Cloned from launchpad blueprint https://blueprints.launchpad.net/nova/+spec/user-defined-resume.

Description:

The configuration option resume_guests_state_on_host_boot defines
a global policy on whether or not to restart instances when a host
reboots.  Because a host may be down for a significant period of
time many cloud applications monitor their own instances and launch
replacements restarting all instances is rarely the required behavior

This blueprint provides the user with a mechanism to specify at create
time which of their instances should be restarted on a host reboot.

Initially  three values will be accepted:
    RESUME_DEFAULT -   Follow the resume policy configured in the system
    RESUME_NEVER      -  Don't resume the instance
    RESUME_ALWAYS    -  Always resume the instance

Ideally we would allow the user to specify max_downtime policy where instances
are only resumed is the host has been stopped for less that the user specified
duration (i.e  "Only resume if the host is  down for less than 5 minutes") - but not
all ServiceGroup Drivers can support this model   

Specification URL (additional information):

None