How to create and start a MongoDB Replica Set?

This guide is primarily for Windows PC. However you might find some useful information on replica sets here.

Step 1: Initial Setup - Create necessary folders

Create the 3 folders for PRIMARY(1) and SECONDARY(2) MongoD instances

• C:\data\db0
• C:\data\db1
• C:\data\db2

Step 2: Configure MongoD

I will be using MONGO_DIR to alias the MongoDB installation folder. For example MONGO_DIR equals to C:\Program Files\MongoDB\Server\4.4 on my PC

Open the file MONGO_DIR\bin\mongod.cfg in your favorite editor. And check if there are any replication options confiured. By default you will find replication commented.

#replication:

You can specify replSetName as rs0

replication:
 replSetName: rs0

I recommend you to run the following commands with administrator privilages. You might need to open 4 terminals or command prompt windows(all as administrator). (Optional)I recommend using Microsoft Terminal in which you can open new terminal as a new tab - easy to manage.

Step 3: Start PRIMARY node

Run the following command to start a PRIMARY mongod instance

mongod --port 27017 --replSet rs0 --dbpath="C:\data\db0"

Step 4: Start your first SECONDARY node

Open new command prompt window. Run the following command to start a SECONDARY mongod instance

mongod --port 27027 --replSet rs0 --dbpath="C:\data\db1"

Step 5: Start another SECONDARY node

Open new command prompt window. Run the following command to start another SECONDARY mongod instance

mongod --port 27037 --replSet rs0 --dbpath="C:\data\db2"

Step 6: Initiate Replica Set

Open new command prompt window and connect to primary node

mongo --port 27017

Initiate Replica Set

rs.initiate()

Step 7: Add new members to Replica Set

In the same window where you initiated the replica set, Run the following commands:

rs.add( { host: "127.0.0.1:27027", priority: 0, votes: 0 } )
rs.add( { host: "127.0.0.1:27037", priority: 0, votes: 0 } )

Now we have one primary node and two secondary nodes in the replica set. We can confirm it by running the following command:

rs.status()

Bonus: Connecting through MongoDB Compass

You can use the following connection string to connect using Compass

mongodb://127.0.0.1:27017/?replicaSet=rs0&w=majority&readPreference=primary&ssl=false

Last Updated on Dec 30, 2020