"The cluster I'm going to create will be named
cluster1.example.com, and it will have the IP address
192.168.0.102. The cluster IP 192.168.0.102 will always be bound to
the cluster master, so even if you don't know which node is the
master, you can use the cluster IP (or the hostname
cluster1.example.com) to connect to the master using SSH.
"The Xen virtual machine (called an instance in Ganeti speak)
will be named inst1.example.com with the IP address 192.168.0.105.
inst1.example.com will be mirrored between the two physical nodes
using DRBD - you can see this as a kind of network RAID1.
"As you see, node1.example.com will be the cluster master, i.e.
the machine from which you can control and manage the cluster, and
node2.example.com will be the primary node of inst1.example.com,
i.e. inst1.example.com will run on node2.example.com (with all
changes on inst1.example.com mirrored back to node1.example.com
with DRBD) until you fail it over to node1.example.com (if you want
to take down node2.example.com for maintenance, for example). This
is an active-passive configuration."