Create MongoDB Replicaset for Replication

Hello readers, today we are going to go through the MongoDB installation process in ubuntu. We will create three database servers and also create MongoDB replicaset between those three servers. Lets first look at installing the database. If you already installed database, move to replicaset section.

Although this tutorial is bit intense please stay focused. 🙂

Create MongoDB Database

I have taken the relevant steps from MongoDB official website. We are installing MongoDB version 3.2 Community Edition on Ubuntu 16.04.

Setting up the Server

First, lets import the public key to make sure that there is package consistency and authenticity in ubuntu package management tools. Use this command to import:
```
sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv EA312927
```
Download the appropriate version of MongoDB file based on your operating system. In my case, it is MongoDB 3.2 with Ubuntu 16.04. Use this command to download:
```
echo "deb http://repo.mongodb.org/apt/ubuntu xenial/mongodb-org/3.2 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-3.2.list
```
Update ubuntu package database using
```
sudo apt-get update
```

Install MongoDB packages using one of the two ways.

Install latest version using this command
```
sudo apt-get install -y mongodb-org
```

Or use this command to install a specific version, 3.2 in my case.

sudo apt-get install -y mongodb-org=3.2.20 mongodb-org-server=3.2.20 mongodb-org-shell=3.2.20 mongodb-org-mongos=3.2.20 mongodb-org-tools=3.2.20

In order for package management to NOT upgrade to latest releases of MongoDB, set a specific version using

echo "mongodb-org hold" | sudo dpkg --set-selections
echo "mongodb-org-server hold" | sudo dpkg --set-selections
echo "mongodb-org-shell hold" | sudo dpkg --set-selections
echo "mongodb-org-mongos hold" | sudo dpkg --set-selections
echo "mongodb-org-tools hold" | sudo dpkg --set-selections

For this tutorial, I am installing the three MongoDB servers on the same machine. This can be useful for use-cases like SIT and UAT. But for deploying in production purposes, you have to install each MongoDB server on a different physical server or virtual machine.

Create Required Files and Folders

Create a file /lib/systemd/system/mongod.service and copy the following content into it. If you are installing in three different machines then create this file in each of those servers.

[Unit]
Description=High-performance, schema-free document-oriented database
After=network.target
Documentation=https://docs.mongodb.org/manual

[Service]
User=mongodb
Group=mongodb
ExecStart=/usr/bin/mongod --quiet --config /etc/mongod.conf

[Install]
WantedBy=multi-user.target

If you are deploying it in single machine then create separate service file for each MongoDB server. Use the following commands to copy it 3 times.

sudo cp /lib/systemd/system/mongod.service /lib/systemd/system/mongod-24001.service
sudo cp /lib/systemd/system/mongod.service /lib/systemd/system/mongod-24002.service
sudo cp /lib/systemd/system/mongod.service /lib/systemd/system/mongod-24003.service

Create required folders for MongoDB. We have four root folders required. They are for config, data, logs and keys. In my case, I am creating all of my MongoDB related files in /home/cloudadmin/external-drive/mongodb folder. So you can change the path in the following commands based on your folder location. If you are deploying it in different machines you need to execute these commands in all of them except for db-24001, db-24002 and db-24003 folders. Create these folders in one server each.
```
sudo mkdir /home/cloudadmin/external-drive/mongodb
sudo mkdir /home/cloudadmin/external-drive/mongodb/config
sudo mkdir /home/cloudadmin/external-drive/mongodb/data
sudo mkdir /home/cloudadmin/external-drive/mongodb/data/db-24001
sudo mkdir /home/cloudadmin/external-drive/mongodb/data/db-24002
sudo mkdir /home/cloudadmin/external-drive/mongodb/data/db-24003
sudo mkdir /home/cloudadmin/external-drive/mongodb/logs
sudo mkdir /home/cloudadmin/external-drive/mongodb/keys
```

Make sure the folder is writeable using

sudo chmod go+w /home/cloudadmin/external-drive/mongodb

Create three configuration files for three mongo services using the following commands. If you are installing on three different machines then use each command on each of the system. Make sure to execute all commands with 24001 on one machine and similarly 24002, 24003 on respective machines.
```
sudo cp /etc/mongod.conf /home/cloudadmin/external-drive/mongodb/config/mongod-24001.conf
sudo cp /etc/mongod.conf /home/cloudadmin/external-drive/mongodb/config/mongod-24002.conf
sudo cp /etc/mongod.conf /home/cloudadmin/external-drive/mongodb/config/mongod-24003.conf
```

