It is safe to shut down a master server and restart it later.
When a slave loses its connection to the master, the slave tries
to reconnect immediately and retries periodically if that fails.
The default is to retry every 60 seconds. This may be changed
CHANGE MASTER TO
--master-connect-retry option. A
slave also is able to deal with network connectivity outages.
However, the slave notices the network outage only after
receiving no data from the master for
slave_net_timeout seconds. If
your outages are short, you may want to decrease
Section 5.1.4, “Server System Variables”.