Support Modifying Volume Image Metadata

Include the URL of your launchpad blueprint:

This blueprint intends to support modifying volume image metadata, provide Cinder API to allow a user to modify an image property or add new properties.

Cinder should provide the similar mechanism for protected properties as what Glance did, and it is the agreed approach according to the discussion in the IRC and mailing list.

Problem description

When creating a bootable volume from an image, the image metadata (properties) is copied into a volume property named volume_image_metadata.

Cinder volume_image_metadata is the metadata on bootable volumes that Nova looks at and uses for scheduling as well as for passing along to the individual compute drivers.

Cinder volume_image_metadata is used by nova for things like scheduling and for setting device driver options. nova treat volume_image_metadata the same way as the properties on images. This information may need to change after the volume has been created from an image, besides, the additional properties may also needed to make it available in the scheduler (detailed in the below sections). So, There should be a way to support change/update image metadata.

Use Cases

Here are some types of metadata properties that if set will affect runtime characteristics of how Nova handles the booted volume. Many of them very well could be a user deciding to basically build a new image using a volume, but they want to twiddle with various handling properties as part of the building process. Or they simply may have a bootable volume that they want to modify some of these properties.

Hypervisor selection: OpenStack Compute supports many hypervisors, although most installations use only one hypervisor. For installations with multiple supported hypervisors, you can schedule different hypervisors using the ImagePropertiesFilter. This filters compute nodes that satisfy any architecture, hypervisor type, or virtual machine mode properties specified on the instance’s image properties (also volume_image_properties).

Virtual CPU Topology: This provides the preferred socket/core/thread counts for the virtual CPU instance exposed to guests. This enables the ability to avoid hitting limitations on vCPU topologies that OS vendors place on their products. See also:

Watchdog Behavior: For the libvirt driver, you can enable and set the behavior of a virtual hardware watchdog device for each flavor. Watchdog devices keep an eye on the guest server, and carry out the configured action, if the server hangs. The watchdog uses the i6300esb device (emulating a PCI Intel 6300ESB). If hw_watchdog_action is not specified, the watchdog is disabled. Watchdog behavior set using a specific image’s properties will override behavior set using flavors.

Shutdown Behavior: Numerous things coming: What landed in Juno: By default, guests will be given 60 seconds to perform a graceful shutdown. After that, the VM is powered off. The os_shutdown_timeout property allows overriding the amount of time (unit: seconds) to allow a guest OS to cleanly shut down before power off. A value of 0 (zero) means the guest will be powered off immediately with no opportunity for guest OS clean-up.

Minimum Flavor Requirements: Minimum required CPU, Minimum RAM. These are used by the Horizon UI to guide flavor selection. Somebody with a bootable volume may install some new software on it and play around with setting the minimum requirements before cloning to an image.

The new Horizon UI is going to be providing more information about images, flavors, volumes to admins and users in the UI leveraging the metadata and looking up rich information about the metadata from the definition catalog to display information to users and admins. This can include metadata about software on the volume.

Proposed change

This ONLY affects the individual volume, it’s has nothing to do with volume types

We are proposing the changes in Cinder to add update capability and provide new Cinder API to allow a user to update an image properties.

Since Glance has RBAC (role based access control) on some specific properties, the RBAC config file is proposed to copied from Glance to Cinder, and sync the protected properties code from Glance into Cinder (Glance are happy to take code cleanups that make this easier; we can consider OSLO or whatever in future but that’s a heavy weight process for another day, copy and paste will do for now).


As to the strategy on protected properties, one proposal is providing new API to query the properties protected or so per-property from Glance to Cinder, but his approach seems will increase the overload of Glance.

Data model impact


REST API impact

Since only image metadata is used by nova for VM scheduling or setting device driver options, we proposed to add new REST APIs into Cinder for the operations on image metadata of volume.

