How to Setup MongoDB Replication On Ubuntu 20.04

MongoDB is a free, open-source and document-oriented NoSQL database system developed by MongoDB Inc. It uses JSON-like documents with optional schemas instead of using tables and rows. It provides scalability and flexibility and allows you to store and retrieve large volume of data. MongoDB replica set is a group of processes used for redundancy and high availability. It allows you to distribute data across many database servers. In a replica set, one node is a primary node that receives all write operations while all others are secondary node that performs read operations.

In this post, we will show you how to set up three node MongoDB replication on Ubuntu 20.04.

Requirements

• Three server running Ubuntu 20.04.
• A root password is set up on your server.

Getting Started

First, you will need to set up a hostname resolution on each node so they can communicate with eachother using the hostname.

Edit the /etc/hosts file on each node and add the following lines:

nano /etc/hosts

Add the following lines:

node1-ip-address mongo-node1 node2-ip-address mongo-node2 node3-ip-address mongo-node3

Save and close the file then install all required dependencies on all nodes.

apt-get install dirmngr gnupg apt-transport-https ca-certificates software-properties-common -y

Once all the dependencies are installed, you can proceed to the next step.

Install MongoDB Server on All Nodes

Next, you will need to install MongoDB server on all nodes. By default, the latest version of MongoDB is not included in the Ubuntu default repository. So you will need to add the MongoDB repository on each node.

Run the following command to add the GPG key and MongoDB repository:

wget -qO - https://www.mongodb.org/static/pgp/server-4.4.asc | apt-key add - add-apt-repository 'deb [arch=amd64] https://repo.mongodb.org/apt/ubuntu focal/mongodb-org/4.4 multiverse'

Next, update the repository and install the MongoDB with the following command:

apt-get update -y apt-get install mongodb-org -y

Once the MongoDB is installed, start the MongoDB service and enable it to start at system reboot:

systemctl start mongod systemctl enable mongod

At this point, MongoDB is installed on all nodes.

Create an Admin User on Primary Node

Next, you will need to create an admin user on the primary node to authenticate MongoDB.

On the mongo-node1, connect to the MongoDB with the following command:

mongo

Once connected, change the database to admin with the following command:

use admin

Next, create a user named mongo-admin and set a password with the following command:

db.createUser({user: "mongo-admin", pwd: "password", roles:[{role: "root", db: "admin"}]})

Next, exit from the MongoDB with the following command:

exit

Configure Primary Node

First, you will need to create a key file for MongoDB on the primary node.

On the mongo-node1, run the following command to create a key file and set a proper permisssion and ownership:

openssl rand -base64 756 > /opt/mongo-keyfile chmod 400 /opt/mongo-keyfile chown mongodb:mongodb /opt/mongo-keyfile

Next, copy the /opt/mongo-keyfile file to second and third node.

scp /opt/mongo-keyfile root@mongo-node2:/opt/ scp /opt/mongo-keyfile root@mongo-node3:/opt/

Next, edit the MongoDB main configuration file on mongo-node1:

nano /etc/mongod.conf

Add / Change the following lines:

net: port: 27017 bindIp: 127.0.0.1,node1-ip-address security: keyFile: /opt/mongo-keyfile replication: replSetName: "replica01"

Save and close the file when you are finished.

Configure Second and Third Node

Next, you will need to configure the second and third MongoDB node.

On the mongo-node2, edit the MongoDB main configuration file:

nano /etc/mongod.conf

Add / Change the following lines:

net: port: 27017 bindIp: 127.0.0.1,node2-ip-address security: keyFile: /opt/mongo-keyfile replication: replSetName: "replica01"

Save and close the file then set proper ownership and permission to the mongo-key file:

chmod 400 /opt/mongo-keyfile chown mongodb:mongodb /opt/mongo-keyfile

On the mongo-node3, edit the MongoDB main configuration file:

nano /etc/mongod.conf

Add / Change the following lines:

net: port: 27017 bindIp: 127.0.0.1,node3-ip-address security: keyFile: /opt/mongo-keyfile replication: replSetName: "replica01"

Save and close the file then set proper ownership and permission to the mongo-key file:

chmod 400 /opt/mongo-keyfile chown mongodb:mongodb /opt/mongo-keyfile

At this point, all nodes are configured.

