The cluster environment

A cluster in informatics is understood as the union of different components of hardware or software that work together as if it were a single one. In this case, our objective will be that the databases that we make in the first node, automatically, are replicated in the second.

For it, I will use in both nodes the following configuration:

Node 1:

OS: Debian 10 Buster
Hostname: osradar1
IP address: 192.168.250.100
RAM Memory: 512 mb
Hard drive: 20gb

Node 2:

OS: Debian 10 Buster
Hostname: osradar2
IP address: 192.168.250.101
RAM Memory: 512 mb
Hard drive: 20gb

So we can get started.

Installing MariaDB Galera Cluster

To make a cluster with MariaDB it is necessary to install Galera cluster. However, from the most recent versions of MariaDB, this utility is incorporated into the main server package. Therefore, there is nothing strange to do. We will take this opportunity to install a necessary package such as rsync.

It is necessary that your user is able to execute commands with sudo, if not, read our tutorial to enable it.

Read, How to enable sudo on Debian 10?

Once you’ve done that, we can start with the installation:

:~$ sudo apt install rsync mariadb-server mariadb-client

This process has to be done in both nodes.

Configure the MariaDB cluster

Now it is necessary to configure a little the cluster so that the nodes can communicate between them. In the first node, you have to edit the file /etc/mysql/mariadb.conf.d/50-server.cnf and modify some things.

:~$ sudo nano /etc/mysql/mariadb.conf.d/50-server.cnf

And add the following:

[galera]
wsrep_on=ON
wsrep_provider=/usr/lib/galera/libgalera_smm.so
wsrep_cluster_address="gcomm://"
binlog_format=row
default_storage_engine=InnoDB
innodb_autoinc_lock_mode=2
bind-address=0.0.0.0
wsrep_cluster_name="galera_cluster"
wsrep_node_address="db1"
wsrep_node_name="osradar1"

The following must be edited within this text file:

wsrep_cluster_address="gcomm://[NODE1_IP_ADDRESS,NODE2_IP_ADDRESS..]"

For example:

wsrep_cluster_address="gcomm://192.168.250.100,192.168.250.101"

Further down in the same file you have to edit the node configuration:

wsrep_node_address="192.168.250.100"
wsrep_node_name="osradar1"

Then save the changes and close the file.

In node2, in the same configuration file, the changes would be as follows:

wsrep_cluster_address="gcomm://192.168.250.100,192.168.250.101"

And:

wsrep_node_address="192.168.250.101"
wsrep_node_name="osradar2"

In both nodes, a root password must be defined for MariaDB. You can do this with the following command:

:~$ sudo mysql_secure_installation

If you use a firewall, then you need to open the following ports:

• 3306/tcp
• 4444/tcp
• 4567/tcp
• 4568/tcp
• 4567/udp

This has to be done in both nodes.

Initializing and testing the cluster

Now we can initialize the cluster. To do this, stop the MariaDB service in both nodes:

:~$ sudo systemctl stop mariadb

Then, at the first node, start the cluster with the following command:

:~$ sudo galera_new_cluster

Once you start it, you won’t see a screen output. But if you check the status of the cluster, you will notice that it already recognizes the first node:

:~$ sudo mysql -u root -p -e "SHOW STATUS LIKE 'wsrep_cluster_size'"

At the second node, start the MariaDB service:

:~$ sudo systemctl start mariadb

With this, the second node will be automatically added to the cluster. To check it, just execute this command in the first node:

:~$ sudo mysql -u root -p -e "SHOW STATUS LIKE 'wsrep_cluster_size'"

And now we’ll see that this is the second node added.

To test the cluster just create a database in the first node and see how it automatically replicates in the second:

:~$ sudo mysql -u root -p
> SHOW DATABASES;
> CREATE DATABASE example;

In the second node:

:~$ sudo mysql -u root -p
> SHOW DATABASES;

This way you can easily create a MariaDB cluster on Debian 10.

Conclusion

A MariaDB cluster can be created in Debian 10, quite simply. Since the application incorporates it in the same package. Just install it and make some configurations.

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Pacemaker is an open source cluster manager software that achieves maximum high availability of your services.

Corosync Cluster Engine is an open source project derived from the OpenAIS project under new BSD License. It’s a group communication system with additional features for implementing High Availability within applications.

Prerequisites

1. Two or more CentOS Servers
2. Each server must have unique IP address
3. At leat one Floating IP Address
4. Root Privileges

Our Working Environment
host1 192.168.130.141
host2 192.168.130.142
host3 192.168.130.143
Floating IP Address 192.168.130.222

Run step 1 to step 3 on all servers host1, host2 and host3

Step 1: Configure Host File

Edit the host file on each server in order to map the hostname of all servers. login to each server (host1, host2 and host3) one by one and run below commands.

vi /etc/hosts

and add below configurations.

