$dc.$domain must not be publicly resolvable.

[csawyerYumaed]

According to IRC, my headnode install failures was from using a domain that's publicly resolvable. This is apparently a sin. so I suggest a line like this: https://github.com/joyent/triton/pull/253

be merged into the CoaL docs, so future uninformed people like me can hopefully not have 3 failures before success.