"In a group of MMM-managed machines, each node has a node IP,
which is the normal server IP address. In addition, each node has a
"read" IP and a "write" IP. Read and write IPs are moved around
depending on the status of each node as detected and decided by
mmmd_mon, which migrates these IP address around to ensure that the
write IP address is always on an active and working master, and
that all read IPs are connected to another master that is in sync
(which does not have out-of-date data).
"mmmd_mon should not run on the same server as any of the
databases to ensure good availability. Thus, the best practice
would be to keep a minimum number of three nodes.
"In the examples of this article, we will configure two MySQL
servers, node 5 and node 6 (10.0.0.5 and 6) with a virtual writable
IP of 10.0.0.10 and two read-only IPs of 10.0.0.11 and 10.0.0.12,
using a monitoring node node 4 (10.0.0.4). We will use RedHat /
CentOS provided software where possible."