Copy volume to image in multiple stores of glance

Change-Id: Ic7f259c3af6bd691e6d24ed180430e760d28eba8
Implements: copy-image-in-multiple-stores

specs/ussuri/copy-image-in-multiple-stores.rst

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+..
+ This work is licensed under a Creative Commons Attribution 3.0 Unported
+ License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+
+=================================================
+Copy volume to image in multiple stores of glance
+=================================================
+
+https://blueprints.launchpad.net/cinder/+spec/copy-image-in-multiple-stores
+
+This specs propose to send base image reference to glance on volume
+upload to image API.
+
+Problem description
+===================
+
+In Train, Glance has added the ability to configure multiple stores
+[1]_. This way an operator can configure more than one of similar or
+different kind of stores and use one as a default store. If a store
+is not specified at the time of uploading an image then the image
+will be stored in default store.
+
+In Train, I have proposed a spec [2]_ where cinder can specify the glance
+store via the volume-type. The store specified in volume-type will be
+passed to glance using `x-image-meta-store` header. Even operator
+specifies the glance store identifier in volume-type it will only allow
+volume image to be uploaded to single specified store and does not allow
+for co-location of the image. Also, it depends on the operator configuring
+the volume-type extra-specs to define a preferred Glance store; if the
+operator doesn't take this step, all uploads go to the default Glance store.
+
+Use Cases
+=========
+
+1. At the moment, if cloud provider decided to upgrade their cloud to Train
+   release to use the ability of glance of configuring multiple store and the
+   base image from which volume is created resides in multiple stores
+   of glance, then if the operator has not defined a glance store in the
+   volume-type extra specs, the image created from volume will always
+   be uploaded to default store and there is no way to replicate/copy these
+   image bits to all the stores where base image is uploaded. As a result,
+   operators today need to perform a number of manual steps in order
+   to replicate/copy image bits on glance stores despite using the
+   'enabled_backends' configuration option. For this purpose, he/she need
+   to manually copy the newly created image from volume in all stores and
+   register these others locations URL with the image using the glance API.
+
+Proposed change
+===============
+
+When a volume is created from an image, Cinder currently stores the
+image_uuid in the volume_image_metadata. When Cinder upload volume to
+image is requested cinder should pass the 'image_uuid' as a header
+'x-openstack-base-image-ref' to glance, so that glance can identify the
+store(s) in which the original image is located. Cinder is also storing
+this glance store information in volume types [2]_, where the store
+identifier associated with volume-type will be passed as a header
+'x-image-meta-store' to glance to upload the image created from volume to
+that specific store.
+
+If a volume is created from an image and Cinder passes both the
+'x-image-meta-store' and 'x-openstack-base-image-ref' headers, Glance will
+ignore the 'x-openstack-base-image-ref' header and will use the store_id
+specified in the 'x-image-meta-store' header.
+
+If volume is not bootable and store information is available in
+volume type then glance will use store associated with volume type to upload
+the image created from volume.
+
+If volume is not bootable and store information is not available in
+volume type then glance will use 'default store' to upload the image
+created from volume.
+
+Alternatives
+------------
+
+Continue with passing store information using volume types [2]_.
+
+Data model impact
+-----------------
+
+None
+
+REST API impact
+---------------
+
+None
+
+Security impact
+---------------
+
+None
+
+Active/Active HA impact
+-----------------------
+
+None
+
+
+Notifications impact
+--------------------
+
+None
+
+Other end user impact
+---------------------
+
+None
+
+Performance Impact
+------------------
+
+None
+
+Other deployer impact
+---------------------
+
+None
+
+Developer impact
+----------------
+
+None
+
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  whoami-rajat
+
+Other contributors:
+  abhishek-kekane
+
+Work Items
+----------
+
+* Pass image uuid stored in 'volume_image_metadata' as header to glance
+* Add related tests
+
+
+Dependencies
+============
+
+* Depends on implementation of 'Support Glance multiple stores' [2]_.
+
+
+Testing
+=======
+
+* Add related unittest
+* Add related functional test
+* Add tempest tests
+
+
+Documentation Impact
+====================
+
+Operators documentation should be updated according to spec implementation.
+
+
+References
+==========
+
+.. [1] https://docs.openstack.org/glance/rocky/admin/multistores.html
+.. [2] http://specs.openstack.org/openstack/cinder-specs/specs/train/support-glance-multiple-backend.html