add a basic glossary to the tutorial

# Tutorial

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In Ganeti, a physical machine is called a *node* and a virtual machine

is an *instance*. A node is elected to be the *master* where all

commands should be ran from. Nodes are interconnected through a

private network that is used to communicate commands and synchronise

disks (with [[drbd]]). Instances are normally assigned two nodes: a

*primary* and a *secondary*: the *primary* is where the virtual

machine actually runs and th *secondary* acts as a hot failover.

## Listing instances