Now in /lib/systemd/system/mongod-24001.service change

ExecStart=/usr/bin/mongod --quiet --config /etc/mongod.conf

ExecStart=/usr/bin/mongod --quiet --config /home/cloudadmin/external-drive/mongodb/config/mongod-24001.conf

Similarly in /lib/systemd/system/mongod-24002.service change

ExecStart=/usr/bin/mongod --quiet --config /etc/mongod.conf

into

ExecStart=/usr/bin/mongod --quiet --config /home/cloudadmin/external-drive/mongodb/config/mongod-24002.conf

Likewise in /lib/systemd/system/mongod-24003.service change

ExecStart=/usr/bin/mongod --quiet --config /etc/mongod.conf

ExecStart=/usr/bin/mongod --quiet --config /home/cloudadmin/external-drive/mongodb/config/mongod-24003.conf

Change the configuration for first mongodb server in /home/cloudadmin/external-drive/mongodb/config/mongod-24001.conf. Change the following properties
- dbPath to </span/home/cloudadmin/external-drive/mongodb/data/db-24001
- path into /home/cloudadmin/external-drive/mongodb/logs/mongo-24001.log
- port to 24001
- bindIp into 0.0.0.0
Likewise for second mongodb server in /home/cloudadmin/external-drive/mongodb/config/mongod-24002.conf. Change the following properties
- dbPath to /home/cloudadmin/external-drive/mongodb/data/db-24002
- pathinto /home/cloudadmin/external-drive/mongodb/logs/mongo-24002.log
- port to 24002
- bindIp into 0.0.0.0
Similarly for third mongodb server in /home/cloudadmin/external-drive/mongodb/config/mongod-24003.conf. Change the following properties
- dbPath to /home/cloudadmin/external-drive/mongodb/data/db-24003
- path into /home/cloudadmin/external-drive/mongodb/logs/mongo-24003.log
- port to 24003
- bindIp into 0.0.0.0
Give permissions to MongoDB user and group using the following command
```
sudo chown -R mongodb:mongodb external-drive/mongodb/
```
If the logs, data and configurations are at different paths then you need to do this chown for each folder using the above command.

Start MongoDB Server

Execute the following commands to start each of the MongoDB servers.

sudo service mongod-24001 start
sudo service mongod-24002 start
sudo service mongod-24003 start

Setup MongoDB To Start On Reboot

If you want to start mongo instances on every time when the system reboots, enable them by using the following commands.

sudo su
systemctl enable /lib/systemd/system/mongod-24001.service
systemctl enable /lib/systemd/system/mongod-24002.service
systemctl enable /lib/systemd/system/mongod-24003.service

Now we have three MongoDB servers running on three different ports 24001, 24002 and 24003.

Create MongoDB Replicaset

Alright, so now we have deployed our MongoDB instances and they are up and running. But we haven’t created the replicaset yet. Also, we haven’t done the authentication and authorisation part as well. First we will look into creating replicaset without authentication and finally add authentication in the next section.

Note: If you are setting replicaset for a single MongodDB instance then check here.

1. Add replication settings to configuration files /home/cloudadmin/external-drive/mongodb/config/mongod-24001.conf, /home/cloudadmin/external-drive/mongodb/config/mongod-24002.conf, /home/cloudadmin/external-drive/mongodb/config/mongod-24003.conf
```
replication:
    oplogSizeMB: 10240
    replSetName: rssk
```
2. Restart all three servers using
```
sudo service mongod-24001 restart
sudo service mongod-24002 restart
sudo service mongod-24003 restart
```
3. Log in to one of the mongo servers. I am logging in the first server
```
mongo --port 24001
```
  Note: If you are unable to login, it might be because of locale settings. Use this command first before logging in.
```
export LC_ALL=C
```
4. Note: In the next 3 commands replace localhost with the IP address of the server.
5. In the mongo command line initiate replica-set using
```
rs.initiate({ _id: "rssk", members: [{ _id: 0, host: "localhost:24001" }] })
```
6. Then add the other 2 servers using
```
rs.add("localhost:24002");
rs.add("localhost:24003");
```
7. Check the server settings using
```
rs.conf()
```
  or
```
rs.status()
```
8. Now three mongo servers will replicate between each other. The replica set name is rssk but if you can change it, then you need to change it in the configuration as shown in the first step and restart.

