Allow configuration of mysql percona sst through xtrabackup-v2

[Joseph Davis]

Currently, tripleo delivers a cluster.cnf for MySQL clustering which defines the wsrep-sst-method as "rsync". While this is simple and works, it can be slow on really large databases.

https://github.com/openstack/tripleo-image-elements/blob/master/elements/mysql-common/os-apply-config/mnt/state/etc/mysql/conf.d/cluster.cnf

The Percona documentation, such as https://www.percona.com/doc/percona-xtradb-cluster/5.5/wsrep-system-index.html, recommends using xtrabackup-v2.

The downside to xtrabackup-v2 is it also requires a user, specified as wsrep_sst_auth, be created in the MySQL database with the correct privileges. This is pretty simple:
GRANT RELOAD, LOCK TABLES, REPLICATION CLIENT ON *.* TO 'sst'@'localhost' IDENTIFIED BY 'secret';

We should provide a way to select the xtrabackup-v2 method of SST replication per-cluster, and have the MySQL element create the user with the right privileges and a fresh, random password.

This password is not to be used by a customer at any time, so it doesn't need to be exposed/configurable through a UI. Also be warned, it appears the password is logged in the MySQL logs, so the password should not be reused from any other, more secure accounts in the cloud.

(thanks to Kyle Smith who reported this issue to me)

[Ben Nemec (bnemec)]

I'm afraid tripleo-image-elements is effectively an abandoned project at this point. All of the people who were actively maintaining the elements have left the project, and the current focus is on a puppet-based deployment method. While I suppose we would take a patch for this, I think it's unlikely to be fixed.