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

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