Since modern buildings often have critical things like lighting, HVAC, and water or even security and access control integrated into one automation system, is there any sort of redundancy in the control devices? If the central controller were to crash, would the mechanical and electrical systems in the building grind to a halt or is there usually a backup? If there is, is it done by having two separate controller units that can operate independently other or through some other way?

It's always dns
!sysadmin