Overview
Services or scripts may be set to run upon server start within the control panel or via crontab(5) from the terminal. Either solution requires task scheduling support, which is found on Developer+ packages.
Within the control panel
Visit Dev > Task Scheduler to add a new routinely scheduled task. Command syntax follows the same as a normal task, but for the time specification, select @reboot. The job will start on server start. If there are issues with starting the application or the application fails to remain running, then it will remain down.
From the terminal
Use crontab -e to edit your crontab. Instead of specifying a time (min/hour/day/day of week/day of month), specify @reboot, e.g.
@reboot touch /tmp/restart