nova/doc/notification_samples/instance-reboot-start.json

{
    "event_type":"instance.reboot.start",
    "payload":{
        "$ref":"common_payloads/InstanceActionPayload.json#",
        "nova_object.data":{
            "task_state":"reboot_pending_hard"
        }
    },
    "priority":"INFO",
    "publisher_id":"nova-compute:compute"
}