Merge "[APIImpact] Add a new glance-download import method"
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specs/zed/approved/glance/glance-download-import.rst
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specs/zed/approved/glance/glance-download-import.rst
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..
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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=============================================================================
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Add new import method to support downloading image from another glance/region
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=============================================================================
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https://blueprints.launchpad.net/glance/+spec/glance-download-import
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This spec describe a new import method called glance-download that implements a
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glance to glance download in a multi-region cloud with a federated Keystone.
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Problem description
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===================
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When dealing with a multi-region cloud it often appears that operators or
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customers need to copy images from a region to another, for example:
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* Copy all your public images between your regions (operator)
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* Copy instance snapshot in another region to have a backup (user)
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* Build your base application image from a factory in one region, then
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propagate it to multiple regions (user)
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We can't rely on the "copy-image" import method to copy an image from a
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backend to another because it requires the same glance endpoint in the same
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region which is not our use-case here.
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The only way we have to do it now is to locally download the image data and
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upload it elsewhere, which requires some orchestration, and is a huge disk
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space and bandwidth loss.
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Proposed change
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===============
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Implement an internal plugin called glance-download based on the existing
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internal plugin web-download that will import an image stored on a remote
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glance. The web-download workflow will remain unchanged, the only difference
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is to retrieve the downloadable data from an other glance endpoint instead of
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from an arbitrary URL.
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We should note several things:
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* To authenticate on the remote glance we propose to use the context token
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of the call, so it will require a federated Keystone environment between
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the two Glance.
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* The creation of the image must be handled by the end user as for the
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web-download plugin meaning that it is the responsibility of the user to
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take care of disk format, container format and metadata of the newly
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created image.
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If necessary, the plugin will update the container_format and disk_format
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to match what is set on source glance.
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* The plugin will come with an extra task in the taskflow that will be in
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charge of setting the container_format and disk_format to be the same as it
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is on the source glance. It will also copy some extra properties defined in
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the extra_properties_prefixes option of glance_download_properties section.
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The default extra_properties_prefixes values are 'hw\_', 'trait:', 'os_distro',
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'os_secure_boot' and 'os_type' which are needed to ensure an instance can boot
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on the image. An operator will be able to remove or add other extra
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properties by modifying this configuration variable.
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This extra_properties_prefixes is a list of prefixes, meaning that all the
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metadata that are starting with a prefix belonging to that list will be
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copied.
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.. code-block:: ini
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[glance_download_properties]
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extra_properties_prefixes = [
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'hw_',
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'trait:',
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'os_distro',
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'os_secure_boot',
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'os_type'
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]
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..
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* If metadata injection is configured on the target glance it will override
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the metadata as the injection is run after the import.
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Alternatives
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------------
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We could imagine a take out alternative where the owner of the image in the
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source cloud generates a limited-use tokenized URL that allows access to the
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image without any keystone auth. Such solution is more risky as we do not
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have any authentication mechanism to access the remote image. It will also
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require rewriting the code as there is no existing source.
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This would also require developing a mechanism to manage creation and
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expiration of the temporary urls which would result in a more complex solution
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that requires more time to develop, document and test.
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Data model impact
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-----------------
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None
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REST API impact
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---------------
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Modification of existing API resource
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* Resource **/v2/images/<image id>/import**
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* Method: **POST**
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* Common response code:
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* *201*: import job queued
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* *400*: bad request with details
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* *401*: Unauthorized
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* *403*: Forbidden
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* JSON body definition
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.. code-block:: javascript
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"method": {
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"name": {
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"description": "Name of the method used, here is glance-download",
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"type": "string"
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},
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"glance_image_id": {
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"description": "The image id to download on remote glance",
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"type": "string"
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},
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"glance_region": {
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"description": "The region name of remote glance",
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"type": "string"
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},
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"glance_service_interface": {
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"decription": "The interface of remote glance, default to 'public'",
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"type": "string"
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}
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}
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..
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Example:
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.. code-block:: javascript
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"method": {
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"name": "glance-download",
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"glance_image_id": "02ea04ba-72b3-4687-810d-8ba10c991a97",
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"glance_region": "REGION1",
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"glance_service_interface": "admin"
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}
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..
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Security impact
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---------------
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We use the token of the request to authenticate on remote glance. As we are in
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multi-region context with a federated keystone, there is no security impact.
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Notifications impact
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--------------------
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None
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Other end user impact
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---------------------
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Users will have a new import mechanism open to them, after updating their
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client
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Performance Impact
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------------------
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None
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Other deployer impact
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---------------------
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None
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Developer impact
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----------------
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None
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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pslestang
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Other contributors:
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alistarle
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Work Items
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----------
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* glance:
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* Create a base download class that will be inherited by web-download and
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glance-download
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* Patch the web-download class to inherit from base download class
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* Write the glance-download class
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* Patch the api image import to support the glance-download method
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* Add in task flow a class in charge of:
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* setting the correct container_format and disk_format
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* copying the metadatas defined in extra_properties option of the
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glance_download_properties section. Default list must be
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['hw\_', 'trait:', 'os_distro', 'os_secure_boot', 'os_type']
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* The class has to be added to taskflow as a normal task to be reusable if
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needed. We only have to check for input parameters to know if it can be
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run or not.
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* Add the glance-download internal plugin in setup
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* write unit/functional tests
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* update documentation
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* glance and openstack client
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* add support for glance-download method
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* update documentation
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Dependencies
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============
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None
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Testing
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=======
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* Unit and functional tests in Glance
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* Tempest tests. Testing glance-download plugin with the g-api-r separate
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endpoint looks good even if it shares the same database to validate the
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workflow.
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Documentation Impact
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====================
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The documentation needs to be updated to identify this new import method
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References
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==========
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* https://review.opendev.org/c/openstack/glance/+/840318
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