cinder/api-ref/source/v3/samples/attachment-list-response.json

{
    "attachments": [
        {
            "status": "attaching",
            "instance": "31c79baf-b59e-469c-979f-1df4ecb6eea7",
            "id": "3b8b6631-1cf7-4fd7-9afb-c01e541a073c",
            "volume_id": "462dcc2d-130d-4654-8db1-da0df2da6a0d"
        }
    ]
}