Introduction

SQL Galera Cluster is a popular high-availability solution for MySQL and MariaDB databases. It provides synchronous multi-master replication, ensuring consistent data across multiple database nodes within a single datacenter. However, to achieve cross-datacenter replication, additional steps need to be taken. In this blog post, we will discuss how to implement cross-datacenter replication in SQL Galera Cluster.

Prerequisites

To follow along with this tutorial, you must have the following:

1. SQL Galera Cluster installed and configured in each datacenter.
2. A reliable network connection between the datacenters.
3. Familiarity with SQL Galera Cluster concepts and configuration.

Steps to Implement Cross-Datacenter Replication

Step 1: Setup Primary and Backup Clusters

In each datacenter, you need to set up a SQL Galera Cluster. One cluster will act as the primary cluster, while the other will serve as a backup cluster. Ensure both clusters are properly configured and functioning as expected within their respective datacenters.

Step 2: Enable Binary Logging and GTID

To enable cross-datacenter replication, you need to enable binary logging and Global Transaction Identifier (GTID) on each cluster. This ensures data consistency and enables easy identification of replicated transactions.

To enable binary logging, add the following line to the my.cnf configuration file of each cluster:

[mysqld]
log-bin=binlog

To enable GTID, add the following line to the same my.cnf file:

[mysqld]
gtid_mode=ON

Step 3: Configure Replication between Clusters

To configure cross-datacenter replication, you need to establish a connection between the primary and backup clusters. This is achieved by setting up a master-slave relationship.

On the primary cluster, open the MySQL shell and execute the following SQL command:

GRANT REPLICATION SLAVE ON *.* TO 'replication_user'@'<backup_cluster_ip>' IDENTIFIED BY 'password';
FLUSH PRIVILEGES;

Replace <backup_cluster_ip> with the IP address of the backup cluster and provide a secure password for the replication user.

On the backup cluster, open the MySQL shell and execute the following SQL command:

CHANGE MASTER TO MASTER_HOST='<primary_cluster_ip>', MASTER_USER='replication_user', MASTER_PASSWORD='password';
START SLAVE;

Replace <primary_cluster_ip> with the IP address of the primary cluster and use the same replication user and password specified in the previous step.

Repeat these steps in reverse for setting up replication from the backup cluster to the primary cluster.

Step 4: Monitor Replication Status

To ensure the replication is working correctly, you need to monitor the replication status. Use the following SQL command on each cluster to view the replication status:

SHOW SLAVE STATUS\G

Check the Slave_IO_Running and Slave_SQL_Running fields to ensure both are set to Yes, indicating that replication is active and running smoothly.

Conclusion

By following these steps, you can successfully implement cross-datacenter replication in SQL Galera Cluster. This ensures data consistency and availability across multiple datacenters, providing a robust and reliable database solution. With cross-datacenter replication, you can achieve geographic redundancy and disaster recovery capabilities for your MySQL or MariaDB databases.

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