Using DNS and defaults for minion connection

In the absence of a "master" param in /etc/salt/minion, the minion will try to tune into the DNS name "salt" in the local domain. So if you have internal DNS on domain 
"saltstack", for instance, then creating a CNAME for "salt.saltstack" and pointing it at your master will allow minions to tune into your master without an /etc/salt/minion file present. 

Of course, another option would be to deploy an /etc/salt/minion with a "master" param pointing at the master IP/hostname: 

master: mymaster.domain
 

We generally recommend setting up a CNAME like in the first option though, because it allows you the flexibility to either

1. not initially deploy an /etc/salt/minion config file,
   or
2. have the deployed /etc/salt/minion have a "master" param which points to a DNS name that can be easily re-assigned without affecting your initial deploy image.