How to create replica set in mongodb version 8.2

A replica set in MongoDB is a group of mongod instances that maintain the same data set, providing redundancy and high availability.

Step-by-Step Setup for MongoDB 8.2 Replica Set

We’ll use three nodes (members) for demonstration:

Node 1: localhost:27017 (Primary)
Node 2: localhost:27018 (Secondary)
Node 3: localhost:27019 (Secondary)

Step 1: Create Data Directories

On your system, create separate data folders for each instance:

mkdir C:\data\r1
mkdir C:\data\r2
mkdir C:\data\r3

(If on Linux/macOS)

mkdir -p /data/r1 /data/r2 /data/r3

Step 2: Start MongoDB Instances

Open three separate terminals (or command prompts).

Terminal 1 (Primary)

mongod --port 27017 --dbpath "C:\data\r1" --replSet "rs0"

Terminal 2 (Secondary 1)

mongod --port 27018 --dbpath "C:\data\r2" --replSet "rs0"

Terminal 3 (Secondary 2)

mongod --port 27019 --dbpath "C:\data\r3" --replSet "rs0"

✅ All must use the same replica set name (rs0 here).

Step 3: Connect to Mongo Shell (mongosh)

Open a new terminal and connect to the first node:

mongosh --port 27017

Step 4: Initialize the Replica Set

In the Mongo shell, run:

rs.initiate({
  _id: "rs0",
  members: [
    { _id: 0, host: "localhost:27017" },
    { _id: 1, host: "localhost:27018" },
    { _id: 2, host: "localhost:27019" }
  ]
})

Step 5: Verify Replica Set Status

Run:

rs.status()

✅ You should see:

• One PRIMARY
• Two SECONDARY nodes

Step 6: Test Replication

1. Connect to the Primary (port 27017).
2. Create a database and insert data: use testdb db.items.insertOne({ name: "replica test", time: new Date() })
3. Connect to a Secondary: mongosh --port 27018
4. Allow reading from secondary: db.getMongo().setReadPref('secondary') db.items.find() You’ll see the same document replicated

Optional: Run as Windows Services (MongoDB 8.2+)

If you want to run each instance as a Windows service:

1. Create 3 config files:
   • C:\Program Files\MongoDB\Server\8.2\bin\mongod1.cfg
   • C:\Program Files\MongoDB\Server\8.2\bin\mongod2.cfg
   • C:\Program Files\MongoDB\Server\8.2\bin\mongod3.cfg

Example config for node1:

systemLog:
  destination: file
  path: "C:\\data\\r1\\mongod.log"
storage:
  dbPath: "C:\\data\\r1"
net:
  bindIp: 127.0.0.1
  port: 27017
replication:
  replSetName: rs0

Then install each as a service:

mongod --config "C:\Program Files\MongoDB\Server\8.2\bin\mongod1.cfg" --install --serviceName "MongoDB1"
mongod --config "C:\Program Files\MongoDB\Server\8.2\bin\mongod2.cfg" --install --serviceName "MongoDB2"
mongod --config "C:\Program Files\MongoDB\Server\8.2\bin\mongod3.cfg" --install --serviceName "MongoDB3"

Then start:

net start MongoDB1
net start MongoDB2
net start MongoDB3

Done!

You now have a MongoDB 8.2 Replica Set running locally with:

• Automatic data replication
• High availability
• Failover support