Setup MariaDB Galera Cluster on CentOS 7

Learn how to setup MariaDB Galera Cluster on CentOS 7 with our step-by-step guide. Achieve high availability, data consistency, and improved performance for your database environment. #centlinux #linux #mysql

What is MariaDB Galera Cluster?

MariaDB Galera Cluster is a synchronous multi-master cluster for MariaDB. It is a fork of Galera Cluster, the world’s most advanced, free and open source cluster engine. Currently, it only supports InnoDB storage engines.

MariaDB Galera Cluster is a true Multi-Master and Active-Active cluster. Due to it’s synchronous behaviour, there will be no data lost in case of a node crash because all nodes always hold the same state.

MariaDB Galera Cluster also provides Automatic node provisioning. It means we do not have to manually backup the database and restore it on new node before adding it to Galera cluster. This features gives the additional benefit of Cloud support due to simple scale-in and scale-out operations.

MariaDB Galera Cluster is a high-availability solution for MariaDB that provides synchronous multi-master replication. It’s designed to improve the reliability, scalability, and performance of database environments. Here’s a detailed overview:

Key Features of MariaDB Galera Cluster

Synchronous Replication:

• All transactions are replicated across all nodes in real-time. This ensures that data is always consistent across the cluster.

Multi-Master Architecture:

• Any node in the cluster can handle read and write operations. This enables load balancing and fault tolerance as there’s no single point of failure.

Automatic Node Provisioning:

• New nodes can be added to the cluster easily. Galera Cluster automatically synchronizes data between the new node and the existing nodes.

High Availability:

• If one node fails, the remaining nodes continue to operate normally. This ensures continuous database service with minimal downtime.

Scalability:

• You can scale out by adding more nodes to the cluster to handle increased load. All nodes work together to manage the database operations.

Automatic Failover and Recovery:

• The cluster automatically handles failover, redirecting traffic from failed nodes to healthy nodes, and recovers nodes when they come back online.

Data Consistency:

• Ensures that all nodes have the same data at any point in time, thanks to the synchronous replication mechanism.

Granular Control:

• Supports features like flow control, which helps manage the speed of replication to prevent overloading slower nodes.

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How It Works

Transaction Handling:

• When a transaction is committed on any node, it is replicated to all other nodes in the cluster. All nodes must agree on the transaction before it is committed, ensuring consistency.

Certification-Based Replication:

• Galera uses a certification-based replication model where transactions are certified for consistency before they are applied to other nodes.

Group Communication System:

• Galera uses a group communication system to manage the cluster membership, replication, and failover processes.

Use Cases

• High Availability Applications: Applications that require continuous database access with minimal downtime.
• Load Balancing: Distributing database queries across multiple nodes to improve performance.
• Data Redundancy: Ensuring data is replicated across multiple nodes to prevent data loss.

Summary Table

This overview should give you a good understanding of what MariaDB Galera Cluster is and why it might be a valuable solution for your database needs.

Read Also: Install MariaDB Galera Cluster on Rocky Linux 9

Linux Server Specification

In this article, we will create a two-node MariaDB Galera Cluster of MariaDB 10.3 Database on CentOS 7. However, the same steps can be used to setup MariaDB Galera Cluster of larger size.

For this article, we are using two CentOS 7 virtual machines as the Galera Cluster nodes.

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Install MariaDB Database Server on CentOS 7

Connect to mariadb-01.example.com using ssh as root user.

To setup MariaDB Galera Cluster, you need to install MariaDB and MaxScale yum repositories.

curl -sS https://downloads.mariadb.com/MariaDB/mariadb_repo_setup | bash

Output:

[info] Repository file successfully written to /etc/yum.repos.d/mariadb.repo.
[info] Adding trusted package signing keys...
[info] Succeessfully added trusted package signing keys.

Build yum cache for all repositories.

yum makecache fast

Output:

Loaded plugins: fastestmirror
Determining fastest mirrors
 * base: repo.inara.pk
 * extras: repo.inara.pk
 * updates: repo.inara.pk
base                                       | 3.6 kB     00:00
extras                                     | 3.4 kB     00:00
mariadb-main                               | 2.9 kB     00:00
mariadb-maxscale                           | 2.4 kB     00:00
mariadb-tools                              | 2.9 kB     00:00
updates                                    | 3.4 kB     00:00
(1/5): mariadb-maxscale/7/x86_64/primary_db     | 6.7 kB   00:02
(2/5): mariadb-tools/7/x86_64/primary_db        |  11 kB   00:02
(3/5): mariadb-main/7/x86_64/primary_db         |  50 kB   00:03
(4/5): extras/7/x86_64/primary_db               | 156 kB   00:04
(5/5): updates/7/x86_64/primary_db              | 1.4 MB   00:09
Metadata Cache Created

Install MariaDB Server and Galera using yum command.

yum install -y mariadb-server galera

Repeat above steps on all other nodes.

Setup MariaDB Galera Cluster on CentOS 7

Allow MariaDB and Galera service ports in Linux firewall.

firewall-cmd --permanent --add-service=mysql
firewall-cmd --permanent --add-port={4567,4568,4444}/tcp
firewall-cmd --reload

Set SELinux to permissive mode for now, and we will enable the enforcing mode later, after creating an SELinux policy for MariaDB Galera cluster.

setenforce 0

Now edit MariaDB configuration file.

vi /etc/my.cnf.d/server.cnf

and configure galera section as follows:

[galera]
# Mandatory settings
wsrep_on=ON
wsrep_provider=/usr/lib64/galera/libgalera_smm.so
wsrep_cluster_address=gcomm://192.168.116.81,192.168.116.82
binlog_format=row
default_storage_engine=InnoDB
innodb_autoinc_lock_mode=2

Perform above steps on each node.

