Specifying az when restore shelved server
This spec proposes support admin/user to specify ``availability_zone`` to unshelve a shelved server. APIImpact Blueprint: support-specifying-az-when-restore-shelved-server Change-Id: I0d4855c100a43548019cd0330ec325ba8b8c686d
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zhangbailin
Matt Riedemann
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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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Support specifying az when restore shelved server
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=================================================
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https://blueprints.launchpad.net/nova/+spec/support-specifying-az-when-restore-shelved-server
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This blueprint proposes support admin/user to specify ``availability_zone``
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to unshelve a shelved server.
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Problem description
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===================
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If the current instance is in the ``SHELVED_OFFLOADED`` status, then its
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``availability_zone`` attribute will be set to None in the ``instances``
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database table (this change comes from [1]_). But the ``spec`` attribute
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records the value of the AZ of the instance before being shelved in the
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``request_specs`` database table. When unshelve the server, the value of
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AZ will be taken from ``spec`` as 'instance.availability_zone'.
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There are two ways an instance can be in an AZ::
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1. The user passes an AZ on server create or
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2. [DEFAULT]/default_schedule_zone is set.
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For the above two cases, the RequestSpec.availability_zone will always remain
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in the user-specified or [DEFAULT]/default_schedule_zone AZ, even if the AZ is
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later renamed and [DEFAULT]/default_schedule_zone is changed, or that server
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is on shelve/unshelve, there is a related bug here [2]_.
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Once the AZ in ``spec`` is missing, unshelve server will have an error.
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Use Cases
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---------
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As a administrator/user, I want to specify AZ when executing unshelve/restore
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a shelved-offloaded server.
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Proposed change
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===============
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Add a new microversion to the unshelve/restore shelved server
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(unshelve Action) API to support specifying AZ to restore a shelved server.
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If the operator configures cross_az_attach=True [3]_ in nova.conf, in the
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[cinder] group, the server create flow will fail if the specified AZ does
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not match the volumes being attached to the server. Unshelve should likely
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also fail for the same reason, but to figure that out we'd have to iterate
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the volumes (via BDMs) attached to the server and determine if their AZ
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matches the user-specified AZ and if not, fail the unshelve request, this
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needs to be checked as an edge case in the API.
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Add ``availability_zone`` attribute to unshelve Action request body.
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The availability_zone parameter for unshelve will just be an availability zone,
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not the `ZONE:HOST:NODE`_ (admin-only) format available during server create
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which, when HOST and/or NODE are specified, will forcefully bypass the
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scheduler.
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Alternatives
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------------
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Creating a server from the shelved snapshot image in another AZ (or just avoid
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shelve/unshelve altogether and snapshot the server, delete it, and then create
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with the new AZ). The downside is you lose the ports/volumes you had connected
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to the previous server.
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Another alternative is the AZ rename/delete code could be changed to prevent
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renaming/deleting an AZ while there are shelved offloaded servers that were
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created in that AZ. This, however, would not be scalable because we'd have to
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get and deserialize every RequestSpec for every ``SHELVED_OFFLOADED`` server
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just to see if it had a matching AZ.
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In other words, because the RequestSpec is a serialized json string in the
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database, we cannot do a simple DB query to efficiently get this information.
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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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* URL:
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* /v2.1/servers/{server_id}/action
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* Request method:
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* POST
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The availability zone data will be able to add to request payload ::
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{
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"unshelve": {
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"availability_zone": 'beijing'
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}
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}
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The ``availability_zone`` field is optional.
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If the server status is 'SHELVED' rather than 'SHELVED_OFFLOADED' and an AZ
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is specified the API will return a 400 response, otherwise if my server was
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created in AZ1, I shelved it (but didn't offload it yet), and then unshelved
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and specified AZ2 but the server doesn't end up in AZ2, this request will be
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ignored, because of that will be start instance directly. So this change only
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supports the case where the server status is 'SHELVED_OFFLOADED'.
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Security impact
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---------------
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None
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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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The python-novaclient and python-openstackclient will be updated.
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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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Upgrade 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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Brin Zhang
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Work Items
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----------
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* Add a new microversion to the unshelve/restore shelved server
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(unshelve Action) API
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* Add related tests
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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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* Add related unit tests
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* Add related functional tests
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Documentation Impact
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====================
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Add docs that mention unshelve/restore shelved server after the microversion.
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References
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==========
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.. [1] https://review.opendev.org/#/c/599087/
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.. [2] https://bugs.launchpad.net/nova/+bug/1723880
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.. [3] https://docs.openstack.org/nova/latest/configuration/config.html#cinder.cross_az_attach
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.. _ZONE:HOST:NODE: https://docs.openstack.org/nova/latest/admin/availability-zones.html
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History
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=======
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.. list-table:: Revisions
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:header-rows: 1
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* - Release Name
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- Description
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* - Train
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- Introduced
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