192.168.130.141 host1
192.168.130.142 host2
192.168.130.141 host3

Save changes and exit

Now test the hosts’ configuration using below commands.

ping -c 2 host1
ping -c 2 host2
ping -c 2 host3

Make sure ‘host1’, ‘host2’ and ‘host3’ are mapped to correct IP addresses.

Step 2: Install Nginx

Run below commands on host1, host2 and host3 to install nginx web server.

yum install epel-release -y
yum install nginx -y

After installation, set the default index.html page on each server.

##Run below Command on host1
echo '<h1>host1 - osradar.com</h1>' > /usr/share/nginx/html/index.html

##Run below Command on host2
echo '<h1>host2 - osradar.com</h1>' > /usr/share/nginx/html/index.html

##Run below Command on host3
echo '<h1>host3 - osradar.com</h1>' > /usr/share/nginx/html/index.html

Step 3: Installation and configuration of Pacemaker, Corosync, and Pcsd

Run below commands on each server to install Pacemaker, Corosync, and Pcsd

yum install corosync pacemaker pcs -y

Then run below commands on each server to enable all services to launch automatically at system boot.

systemctl enable pacemaker
systemctl enable corosync
systemctl enable pcsd

Now start the pcsd Pacemaker command line interface on all servers.

systemctl start pcsd

Now set a new password for ‘hacluster’ user password must be same for all servers. This user has been created automatically during software installation.

RUn below command to all servers and set same password.

passwd hacluster

High Availability software have been installed on to the system.

Step 4: Create and Configure Cluster

Note: Run steps 4 to step 7 on “host1” only.

We will create a new cluster with 3 servers.

we need to authorize all servers to create new cluster using below command. username will be “hacluster”

pcs cluster auth host1 host2 host3

Now create the cluster named osradar_cluster for all servers using below command.

pcs cluster setup --name osradar_cluster host1 host2 host3

Now start and enable all cluster services using below command.

pcs cluster start --all
pcs cluster enable --all

Now verify the cluster status.

pcs status cluster

Step 5: Disable STONITH and Ignore the Quorum Policy

Since we are running three node cluster and don’t have a fencing device. So we have to disable the STONITH setting but it is not recommended for production environment.

Disable STONITH and ignore Quorum policy using below commands.

pcs property set stonith-enabled=false
pcs property set no-quorum-policy=ignore

Then make sure stonith and the quorum policy are disabled.

pcs property list

Step 6: Add the Floating IP and Resources

Floating IP is the IP address that wil be migrated/moved automatically from one server to another server. Our floating ip address wil be 192.168.130.222 then we will add two resources, the Floating IP address resource with the name ‘virtual_ip’ and a new resource for the Nginx web server named ‘webserver’

Run below command to add floating IP address ‘virtual_ip’

pcs resource create virtual_ip ocf:heartbeat:IPaddr2 ip=192.168.130.222 cidr_netmask=32 op monitor interval=30s

Then run below command to add a new resource for the Nginx ‘webserver’

pcs resource create webserver ocf:heartbeat:nginx configfile=/etc/nginx/nginx.conf op monitor timeout="5s" interval="5s"

Now verify resources status and check that there is no error.

pcs status resources

Step 7: Add Constraint Rules to the Cluster

Now will configure High Availability Rules and resource constraint.

Set the collation constraint for webserver and virtual_ip resources with the score ‘INFINITY’ using below command.

pcs constraint colocation add webserver virtual_ip INFINITY

Now Set the ‘virtual_ip’ and ‘webserver’ resources always on same node servers using below command.

pcs constraint order virtual_ip then webserver

Next, stop and start the cluster

pcs cluster stop --all
pcs cluster start --all

Now again verify resources status.

pcs status resources

You can sse that virtual_ip and webserver resources started on the same server/node ‘host2’

Step 8: Configure Firewalld

Run below commands to add necessary services in firewalld.

firewall-cmd --add-service=high-availability --permanent 
firewall-cmd --add-service=http --permanent 
firewall-cmd --add-service=https --permanent

Now reload the firewalld

firewall-cmd --reload

Step 9: Testing

In this step, we will Test the node status, corosync members and status and then test the high-availability of the Nginx webserver by accessing the Floating IP address.

Test node status corosync members and corosync status using below command.

pcs status nodes
corosync-cmapctl | grep members
pcs status corosync

Finally, check the webserver High Availability. Open your web browser and type the Floating IP address 192.168.130.222

You will see the web page from the ‘host2’ server.