Authentication & Authorisation

For authentication on replicaset, we should have a key. So lets create a key using
```
openssl rand -base64 756 > /home/cloudadmin/rssk.key
```
Note: Change the path to an existing directory
Move the newly created key to appropriate location
```
sudo mv rssk.key /home/cloudadmin/external-drive/mongodb/keys/rssk.key
```
Note: Change the path to your keys folder that you have created earlier
To protect file from accidental overwriting, we must change the file permissions using
```
sudo chmod 400 /home/cloudadmin/external-drive/mongodb/keys/rssk.key
```
Since MongoDB user will use it, we should give the user and group permissions to access it.
```
sudo chown -R mongodb:mongodb external-drive/mongodb/keys
```
Now lets start creating users for authentication. In order to do that lets login to our first database.
```
mongo --port 24001
```
Change to admin database using
```
use admin
```

In the mongo command create a user using

db.createUser({
   "user": "<dba username>", 
   "pwd": "<any password>", 
   "customData": { }, 
   "roles": [{
      "role": "clusterAdmin", 
      "db": "admin"
   }, { 
      "role": "dbAdminAnyDatabase", 
      "db": "admin" 
   }, { 
      "role" : "readWriteAnyDatabase", 
      "db" : "admin"
   }, {
      "role": "userAdminAnyDatabase", 
      "db" : "admin"
   }]
})

Note: Change the user and pwd values to the values that you like.

Add security settings to configuration files /home/cloudadmin/external-drive/mongodb/config/mongod-24001.conf, /home/cloudadmin/external-drive/mongodb/config/mongod-24002.conf, /home/cloudadmin/external-drive/mongodb/config/mongod-24003.conf
```
security:
    keyFile: /home/cloudadmin/external-drive/mongodb/keys/rssk.key
    authorization: enabled
    javascriptEnabled: false
```

Restart all three servers using

sudo service mongod-24001 restart
sudo service mongod-24002 restart
sudo service mongod-24003 restart

Now all three servers should have authentication.
If you want to set access to different databases and oplog then follow these additional steps.

If you are using a framework like Meteor then you might need to create an oplogger role and user.

mongo --port <primary-port-number> -u <username> -p <password> --authenticationDatabase admin

use admin

db.runCommand({ createRole: "oplogger", privileges: [{ resource: { db: 'local', collection: 'system.replset'}, actions: ['find']}, ], roles: [{role: 'read', db: 'local'}] })

db.createUser({ "user" : "oplogger", "pwd" : "<oplogger password>", "roles" : [ { "role" : "oplogger", "db" : "admin" }, { "role" : "read", "db" : "local" } ] })

Note: Change the pwd value to the values that you like.

Generate another user on a different database. Lets say luckyblogger

mongo --port <primary-port-number> -u <username> -p <password>

use luckyblogger

db.createUser({ "user" : "<username>", "pwd": "<password>", "customData" : {}, "roles" : [{ "role" : "readWrite", "db" : "luckyblogger" }] })

Note: Change the user and pwd values to the values that you like. You may also like to change the db value wherever necessary.

Create MongoDB Replicaset On One Server

In configuration file generally at /etc/mongodb.conf, uncomment the following lines. In the above tutorial, we have changed it to our config folder.
```
replSet=rs0
oplogSize=1024
```
Log in to database using mongo command. If you are using username and password, use the relevant mongo command to log in.
```
mongo
```
Switch to local database. After switching then initiate the replicaset using
```
use local
rs.initiate()
```

Now, you have replicaset available for your single instance.

Thats all. You are able to create a MongoDB replicaset with authentication on top of it. I hope you have enjoyed this tutorial. Thank you for reading my blog. Finally, please leave your feedback.

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Kishor Jami

He has over 9 years of experience in design, development and implementation of innovative business IT solutions. He is highly skilled in cloud computing, information management and application architecture. In free time, he writes some blogs and strives to learn new technical skills. Check out his recent blogs here.