glance-specs/specs/mitaka/implemented/cinder-store-upload-download.rst

Support download from and upload to Cinder volumes

https://blueprints.launchpad.net/glance/+spec/cinder-store-upload-download

Current Glance's Cinder backend driver only can get the volume size but doesn't support read, write and deletion of volumes.

As missing parts in Cinder side (listed in¹: os-brick library, readonly-volumes, multi-attach) are now supported, now we can implement read (download), write (upload), and deletion for it.

When an raw image is backed on the cinder store, a new volume with the image can be created by cloning the image volume. This will be useful to launch boot-from-volume instances rapidly as some Cinder drivers can clone a volume efficiently using copy-on-write. It will also improves storage capacity with the drivers which support thin-provisioning.²

Note that the image volume itself is not intended to be used as a boot-volume for an instance. Image volumes are marked read-only, so they cannot be attached to instances in read-write mode. Instead, cloned volumes should be used for booting instances.

Problem description

Without upload, download and deletion support of Glance's Cinder backend driver, it can't be used as a default store.

Proposed change

This spec proposes implementing image uploading to and downloading from Cinder volumes, and deletion of the volume on the image deletion.

• Uploading steps:

  • Create a new volume with the size that can store the image. It will be placed in the tenant specified in glance-api.conf.

  • Attach the new volume to the glance-api host using the os-brick library.

    • The os-brick library collects the connector (host) information, such as the initiator IQN for iSCSI or WWN for FibreChannel.
    • Call initialize_connection API of Cinder with the connector information and the volume as arguments to get the volume connection information, such as target portal IP address and IQN for iSCSI.
    • Pass the connection information to the os-brick's connect_volume method to attach the volume to the host. The volume device information such as the device path (e.g. /dev/sdX) is returned. This step requires root privilege to execute the command for iSCSI, FC and so on, so the glance-rootwrap must be installed and it should allow the commands for os-brick.³

  • Write the image data to the volume from the given device path.

  • Detach the volume from the host.

    • Call the os-brick's disconnect_volume method and Cinder's terminate_connection API to remove the volume connection.

  • Mark the volume as read-only.

  • Add volume metadata that indicate the image size, image ID, image owner (to track the owner even when it is placed in the service tenant). e.g.: :

    {
     'image_id': 'e38f5596-4bd3-4b63-b4ef-88bcc814ed8e',
     'image_owner':     'b58fffa08b4242988c42950b5f24fcd5',
     'image_size':      '228599296',
    }

• Downloading steps:
  • Attach the image volume to glance-api host as read-only.
  • Read the image data from the volume.
  • Detach the volume.
• Deletion steps:
  • Call the Cinder's delete API to delete the volume when the image is deleted.

As cinder currently doesn't support ACL or public volumes among tenants, in order to support public or sharable images, the image volume should be placed in the service tenant which is only accessible from the Glance and Cinder services to control the accessibility.

Alternatives

None

Data model impact

None

REST API impact

None

Security impact

To attach and detach volumes to the host, root privilege is required to operate block devices on the host. Glance needs to import oslo-rootwrap to allow only required commands for these operations to be executed as root.

The Glance node must be a part of storage network (iSCSI, FC etc.). In theory that might open new attack vectors each way.

Notifications impact

None

Other end user impact

None

Performance Impact

When creating a new Cinder volume from an image stored in the Glance Cinder store, or creating a new image from a volume, Cinder is able to offload the image copy using storage array features such as background copy or copy-on-write, if some conditions (e.g. image stored in Cinder backend is in raw format) are satisfied. This will improve the performance of image copy significantly.

Nova-compute will be able to bypass the image copy by attaching the image volumes to the host, if Cinder is deployed.

Note that the image upload/download requires sufficient bandwidth to/from cinder storage.

Other deployer impact

To use cinder backends, the Glance node must be able to access the backend storage and it may require additional hardware connectivity (iSCSI, FC, etc.). Operators have to configure cinder and glance-api.conf appropriately.

• To enable cinder store, cinder must be added to the stores option in the glance-api.conf.
• To place the image volume into the specific tenant, authentication information for the tenant must also be provided.
• The glance-rootwrap must be installed. The rootwrap config path should also be configured in glance-api.conf.
• To offload the image copy on volume creation to the storage array, the allowed_direct_url_schemes option should contain cinder in cinder.conf.⁴ Also, the glance-api host must be able to attach the Cinder volumes onto itself.

Developer impact

None

Implementation

Assignee(s)

Primary assignee:

tsekiyam

Reviewers

Core reviewer(s):

flaper87

Work Items

• Import os-brick and oslo-rootwrap into glance_store.
• Extend current cinder backend driver to support upload, download and deletion.

Dependencies

None

Testing

• Enable cinder backend in the devstack.
• Test uploading of an image to the cinder backend.
• Then test downloading of the image again.
• Delete the image and check if the volume is deleted.
• Test the other normal glance store operations such as owner changes and sharing.

Documentation Impact

The documentation should be expanded to describe how to enable and use cinder store. Especially, it should explain new options to configure cinder authentication (tenant id, username, password) to store the volume into the specific tenant.

It also needs to cover the requirement to Glance node being the part of storage network (iSCSI, FC etc.) and having sufficient bandwidth towards the storage.

References

---

1. Blueprint: Adding a store driver to allow Cinder as a block storage backend for Glance: https://blueprints.launchpad.net/glance/+spec/glance-cinder-driver↩︎

2. Cloud Administrator Guide: Volume-backed image: http://docs.openstack.org/admin-guide-cloud/blockstorage_volume_backed_image.html↩︎

3. Rootwrap filter for os-brick: https://github.com/openstack/os-brick/blob/master/etc/os-brick/rootwrap.d/os-brick.filters↩︎

4. Cloud Administrator Guide: Volume-backed image: http://docs.openstack.org/admin-guide-cloud/blockstorage_volume_backed_image.html↩︎