Configure MongoDB 4.4 replica set on Ubuntu 20.04 | 18.04 | 16.04

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In this guide, I will show you how to configure MongoDB replica set on Ubuntu 20.04 | 18.04 | 16.04 server. MongoDB is an enterprise-level NoSQL database system with automatic expansion, high availability and high performance. In NoSQL databases, data is stored in the document structure using MongoDB BSON format. You cannot use SQL statements to insert or retrieve data in MongoDB.

What is MongoDB replication/replica set?

In MongoDB, a replica set is a group of mongod processes that maintain the same data set. Replica sets are the foundation of all production deployments because they provide data redundancy and high availability.

This tutorial will cover the steps required to create a valid three-node replica set without configuring access control to restrict access. This guide is based on the following system IP addresses:

MongoDB Server1: 10.10.5.2
MongoDB Server2: 10.10.5.3
MongoDB Server3: 10.10.5.4

Step 1: Set requirements

Before configuring the replica set, you must install MongoDB on all servers. Ensure that the correct hostname is configured on the server used for replication.

If you do not have an available DNS server, please set the mapping between IP address and FQDN locally on the server.

# Edit and set the values correctly
10.10.5.2 mongodb-01.example.net mongodb-01
10.10.5.3 mongodb-02.example.net mongodb-02
10.10.5.4 mongodb-03.example.net mongodb-03

Step 2: Install MongoDB on all Ubuntu 20.04 | 18.04 nodes

Please follow the steps below to install MongoDB on the Ubuntu server.

Update system:

sudo apt-get update
sudo apt-get upgrade && sudo reboot

Import MongoDB public GPG key:

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 9DA31620334BD75D9DCB49F368818C72E52529D4

After importing the key, add the repository:

### Ubuntu 20.04 ###
echo "deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu focal/mongodb-org/4.4 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-4.4.list

### Ubuntu 18.04 ###
echo "deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.4 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-4.4.list

### Ubuntu 16.04 ###
echo "deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu xenial/mongodb-org/4.4 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-4.4.list

Install MongoDB package

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

Use a dedicated disk to store MongoDB data (optional)

For my setup, I have 10GB Specially used for auxiliary storage of MongoDB data.I partitioned it and installed it to /data/mongodb.

# lsblk 
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda      8:0    0   32G  0 disk 
|-sda1   8:1    0  487M  0 part /boot
|-sda2   8:2    0  1.9G  0 part [SWAP]
`-sda3   8:3    0 29.6G  0 part /
vda      252:0  0 10G    0 disk

Create a GPT partition table for the secondary disk, it can be multiple disks

parted -s -a optimal -- /dev/vda mklabel gpt
parted -s -a optimal -- /dev/vda mkpart primary 0% 100%
parted -s -- /dev/vda align-check optimal 1

Then create the LVM volume, which will make it easy to extend the partition

$ sudo pvcreate  /dev/vda1
  Physical volume "/dev/vda1" successfully created.

$ sudo vgcreate vg11 /dev/vda1
  Volume group "vg11" successfully created

$ sudo lvcreate -n data -l 100%FREE vg11
Logical volume "data" created

Create ext4The file system created on the logical volume.

$ sudo mkfs.ext4 /dev/mapper/vg11-data
mke2fs 1.44.1 (24-Mar-2018)
Creating filesystem with 2620416 4k blocks and 655360 inodes
Filesystem UUID: b98e07e5-1b04-4282-a9db-fa5b73c74d2f
Superblock backups stored on blocks: 
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632

Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (16384 blocks): done
Writing superblocks and filesystem accounting information: done

Create mount point and mount partition

echo "/dev/mapper/vg11-data /data ext4 defaults 0 0" | sudo tee -a /etc/fstab
mkdir /data
mount -a

Confirm that the partition is installed successfully:

$ df -hT | grep /data
/dev/mapper/vg11-data ext4      9.8G   37M  9.3G   1% /data

Create a folder for MongoDB data

sudo mkdir /data/mongodb
sudo chown -R mongodb:mongodb /data/mongodb
sudo chmod -R 775 /data/mongodb

Configure the storage path to the storage path previously created on all nodes

$ sudo vim /etc/mongod.conf
# Where and how to store data.
storage:
  dbPath: /data/mongodb
  journal:
    enabled: true

Step 3: Configure MongoDB replica set

Now that we have prepared all the necessary things, let’s proceed to configure the MongoDB replica set.

