Remote into Mac Mini after a reboot

How can a Mac running El Capitan always be ready for a VNC connection even after a reboot? I can vnc into the Mac with no problem but when I reboot the Mac remotely I can't vnc back in. Someone has to hook up a keyboard to the Mac and physically log in and log back out. Once the machine has been logged in locally I can once again log in remotely via Mac. I'm using the Mac's built-in VNC as well as an installed RealVNC server. Neither will respond after a reboot. I edited the RealVNC launch daemon to run at load but that didn't work. UPDATE The mac has filevault turned on. 'sudo fdesetup authrestart' will work with a manual reboot. It will not work however with a forced system reboot or a power outage. Someone would still need to manually login with a keyboard in those cases. The options at this point seem to be to disable Filevault or accept the fact that a person will need to login occasionally.