Ales Nosek - The Software Practitioner

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Jan 31, 2016 - Comments - cloud devops

Bootstrapping a Galera Cluster on RHEL7

The MariaDB Galera packages provided by the RDO project in their OpenStack repositories don’t seem to include a command or script to bootstrap the cluster. Let’s look at an alternative way to bring the cluster up.

RHEL7 comes with the init system systemd. Unfortunately, systemd doesn’t provide a way to pass command-line arguments to the unit files. Hence, doing something like this won’t work:

$ systemctl start mariadb --wsrep_new_cluster
systemctl: unrecognized option '--wsrep_new_cluster'

Instead of passing command-line arguments, systemd allows for creating multiple instances of the same service where each instance can obtain it’s own set of environment variables. The Percona XtraDB Cluster includes the standard and the bootstrap service instance definitions in the RPM package Percona-XtraDB-Cluster-server. To boostrap the Percona cluster, the first node can be started with the following command:

$ systemctl start mysql@bootstrap.service

At the moment, this boostrap service definition is missing in the RDO OpenStack packages. Before a similar mysql@.service script is available in RDO you can start the MariaDB Galera cluster as follows:

  • On the first node, start the MariaDB with the --wsrep-new-cluster to create a new cluster:

    $ /usr/bin/mysqld_safe --wsrep-new-cluster
    Let the command run in the foreground.

  • On the remaining cluster nodes start the mariadb service as usual:

    $ systemctl start mariadb

  • After the cluster has been fully formed, stop the mariadb on the first node by sending it a SIGQUIT (press CTRL + \ on the console).

  • On the first node, start the mariadb service via systemd:

    $ systemctl start mariadb

That’s it. You can check the status of each of the cluster nodes by running the following command:

$ mysql -e "SHOW GLOBAL STATUS LIKE 'wsrep%';"