Change MongoDB listening address from local IP on all nodes

$ sudo vim /etc/mongod.conf
# node 1
# network interfaces
net:
  port: 27017
  bindIp: 10.10.5.2  # Listen to local interface only, comment to listen on all interfaces.

# node 2
# network interfaces
net:
  port: 27017
  bindIp: 10.10.5.3  # Listen to local interface only, comment to listen on all interfaces.

# node 3
# network interfaces
net:
  port: 27017
  bindIp: 10.10.5.4  # Listen to local interface only, comment to listen on all interfaces.

Configure MongoDB replica set

One of the MongoDB nodes starts with PRIMARY, All other nodes will be SECONDARY.Data is always PRIMARY Node, then copy the data set to all other nodes SECONDARYnode.

Edit the MongoDB configuration file mongod.conf and enable replica sets on all nodes

replication:
  replSetName: "replica01"

Open port 27017/tcp On the firewall:

sudo ufw enable
sudo ufw allow ssh
sudo ufw allow 27017/tcp

Configure MongoDB to start during OS boot

sudo systemctl enable mongod.service
sudo systemctl restart mongod.service

Check the listening address of the MongoDB service:

# ss -tunelp | grep -i mongo
tcp   LISTEN  0       128                10.10.5.2:27017          0.0.0.0:*      users:(("mongod",pid=15288,fd=11)) uid:111 ino:46927 sk:4 <->

Start MongoDB replica set

Our MongoDB Node1 (mongodb-01)will be PRIMARY And the other two will act as SECONDARY

$ mongo 10.10.5.2
MongoDB shell version v4.0.1
connecting to: mongodb://10.10.5.2:27017/test
MongoDB server version: 4.0.1
Welcome to the MongoDB shell.
For interactive help, type "help".
...
>

Initialize the replica set node1 By running the following command:

> rs.initiate()
{
        "info2" : "no configuration specified. Using a default configuration for the set",                                                           
        "me" : "10.10.5.2:27017",
        "ok" : 1,
        "operationTime" : Timestamp(1534797235, 1),
        "$clusterTime" : {
                "clusterTime" : Timestamp(1534797235, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),                                                                          
                        "keyId" : NumberLong(0)
                }
        }
}

Make sure you get 1 for ok State

Add secondary node

replica01:PRIMARY> rs.add("mongodb-02")
{
        "ok" : 1,
        "operationTime" : Timestamp(1534797580, 1),
        "$clusterTime" : {
                "clusterTime" : Timestamp(1534797580, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        }
}

replica01:PRIMARY> rs.add("mongodb-03")
{
        "ok" : 1,
        "operationTime" : Timestamp(1534797614, 1),
        "$clusterTime" : {
                "clusterTime" : Timestamp(1534797614, 1),
                "signature" : {
                        "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
                        "keyId" : NumberLong(0)
                }
        }
}

Use the following command to check the status of the replica set:

replica01:PRIMARY> rs.status()

Check the status of the master station

replica01:PRIMARY> rs.isMaster()

Test MongoDB replication

Create a test database on mongodb-01

replica01:PRIMARY> use test_db
switched to db test_db

Add some data

> db.test.save(
{
    "desc": "My Test Database",
    "apps":  ["Test1", "Test2", "Test3", "Test4"],
})

replica01:PRIMARY> show dbs
admin    0.000GB
config   0.000GB
local    0.000GB
test_db  0.000GB
replica01:PRIMARY> use test_db
switched to db test_db
replica01:PRIMARY> show collections
test

in conclusion

Now you have valid MongoDB replication.You can increase the cluster size from three nodes to Fives node Seven Nodes or more. This number is calculated according to the following formula: [Master Eligible Nodes) / 2 + 1], Which means that high availability requires an odd number of nodes, the minimum number is three.

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