Moodle Clusters
From MoodleDocs
A Moodle cluster, in this sense, is a collection of computers that may or may not mirror a Moodle, but will load share. A lot of people could benefit if they understood how this could be done.
You might want to start here. Linux HA is a project dedicated to developing Linux Clusters.
This initially appears to be the same thing, but then reading it, The Linux Virtual Server project is very different.