status

Display the current status of the replica set.

rs.status()

Determine primary node

Identify which host is the primary.

rs.isMaster()

Test MongoDB Failover

Stop primary MongoDB service

Stop the MongoDB service on the primary node.

systemctl stop mongod.service

Check slave status

Log into a secondary node and verify it has become the new primary.

mongo