  • update image metadata referenced with volume

Common http response code(s)

  • Modify Success: 200 OK
  • Failure: 400 Bad Request with details.
  • Forbidden: 403 Forbidden e.g. no permission to update the
    specific metadata
  • Not found: 501 Not Implemented e.g. The server doesn’t recognize
    the request method
  • Not found: 405 Not allowed e.g. HEAD is not allowed on the resource
Update volume image metadata
  • Method type PUT

  • API version PUT /v2/{project_id}/volumes/{volume_id}/image_metadata

  • JSON schema definition {

    “image_metadata”: {

    “key”: “v2”



    To unset a image metadata key value, specify only the key name. To set a image metadata key value, specify the key and value pair.

Security impact


Notifications impact


Other end user impact

  • We intend to expose this via Horizon and are working on related blueprints.

  • Glance also need share its properties protection code to Cinder and some code cleanups in Glance’s IMPL.

  • Provide Cinder API to allow a user to update an image property. CLI-python API that triggers the update.

    # Sets or deletes volume image metadata cinder image-metadata  <volume-id> set <property-name = value>

Performance Impact

None anticipated.

Other deployer impact

  • Two config file will be added into Cinder, that is property-protections- policies.conf and property-protections-roles.conf These file will be put in “/etc/cinder” by default and is configurable via cinder.conf or point directly at the Glance files in devstack for example.
  • Deployer will be responsible for keeping the config files in sync with Glance’s
  • The config files will only take effect when they are present on the system. So it is up to the deployer to ensure they are accurate. Otherwise, there will be no impact to Cinder of the OpenStack environment by default.

Developer impact




Primary assignee:
Dave Chen (wei-d-chen)
Other contributors:

Work Items

Changes to Cinder:

  1. Define property protections config files in Cinder (Deployer need to keep the files in sync with Glance’s)
  2. Sync the properties protection code from Glance into Cinder (The common protection code will be shared in Cinder)
  3. Extend existing volume_image_metadatas(VolumeImageMetadataController) controller extension to add update capability.
  4. Reuse update_volume_metadata method in volume API for updating image metadata and differentiate user/image metadata by introducing a new constant “meta_type”
  5. Add update_volume_image_metadata method to volume API.
  6. Check against property protections config files (property-protections-policies.conf or property-protections-roles.conf) if the property has update protection.
  7. Update DB API and driver to allow image metadata updates.

Changes to Cinder python client:

  1. Provide Cinder API to allow a user to update an image property. CLI-python API that triggers the update. # Sets or deletes volume image metadata cinder image-metadata  <volume-id> set <property-name = value>


Same dependencies as Glance.


Unit tests will be added for all possible code with a goal of being able to isolate functionality as much as possible.

Tempest tests will be added wherever possible.

Documentation Impact

Since Glance has role based access control to properties. It could be the case that we want to update a property in Cinder that is protected in Glance. Eg: a license key is added in glance and it’s copied to cinder when the volume is created. It should not be changed by an unauthorized user in Cinder because this can be violating the billing policies for that image. Therefore, Property Protections which is similar with Glance is proposed to be adopted into Cinder.

We propose to define two samples config file in favor of Property Protections, that is property-protections-roles.conf and property-protections-policies.conf.

  • property-protections-policies.conf

This is a template file when using policy rule for property protections.

Example: Limit all property interactions to admin only using policy rule context_is_admin defined in policy.json.

create = context_is_admin
read = context_is_admin
update = context_is_admin
delete = context_is_admin
  • property-protections-roles.conf

This is a template file when property protections is based on user’s role. Example: Allow both admins and users with the billing role to read and modify properties prefixed with x_billing_code_.

create = admin,billing
read = admin, billing
update = admin,billing
delete = admin,billing

Please refer to here, for the details explanation of the format.

In case there is property which is protected strictly in Glance, license key for example, deployer should aware the config files may turn out to be inconsistent between Cinder and Glance, it’s up to deployer’s responsibility to keep the config files in sync with Glance’s

Other docs is also needed for new API extension and usage.


This blueprint is actually a partial task of Graffiti project, many parts of this concept have already been implemented for other pieces of OpenStack, but that Cinder is outstanding (already completed for images, flavors, host aggregates)

Youtube summit recap of Graffiti Juno POC demo.

Discussions in the mailing list.

Discussions in the IRC.

The Horizon patch set which depends on this functionality

Property Protections introduction in Glance