Galera Cluster is a robust, synchronous, multi-master cluster offering true active-active capabilities with no replication lag or lost transactions. In contrast, traditional MySQL active-active setups rely on asynchronous replication with potential lag and conflicts, making Galera Cluster a superior choice for applications needing strong consistency and high availability.

Ultimate Beginner’s Guide to Setting Up MariaDB Galera Cluster for High Availability

MariaDB Galera Cluster offers a powerful multi-primary database clustering solution that ensures high availability, fault tolerance, and real-time synchronous replication across multiple database nodes. It’s perfect for mission-critical applications that need zero lag and no data loss during replication.

This guide walks through the entire process of setting up a three-node MariaDB Galera Cluster from scratch, designed for beginners and Linux users who want a reliable, scalable database cluster.

output

What Is MariaDB Galera Cluster?

MariaDB Galera Cluster is a multi-master (active-active) database cluster allowing all nodes to handle reads and writes simultaneously. Every transaction is replicated synchronously to all nodes, ensuring all data stays perfectly in sync without delay or risk of lost transactions. It’s available exclusively on Linux and works best with at least three nodes for resilience.

Step 1: Prepare Your Environment

Before setting up the cluster, make sure you have:

Three Linux nodes (bare-metal or VMs) with Debian, Ubuntu, CentOS, or Fedora OS.
Synchronized system clocks using NTP for accurate timing.
Root or sudo access on all nodes.
Proper network connectivity with low latency between nodes.
Installed rsync on each node (used for synchronizing database state):

sudo apt install rsync       # Debian/Ubuntu
sudo yum install rsync       # CentOS/RHEL

Step 2: Install MariaDB and Galera on All Nodes

Add MariaDB Official Repository (Debian/Ubuntu example):

sudo apt update
sudo apt install dirmngr software-properties-common apt-transport-https ca-certificates curl -y
curl -LsS https://r.mariadb.com/downloads/mariadb_repo_setup | sudo bash
sudo apt update

Install MariaDB Server, Client, and Galera Provider:

sudo apt install mariadb-server mariadb-client galera-4 -y

(Note: Use galera-4 for MariaDB 10.4+ versions.)

Step 3: Secure MariaDB Installation

Run the security script on each node to set root passwords and harden security:

sudo mariadb-secure-installation

Set a strong root password.
Remove anonymous users.
Disallow remote root login.
Remove the test database.
Reload privilege tables.

Step 4: Configure Firewall Rules on Each Node

Enable ports essential for Galera Cluster communication:

sudo ufw allow 3306/tcp    # MariaDB client port
sudo ufw allow 4567/tcp    # Galera replication (reliable)
sudo ufw allow 4567/udp    # Galera replication (for multicast)
sudo ufw allow 4568/tcp    # Incremental State Transfer (IST)
sudo ufw allow 4444/tcp    # State Snapshot Transfer (SST)
sudo ufw reload
sudo ufw enable

Adapt commands if you use firewalld or another firewall system.

Step 5: Create Galera Configuration File on Each Node

Create /etc/mysql/conf.d/galera.cnf with this content, changing node names and IPs accordingly:

[mysqld]
binlog_format=ROW
default_storage_engine=InnoDB
innodb_autoinc_lock_mode=2
bind-address=0.0.0.0

wsrep_on=ON
wsrep_provider=/usr/lib/galera/libgalera_smm.so  # Adjust path if needed

wsrep_cluster_name="my_galera_cluster"
wsrep_cluster_address="gcomm://node1_ip,node2_ip,node3_ip"

wsrep_node_name="nodeX"           # Unique name, e.g., node1, node2, node3
wsrep_node_address="nodeX_ip"     # Node’s exact IP address

Replace node1_ip, node2_ip, and node3_ip with your actual node IPs.
Ensure each node’s name and IP address are unique.

Step 6: Start Your MariaDB Galera Cluster

Bootstrap the First Node (only once):

sudo systemctl stop mariadb
sudo galera_new_cluster

Or:

sudo systemctl start mariadb --wsrep-new-cluster

Start Other Nodes Normally:

sudo systemctl start mariadb

These nodes will automatically join the cluster based on the configuration.

Step 7: Verify Cluster Status and Replication

Connect to MariaDB on any node:

sudo mariadb -u root -p
SHOW STATUS LIKE 'wsrep_cluster_size';

The number displayed should match your total nodes (e.g., 3).

Test Replication Across Nodes

On node1:

CREATE DATABASE test_db;
USE test_db;
CREATE TABLE messages (
  id INT AUTO_INCREMENT PRIMARY KEY,
  text VARCHAR(255)
);
INSERT INTO messages (text) VALUES ('Hello from node1!');

On node2 or node3, check the data:

SHOW DATABASES;  -- test_db should appear
USE test_db;
SELECT * FROM messages;  -- 'Hello from node1!' should appear

Insert data on node2:

INSERT INTO messages (text) VALUES ('Hello from node2!');

Verify on node1:

SELECT * FROM messages;  -- 'Hello from node2!' should appear

Final Tips

Use private IPs for cluster traffic to enhance security.
Regularly monitor cluster status and logs to detect any network or state issues.
Back up your database regularly even with high availability.
For production, tweak advanced settings like SST method, authentication, and encryption as per your security needs.

With this guide, anyone can set up a robust MariaDB Galera Cluster ensuring continuous availability and strong data consistency across multiple nodes. Happy clustering!

Reference MariaDB Galera Cluster Guide - mariadb.com

https://medium.com/mr-dops/mariadb-with-galera-cluster-8ded2e83721b

Setting Up MariaDB Galera Cluster (Active Active) for High Availability