Start Galera cluster on mariadb-01.example.com.

galera_new_cluster

Start MariaDB service on all other nodes.

systemctl start mariadb.service

If the service started successfully then, it shows that we have successfully configured our Galera cluster.

Configure MariaDB database instance on each node.

mysql_secure_installation

Output:

NOTE: RUNNING ALL PARTS OF THIS SCRIPT IS RECOMMENDED FOR ALL MariaDB
      SERVERS IN PRODUCTION USE!  PLEASE READ EACH STEP CAREFULLY!

In order to log into MariaDB to secure it, we'll need the current
password for the root user.  If you've just installed MariaDB, and
you haven't set the root password yet, the password will be blank,
so you should just press enter here.

Enter current password for root (enter for none):
OK, successfully used password, moving on...

Setting the root password ensures that nobody can log into the MariaDB
root user without the proper authorisation.

Set root password? [Y/n] Y
New password:
Re-enter new password:
Password updated successfully!
Reloading privilege tables..
 ... Success!


By default, a MariaDB installation has an anonymous user, allowing anyone
to log into MariaDB without having to have a user account created for
them.  This is intended only for testing, and to make the installation
go a bit smoother.  You should remove them before moving into a
production environment.

Remove anonymous users? [Y/n] Y
 ... Success!

Normally, root should only be allowed to connect from 'localhost'.  This
ensures that someone cannot guess at the root password from the network.

Disallow root login remotely? [Y/n] Y
 ... Success!

By default, MariaDB comes with a database named 'test' that anyone can
access.  This is also intended only for testing, and should be removed
before moving into a production environment.

Remove test database and access to it? [Y/n] Y
 - Dropping test database...
 ... Success!
 - Removing privileges on test database...
 ... Success!

Reloading the privilege tables will ensure that all changes made so far
will take effect immediately.

Reload privilege tables now? [Y/n] Y
 ... Success!

Cleaning up...

All done!  If you've completed all of the above steps, your MariaDB
installation should now be secure.

Thanks for using MariaDB!

Connect with MariaDB instance on any node.

mysql -u root -p

Check status of wsrep_cluster_size variable.

show global status like 'wsrep_cluster_size';

Output:

+--------------------+-------+
| Variable_name      | Value |
+--------------------+-------+
| wsrep_cluster_size | 2     |
+--------------------+-------+
1 row in set (0.083 sec)

wsrep_cluster_size confirms that all of our nodes are now connected in Galera cluster.

Create SELinux Policy for MariaDB Galera cluster

Since, we have configured SELinux in permissive mode. Therefore, all the violations by MariaDB and Galera has been recorded in /var/log/audit/audit.log. We can use it to create a concrete SELinux policy.

Use fgrep and audit2allow commands to extract policy violations log into a text file.

fgrep "mysqld" /var/log/audit/audit.log | audit2allow -m MySQL_galera -o MySQL_galera.te

Compile these logs to a SELinux policy module.

checkmodule -M -m MySQL_galera.te -o MySQL_galera.mod

Output:

checkmodule:  loading policy configuration from galera.te
checkmodule:  policy configuration loaded
checkmodule:  writing binary representation (version 19) to MySQL_galera.mod

Create a package of compiled policy module.

semodule_package -m MySQL_galera.mod -o MySQL_galera.pp

Import this policy into SELinux.

semodule -i MySQL_galera.pp

Set SELinux to run in enforcing mode.

setenforce 1

Test SELinux is working fine by restart MariaDB service on each node.

Finally, enable the MariaDB service on all nodes.

systemctl enable mariadb.service

We have successfully configured a MariaDB Galera Cluster on CentOS 7. Although we have configured a two node cluster, but the same steps are good enough for configuring a MariaDB Galera cluster of larger size.

After configuring a MariaDB Galera Cluster, you should be looking next for a database proxy to perform load balancing and routing for our cluster. Therefore, it is highly recommended that you should read our next post to Setup MariaDB MaxScale on CentOS 7.

Frequently Asked Questions (FAQs)

What is MariaDB Galera Cluster?
MariaDB Galera Cluster is a synchronous multi-master database cluster that provides high availability, scalability, and data consistency across all nodes.

Why use Galera Cluster instead of standalone MariaDB?
Galera Cluster ensures automatic failover, load balancing, and no single point of failure, making it ideal for high-availability applications.

What are the minimum system requirements?
You need at least two CentOS 7 servers with sufficient RAM, CPU, and network connectivity. A third node is recommended for quorum and stability.

Do all nodes need identical configurations?
Yes, for consistency, all nodes should have the same MariaDB version, configuration files, and database schemas to avoid conflicts.

How does data synchronization work in Galera Cluster?
Changes made on any node are replicated synchronously to all other nodes, ensuring real-time data consistency across the cluster.

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Final Thoughts

Setting up a MariaDB Galera Cluster on CentOS 7 provides a robust, synchronous multi-master replication solution for high availability and data consistency across database nodes.

By installing the necessary packages, configuring each node correctly, and initializing the cluster, you’ve built a resilient database infrastructure capable of handling failovers and maintaining uptime. Ongoing monitoring, proper firewall settings, and regular maintenance are essential to ensure the cluster remains stable, secure, and performant in production environments.

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