Fallback/multiple database support

[jcpunk]

I've got a master/master MariaDB setup and I'd love to be able to set multiple hostnames in wordpress to utilize this high availability cluster.

They share user/pass/dbname it is just that I've got multiple dbhosts.

I've little interest in sharding or load balancing between the systems. I just desire: if wordpress can't connect to one host that it tries another.

Yep:
​http://wordpress.org/plugins/hyperdb/

This won't be added to core - but is the standard for setting up your DB cluster.

The listed compatibility of that plugin is way back at 3.5.2

It is used on every major WordPress website. WordPress.com, The New York Times, etc

I'll harass someone to get it updated, but note it works fine with the latest version of WordPress and we use it on WordPress.org (it also powers WordPress.com).