I helped architect and build a system to get 4 nines
(99.99) availability for the mysql backend behind a website. It used
mysql replication to set up a multi-master environment, MMM to manage it
and LVS for mysql backend loadbalancing. This architecture not only
provided high availability, but also permitted us to
change the schema, upgrade MySQL versions, or even replace
hardware without any downtime. This presentation explains
how this solution worked.