Now, stop the cluster on the ‘host2’ server using below command.

pcs cluster stop host2 --force

And check again the page and this time, you will see the page from the ‘host1’ server as below.

You have installed Nginx webserver High Availability with Pacemaker, Corosync, and Pcsd on CentOS 7 server successfully.

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Most of the GlusterFS functionalities are implemented as translators, including:

• Mirroring and file replication.
• Fragmentation of the files or Data striping.
• Load balancing for reading and writing files.
• Fault tolerant volumes.
• I/O planning and disk caching.
• The storage quotas.

In this tutorial, we will cluster using GlusterFS between two server machines that are using CentOS 7

0.- Requeriments

To make this turtorial we will use three computers with GNU/LINUX systems, must have at least 1gb of ram and use 64bits systems, also a separate hard disk in /dev/sdb.

Server 1:

• Hostname: gluster1.osradar.local
• O.S:  CentOS 7
• Memory: 1gb
• Ip Address: 192.168.1.9
• Disk: 8gb /dev/sdb

Server 2:

• Hostname: gluster2.osradar.local
• O.S:  CentOS 7
• Memory: 1gb
• Ip Address: 192.168.1.10
• Disk: 8gb /dev/sdb

1.- Configuring DNS (both nodes)

This first step is vital because GlusterFS uses name resolution to communicate between servers and clients. As root user you write to a terminal:

:~# nano /etc/hosts

And in the file it places the information of the nodes in the following way:

192.168.1.9 gluster1.osradar.local gluster1
192.168.1.10 gluster2.osradar.local gluster2

2.- Installing GlusterFS (both nodes)

To install Gluster we need to add its repository first, to do this, in a terminal we must write:

:~# yum install centos-release-gluster

When the package installation is complete, the repository will be added and we can now install GlusterFS.

:~# yum install glusterfs-server

Once the installation is complete, we can start the service:

:~# systemctl start glusterd
:~# systemctl enable glusterd

The next thing to do is to modify the firewall settings:

:~# firewall-cmd --zone=public --add-rich-rule='rule family="ipv4" source address="IP_ADDRESS_HERE" accept'
:~# firewall-cmd --reload

3.-Add a storage (both nodes)

Now we must prepare the second hard disk (/dev/sdb) to be used as a brick (basic storage unit in Gluster). We’ll do a partition there.

:~# fdisk /dev/sdb

To perform the process properly, write the options in this order

Command (m for help): n
Select (default p): p
Partition number (1-4, default 1): 1
press enter
press enter
Command (m for help): p
Command (m for help): w

now we proceed to format the partition:

:~# mkfs.ext4 /dev/sdb1

Then we create a folder and mount the partition on it.

:~# mkdir -p /data/glusterfs
:~# mount /dev/sdb1 /data/glusterfs

We make sure that the partition is automatically mounted at system boot:

:~# echo "/dev/sdb1 /data/glusterfs ext4 defaults 0 0" | tee --append /etc/fstab

4.-Configuring GlusterFS

The next step will be on node 1. tell Gluster that node 2 is trustworthy to build the cluster itself. To do this we must execute the following command:

:~# gluster peer probe gluster2.osradar.local

And then we verify that the other node has been added correctly with these commands:

:~# gluster peer status
:~# gluster pool list

5.- Creating GlusterFS Volume

We create a folder on both nodes that will serve as the volume folder:

:~# mkdir -p /data/glusterfs/glustervolume

We now proceed to create the volume by indicating that you will use two mirrors in this case:

:~# gluster volume create glusterfsvolumne replica 2 gluster1.osradar.local:/data/glusterfs/glustervolume gluster2.osradar.local:/data/glusterfs/glustervolume

We start the volume:

:~# gluster volume start glusterfsvolumne

The installation and configuration of glusterfs on a server is now complete. We proceed to install the client on another machine.

GlusterFS client

Now it is the customer’s turn to use another CentOS 7 device with an IP address of 192.168.1.7. The other features of the device do not influence the use of the device.

We proceed to install the glusterfs-client package:

:~# yum install glusterfs-client

Once the installation is finished, we will create a folder to mount the volume.

:~# mkdir -p /mnt/glusterfsvolumne

we set up the firewall:

:~# firewall-cmd --zone=public --add-rich-rule='rule family="ipv4" source address="192.168.1.7" accept'
:~# ffirewall-cmd --reload

And we mount the previously created glusterFs volume.