Restart MongoDB Service on All Nodes

Next, you will need to restart the MongoDB service on all nodes one by one.

On the mongo-node1, restart the MongoDB service using the following command:

systemctl restart mongod

On the mongo-node2, restart the MongoDB service using the following command:

systemctl restart mongod

On the mongo-node3, restart the MongoDB service using the following command:

systemctl restart mongod

Start Replication and Add Members

Next, you will need to start the replication on the primary node and other nodes as a member node.

On the mongo-node1, connect to the Mongo with admin user:

mongo -u mongo-admin -p --authenticationDatabase admin

Next, initiate the replica set with the following command:

> rs.initiate()

Output:

{ "info2" : "no configuration specified. Using a default configuration for the set", "me" : "node1-ip-address:27017", "ok" : 1 }

Next, add mongo-node2 as a member with the following command:

replica01:PRIMARY> rs.add("mongo-node2")

Output:

{ "ok" : 1, "$clusterTime" : { "clusterTime" : Timestamp(1619609840, 1), "signature" : { "hash" : BinData(0,"zuOCVWO9Nv7q+4sceYaXd9x/7kw="), "keyId" : NumberLong("6956170826928357380") } }, "operationTime" : Timestamp(1619609840, 1) }

Next, add mongo-node3 as a member with the following command:

replica01:PRIMARY> rs.add("mongo-node3")

Output:

{ "ok" : 1, "$clusterTime" : { "clusterTime" : Timestamp(1619609869, 1), "signature" : { "hash" : BinData(0,"FIUN74frDell2yfOAN6qzZAIljE="), "keyId" : NumberLong("6956170826928357380") } }, "operationTime" : Timestamp(1619609869, 1) }

You can also check the status of all node with the following command;

rs.status()

Test Replication

At this point, replication is configured on the primary node. Now, its time to test whether the replication is working or not.

On the mongo-node1, create a database and add some values.

mongo -u mongo-admin -p --authenticationDatabase admin 
replica01:PRIMARY> use exampleDB 
replica01:PRIMARY> for (var i = 0; i <= 10; i++) db.exampleCollection.insert( { x : i } )

Output:

WriteResult({ "nInserted" : 10 })

Now, check your database with the following command:

replica01:PRIMARY> show dbs

Output:

admin 0.000GB 
config 0.000GB 
exampleDB 0.000GB 
local 0.000GB

On the mongo-node2, connect to the Mongo shell with the following command:

mongo -u mongo-admin -p --authenticationDatabase admin

Once connected, run the following command to enable secondary member read operations on a per-connection basis

replica01:SECONDARY> db.getMongo().setSecondaryOk()

Next, change the database to exampleDB:

replica01:SECONDARY> use exampleDB

Next, run the following command to show all documents:

replica01:SECONDARY> db.exampleCollection.find()

If replication is working, you’ll see a list of the sample documents we created on the primary host.

{ "_id" : ObjectId("60894e33213113780d5fef3b"), "x" : 0 } { "_id" : ObjectId("60894e33213113780d5fef3c"), "x" : 1 } { "_id" : ObjectId("60894e33213113780d5fef3d"), "x" : 2 } { "_id" : ObjectId("60894e33213113780d5fef40"), "x" : 5 } { "_id" : ObjectId("60894e33213113780d5fef42"), "x" : 7 } { "_id" : ObjectId("60894e33213113780d5fef3f"), "x" : 4 } { "_id" : ObjectId("60894e33213113780d5fef43"), "x" : 8 } { "_id" : ObjectId("60894e33213113780d5fef44"), "x" : 9 } { "_id" : ObjectId("60894e33213113780d5fef3e"), "x" : 3 } { "_id" : ObjectId("60894e33213113780d5fef45"), "x" : 10 } { "_id" : ObjectId("60894e33213113780d5fef41"), "x" : 6 }

Conclusion

In the above guide, you learned how to configure MongoDB replication on Ubuntu 20.04. You can now add more members to the replica set. I hope this guide will help you to distribute data across many database servers in the production environment.

credits: https://snapshooter.com/learn/mongodb/mongo_replication