pmacontrol / haproxy_galera_check

Shell script to check and report the status of a Galera node to HAproxy

clusterchk: Galera cluster status check script with HAproxy

This repo contains a shell script which checks the status of a MySQL instance part of a Galera cluster and reports an HTTP message to HAproxy if the node is in sync with the rest of the cluster or not.

The script implements the following algorithm:

The main idea came from the following article: https://severalnines.com/resources/tutorials/mysql-load-balancing-haproxy-tutorial

Limitations

At the moment the script is designed to be executed only on Debian/Ubuntu Linux distributions, since it is relying on the sys-maint user defined under /etc/mysql/debian.cnf in order to connect to the MySQL instance.

HAproxy

The main point of using HAproxy is to balance TCP connections between application servers and the Galera cluster, not to mention the possibility of logically separate the database servers from the DMZ network.

(Reference: http://galeracluster.com/documentation-webpages/haproxy.html)

HAproxy is a generic load balancer and proxy server for TCP and HTTP based applications, so it does not concern itself with the status of the servers on the other side: either they are available or it will select other destinations, based on different routing policies ( Round Robin, Least Connected, Source Tracking, etc.).

The problem with Galera is that the MySQL server which HAproxy has selected can be up&running but it could be that the internal status is not Synced with the rest of the cluster.

An example on how to configure HAproxy to run the shell script is available under the haproxy subdirectory.

Running clusterchk using SystemD

As a quick test, the script can be executed also directly on the command line but in production the main idea is to use the SystemD units available under the systemd subdirectory.