:~# mount -t glusterfs gluster1.osradar.local:/glusterfsvolumne /mnt/glusterfsvolumne

We checked the mounting:

df -hP /mnt/glusterfsvolumne/

we add the entry in fstab so that it is automatically mounted:

:~# echo "gluster1.osradar.local:/glusterfsvolumne /mnt/glusterfsvolumne/ glusterfs  defaults,_netdev 0 0" | tee --append /etc/fstab

Testing the replication

First of all, in the server nodes, we execute the following commands:

On the first node (gluster1.osradar.local):

:~# mount -t glusterfs gluster2.osradar.local:/glusterfsvolumne /mnt

On second node (gluster2.osradar.local):

:~# mount -t glusterfs gluster1.osradar.local:/glusterfsvolumne /mnt

On client machine:

First we create the files, and verify

:~# touch /mnt/glusterfsvolumne/filetest{1..4}
:~# ls /mnt/glusterfsvolumne

Now from node 1 we show the files created from the client.

:~# ls -l /mnt/

That concludes the article and I hope it has served you well. Remember that for everything to work, you have to be careful with the firewall and define its rules correctly.

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DRBD is a software that allows you to replicate the data of a partition between several machines. which is excellent for always having a backup of the information.

Installing DRBD

1.-Installing DRBD packages on both server

The first thing to do is to install DRDB on both nodes. To do this it is necessary to enable an external repository called ELRepo where we will download the necessary packages. We need to be root user, so open a terminal and type sudo -i, enter your password and we’ll have admin permissions.

:~# sudo -i

Now we proceed to enable the repository:

:~# rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org

We install it:

:~# rpm -Uvh http://www.elrepo.org/elrepo-release-7.0-3.el7.elrepo.noarch.rpm

With the repository added, we can now install the DRBD packages.

:~# yum install drbd90-utils kmod-drbd90

After the installation of the packages is finished, make sure that the drbd module is loaded to the kernel. We do it with the following command:

:~# lsmod | grep -i drbd

In this case, we notice that it was not loaded, to solve this, we execute these two commands.

:~# echo drbd > /etc/modules-load.d/drbd.conf
:~# modprobe drbd

The first one makes the module load at the beginning of the system and the second one enables it for the active session. We proceed to check again and we’ll get:

2.- Configure DRBD

Once the packages are installed correctly, we must modify their configuration. First we’ll back up the original file. We will do this on both nodes:

:~# mv /etc/drbd.d/global_common.conf /etc/drbd.d/global_common.conf.bak

Once the initial configuration file is backed up, we will create a new one:

:~# nano /etc/drbd.d/global_common.conf

And we’ll put the following in it:

global {
 usage-count no;
}
common {
 net {
  protocol C;
 }
}

Next we will create a new file for the new resource that will be drbd1 in this case. The file will be called drbd1.res.

:~# nano /etc/drbd.d/drbd1.res

We will add the following:

resource drbd1 {
        disk /dev/sdb;
        device /dev/drbd1;
        meta-disk internal;
        on osradar {
                address 192.168.1.9:7789;
        }
	on osradar2 {
                address 192.168.1.12:7789;
        }
}

We briefly explain: disk refers to the hard disk to be replicated, device to the partition inside the disk, in the on segment comes the hostname of the computers; address to the ip address of the node and 7789 is the port where they will communicate.

The next step is to initialize and create the resource at each of the nodes.

:~# drbdadm create-md drbd1

Later we enable the drbd daemon on both nodes:

:~# systemctl start drbd
:~# systemctl enable drbd

Now let’s define who the primary node will be, in our case it will be in “osradar”, that is, the first node.

:~# drbdadm down drbd1
:~# drbdadm up drbd1

On the second node:

:~# drbdadm down drbd1
:~# drbdadm up drbd1

In case an error occurs setting the primary node, you can use this command:

:~# drbdadm primary drbd1 --force

Next we must configure the firewall to accept connections through the drbd port.

:~# firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="192.168.1.12" port port="7789" protocol="tcp" accept

Remember to modify the address in each node: if you are in node1 then in the command you must put the ip of node2.

and reboot the firewall:

:~# firewall-cmd --reload

We’ll have a DRBD cluster up and running, and we’ll be able to make changes to the first node’s partition and replicate from the network to the second one.

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One of the technologies available to perform this task is clustering. In short, cluster is a group of multiple computers linked by a high-speed network, so that the whole is seen as a single computer, more powerful than common desktop computers.

The advantages of having servers in clusters are many and range from processing speed to database scalability, allowing database replication.

MariaDB has within its products a software that allows us to do this in an efficient way on Ubuntu 18.04 and that utility is called MariaDB Galera Cluster. In this tutorial we will learn how to make one with two nodes.

