Boot instance specific storage backend

This blueprint proposes adding support for specifying volume_type when booting instances.

Problem description

Currently, when creating a new boot-from-volume instance, the user can only control the type of the volume by pre-creating a bootable image-backed volume with the desired type in cinder and providing it to nova during the boot process. When the user wants to boot the instance on the specified backend, this is not friendly to the user when there are multiple storage backends in the environment.

Use Cases

As a user, I would like to specify volume type to my instances when I boot them, especially when I am doing bulk boot. The “bulk boot” means creating multiple servers in separate requests but at the same time.

However, if the user wants to boot instance on a different storage backends, they only need to specify a different backend to send the create request again.

Proposed change

Add a new microversion to the servers create API to support specifying volume type when booting instances.

This would only apply to BDMs with source_type of blank, image and snapshot. The volume_type will be passed from nova-api through to nova-compute (via the BlockDeviceMapping object) where the volume gets created and then attached to the new server.

The nova-api service will validate that the requested volume_type actually exists in cinder so we can fail fast if it does not or the user does not have access to it.


You can also combine cinder and nova to do this.

  • Create the volume with the non-default type in cinder and then provide the volume to nova when creating the server.

Data model impact

We’ll have to store the volume_type on the BlockDeviceMapping object (and block_device_mapping table in the DB).

REST API impact

  • URL:
    • /v2.1/servers:

  • Request method:
    • POST

The volume_type data will be able to add to request payload

    "server" : {
        "name" : "device-tagging-server",
        "flavorRef" : "",
        "networks" : [{
            "uuid" : "ff608d40-75e9-48cb-b745-77bb55b5eaf2",
            "tag": "nic1"
        "block_device_mapping_v2": [{
            "uuid": "70a599e0-31e7-49b7-b260-868f441e862b",
            "source_type": "image",
            "destination_type": "volume",
            "boot_index": 0,
            "volume_size": "1",
            "tag": "disk1",
            "volume_type": "lvm_volume_type"

Security impact


Notifications impact

Add volume_type field to BlockDevicePayload object.

Other end user impact

The python-novaclient and python-openstackclient will be updated.

When we snapshot a volume-backed server, the block_device_mapping_v2 image metadata will include the volume_type from the BDM record so if the user then creates another server from that snapshot, the volume that nova creates from that snapshot will use the same volume_type. If a user wishes to change that volume type in the image metadata, they can via the image API. For more information on image-defined BDMs, see [1] and [2].

Performance Impact


Other deployer impact


Developer impact


Upgrade impact

To support rolling upgrades, the API will have to determine if the minimum nova-compute service version across the deployment (all cells) is high enough to support user-specified volume types. If volume_type is specified but the deployment is not new enough to handle it, a 409 error will be returned to the user.



Primary assignee:

Brin Zhang

Work Items

  • Add volume_type support in compute API

  • Add related tests




  • Add Tempest integration tests for scenarios like:

    • Boot from volume with a non-default volume type.

    • Snapshot a volume-backed instance and assert the non-default volume type is stored in the image snapshot metadata.

  • Add related unit test for negative scenarios like:

    • Attempting to boot from volume with a specific volume type before the new microversion.

    • Attempting to boot from volume with a volume type that does not exist and/or the user does not have access to.

    • Attempting to boot from volume with a volume type with old computes that do not yet support volume type.

  • Add related functional tests for positive scenarios

    • The functional API samples tests will cover the positive scenario for boot from volume with a specific volume type and all computes in all cells are running the latest code.

Documentation Impact

Add docs that mention the volume type can be specified when boot instances after the microversion.


For a discussion of this feature, please refer to:


Revisions :header-rows: 1

Release Name