Comment 10 for bug 1460577

I've reported this bug and I can give an additional scenario to consider.

If instance is a 'half-pet' (e.g. have some important data), it's natural for operator (tenant) to perform careful shutdown of the instance to avoid any kind of disruption (f.e. by verifying that shutdown was performed fine and all data was saved and is good).

That that person make 'resize', and want to check if instance can start normally before loosing the chance of revert. Currently Openstack prevents this.

Tenant's operator has two options: either trust ACPI shutdown procedures (which are not always as flawless as we want, including angry systemd either waiting forever for some service to stop or killing it on timeout), or migrate instance blindly without chance to start instance.

Start can went wrong on many reasons: minor differences in CPU model, external network issues on provider networks (including obscure things like differences on MTU on uplink devices). So, revert feature is very much welcomed.

Basically, there are two options now:

1. Blindly trust shutdown code and have chance to revert (to the blindly trusted shutdowned state).
2. Or loose 'revert' if shutdown was controlled.