Chapter 20. Identifying virtual devices with tags

20.1. Overview of virtual device tagging

If you launch an instance with multiple network interfaces or block devices, you can use device tagging to communicate the intended role of each device to the instance operating system. Tags are assigned to devices at instance boot time, and are available to the instance operating system through the metadata API and the configuration drive (if enabled).

The tags are set using the following parameters:

  • --block-device tag=device metadata
  • --nic tag=device metadata

20.2. Tagging virtual devices

  • To tag virtual devices, use the tag parameters, --block-device and --nic, when creating instances.

    Here is an example: 

    $ nova boot test-vm --flavor m1.tiny --image cirros \
--nic net-id=55411ca3-83dd-4036-9158-bf4a6b8fb5ce,tag=nfv1 \
--block-device id=b8c9bef7-aa1d-4bf4-a14d-17674b370e13,bus=virtio,tag=database-server NFVappServer

    The resulting tags are added to the existing instance metadata and are available through both the metadata API, and on the configuration drive.

    In this example, the following devices section populates the metadata:

    Sample contents of the meta_data.json file: 

        {
  "devices": [
    {
        "type": "nic",
        "bus": "pci",
        "address": "0030:00:02.0",
        "mac": "aa:00:00:00:01",
        "tags": ["nfv1"]
    },
    {
        "type": "disk",
        "bus": "pci",
        "address": "0030:00:07.0",
        "serial": "disk-vol-227",
        "tags": ["database-server"]
    }
  ]
}

    The device tag metadata is available using GET /openstack/latest/meta_data.json from the metadata API.

    If the configuration drive is enabled, and mounted under /configdrive in the instance operating system, the metadata is also present in /configdrive/openstack/latest/meta_data.json.