Add ability to create live snapshot for VMs

We discussed this pretty extensively on the mailing list and in a design summit session. The consensus is that this is not a feature we would like to have in nova. --russellb

XCP/XenServer has snapshots that include the memory state, but there is no easy way to export them, but it should be possible. Also, we will need checks similar to live-migrate to ensure the CPU is sufficiently similar for the VM to resume - johnthetubaguy

Overall direction looks good. There are quota concerns and this is more of a virt feature than a cloud feature, but it could still be a useful one to have. --Vish

So far, I think this will be easy for us to do in the VMwareAPI driver. Our problem right now is just whether we have bandwidth to get it done quickly. --hartsocks (VMware sub-team guy)

CLI:

nova state-save <instance-uuid> <state-name>

 Save instance <instance-uuid> state to save <state-name>

nova state-load <instance-uuid> <state-uuid>

 Reset instance <instance-uuid> state to save <state-uuid>

nova state-list <instance-uuid>

 View saved VM states for instance <instance-uuid>

nova state-delete <instance-uuid> <state-uuid>{1,}

 Delete listed saved VM states for instance <instance-uuid>

VM Saved State Nova API Extension:

GET instances/<instance-uuid>/states
Get saved VM states for instance
Issue call to DB

Response:
{
    “values”: [
                      {
                         “uuid”: “<state-uuid>”,
                         “name”: “<state name>”,
                         “date”: <creation date>,
                      },
                      ...
                  ],
}

GET instances/<instance-uuid>/states/<state-uuid>
Get saved VM state for instance
Issue call to DB

Response:

{
   “uuid”: “<state-uuid>”,
   “name”: “<state name>”,
   “date”: <creation date>,
}

POST instances/<instance-uuid>/states
Save VM state
Get instance info from DB
Send “save” through AMPQ on compute node channel that holds instance.

Data:
{
     “name”: “<save name>”,
}

DELETE instances/<instance-uuid>/states/<state-uuid>
Delete saved VM state
Get instance info from DB
Send “delete_state” through AMPQ on compute node channel that holds instance.

POST instances/<instance-uuid>/states/apply
Apply saved VM state
Get instance info from DB
Send “restore” through AMPQ on compute node channel that holds instance.

Data:
{
     “uuid”: “<state-uuid>”.
}

Nova Compute Changes:

1. Add
state_save(instance_uuid, state_name),
state_restore(instance_uuid, state_uuid),
state_delete(instance_uuid, state_name)
methods to nova.virt.driver

2. Implement state_save, state_restore, state_delete in nova.virt.libvirt.driver using libvirt API. Throw Exception in case when backend format is not Qcow2 or leave decision to libvirt.

3. Add instance_states table to DB

4. Associate it with InstanceState model:
      uuid: state uuid, <primary key>
      name: state name
      date: state date (automatically filled)

5. Add migration script for instance_states

6. Implement instance_state_create, instance_state_get, instance_state_destroy in DB API