How to setup HAProxy as Load Balancer for MariaDB on CentOS 7

In this tutorial, I will guide you trough the installation of a MariaDB Galera cluster on CentOS 7 which has an HAProxy load balancer in front. The total setup consists of 4 servers. I will use 3 CentOS 7 servers for the database nodes, 2 nodes will be active and 1 acts as the backup node. The fourth server will be used for the HAProxy load balancer. For the balance algorithm, we use leastconn (but you can use other algorithms).