Information about the nodes

For this article we will make a cluster with two nodes with the following data:

• OS: Ubuntu Server 18.04
• Hostnames: osradar1, osradar2
• IP address: 192.168.250.6, 192.168.250.7
• RAM Memory: 512mb both
• Hard Drive: 20gb

It is vital to handle this information before we start our work because we will have to handle it well later on.

Installing MariaDB Galera Cluster

As the official documentation tells us, from version 10.1 the utility is self-contained, inside the mariadb-server package. Therefore we proceed to install it:

              sudo -i

When you enter the password, you will be a root user.

Now, we proceed to install the mariadb server and mariadb galera cluster.

             apt install mariadb-server mariadb-client

Then we proceed to install rsync which is a necessary utility for the cluster to work.

             apt install rsync

Note: these commands must be executed on each of the nodes

Configuring MariaDB cluster

In order for the cluster to achieve communication between the nodes, a common configuration file must be created in each of them. We create it with the following command:

              nano /etc/mysql/conf.d/cluster.cnf

And we put the following information in:

[mysqld]
query_cache_size=0
binlog_format=ROW
default-storage-engine=innodb
innodb_autoinc_lock_mode=2
query_cache_type=0
bind-address=0.0.0.0

#Galera Provider Configuration
wsrep_on=ON
wsrep_provider=/usr/lib/galera/libgalera_smm.so
#wsrep_provider_options=”gcache.size=32G”

#Galera Cluster Configuration
wsrep_cluster_name=”test_cluster”
wsrep_cluster_address=”gcomm://first_ip,second_ip,third_ip”

#Galera Synchronization Congifuration
wsrep_sst_method=rsync
#wsrep_sst_auth=user:pass

#Galera Node Configuration
wsrep_node_address=”this_node_ip”
wsrep_node_name=”this_node_name”

Now we have to modify some parameters to adapt them to our tutorial. First the line:

           wsrep_cluster_address=”gcomm://first_ip,second_ip,third_ip”

We must add the ip addresses of our nodes, so that’s how it looks:

           wsrep_cluster_address=”gcomm://192.168.250.6,192.168.250.7″

And in the segment: #Galera Node Configuration, we add our parameters

          wsrep_node_address=”192.168.250.6″
           wsrep_node_name=”osradar1″

I remind you that this same file must be created in each of the nodes, modifying the ip address and computer name parameters.

Once this process is done, we must run the mysql_secure_installation script to define root password and other things:

               mysql_secure_installation

We define the root password and answer the questions: Y,N,Y,Y.

For the cluster to work we must add rules in the firewall allowing access through certain ports.

            ufw enable
            ufw allow 3306/tcp
            ufw allow 4444/tcp
            ufw allow 4567/tcp
            ufw allow 4568/tcp
            ufw allow 4567/udp

Configuring Node 2

Previously we must run the mysql_secure_installation script to configure mariadb on this node:

               mysql_secure_installation

We respond in the same way as in the first node.

As mentioned above, we must create the same configuration file but modifying the IP and hostname criteria.

                nano /etc/mysql/conf.d/cluster.cnf

And we also opened the firewall ports:

            ufw enable
            ufw allow 3306/tcp
            ufw allow 4444/tcp
            ufw allow 4567/tcp
            ufw allow 4568/tcp
            ufw allow 4567/udp

As ubuntu is a Debian derivative, we have to copy a configuration file to all nodes. It is important to note that only the file of the first node is useful and should not be modified in the rest of the nodes. That’s why the other nodes must have their own file but must be changed so that it is the same as the first one.

The file is located in /etc/mysql/debian.cfg

Initializing the cluster

Before initializing the cluster we must stop the Mariadb service on all nodes:

             sudo systemctl stop mysql

Now we must initialize the cluster in the first node, to do this:

                galera_new_cluster

With this, you should now start the cluster and the added node 1. To check, we proceed to write:

               mysql -u root -p -e “SHOW STATUS LIKE ‘wsrep_cluster_size'”

When entering the password, we should see something like this:

Now we must go to the second node, and initialize the mariadb service.

              systemctl start mysql

And we return to the first node to verify that the second node has joined the cluster:

mysql -u root -p -e “SHOW STATUS LIKE ‘wsrep_cluster_size'”

Testing the efficacy of the cluster

To prove that the cluster is working in practice is by demonstrating database replication. In the first node, we access mariadb console and create a database:

                mysql -u root -p

next:

               CREATE DATABASE cluster;

and

              SHOW DATABASES;

And in the second node, we show the databases with Show Databases:

This is a tool with great potential, it allows us many possibilities in the segment of database management.

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