designate does not handle compute.instance.update events

[Dmitrii Shcherbakov]

It would be instrumental for designate to handle instance update events coming from nova over AMQP as DNS names may change over the lifetime of an instance.

Moreover, format{v4,v6} may depend on a display_name of a given node which may change.

Currently only compute.instance.create.end and compute.instance.delete.start are processed in designate:

https://github.com/openstack/designate/blob/stable/pike/designate/notification_handler/nova.py#L58-L62

nova code-path:

https://github.com/openstack/nova/blob/stable/pike/nova/objects/instance.py#L665-L812
    def save(self, expected_vm_state=None,
             expected_task_state=None, admin_state_reset=False):
        """Save updates to this instance
...
         notifications.send_update(context, old_ref, new_ref)
...

https://github.com/openstack/nova/blob/stable/pike/nova/notifications/base.py#L220-L251
def send_update(context, old_instance, new_instance, service="compute",
...
        send_update_with_states(context, new_instance, old_vm_state,
...
        try:
            old_display_name = None
            if new_instance["display_name"] != old_instance["display_name"]:
                old_display_name = old_instance["display_name"]
            send_instance_update_notification(context, new_instance,
...

https://github.com/openstack/nova/blob/stable/pike/nova/notifications/base.py#L220-L251
def send_instance_update_notification(context, instance, old_vm_state=None,
            old_task_state=None, new_vm_state=None, new_task_state=None,
            service="compute", host=None, old_display_name=None):
    """Send 'compute.instance.update' notification to inform observers
    about instance state changes.
    """
    payload = info_from_instance(context, instance, None, None) # <--- default payload
...
    if old_display_name:
        payload["old_display_name"] = old_display_name

    rpc.get_notifier(service, host).info(context,
                                         'compute.instance.update', payload) # <--- actual notification
...

[Graham Hayes (grahamhayes)]

This seems like a nice to have - no objections to the code being written, but it wil not be a priority