4c147f1d6b
This patch moves all specs that were implmented in the ussuri release and sets up the redirects accordingly. Change-Id: I7eddfab1d3b6aa5a23f47b6d8966760ca5648faa
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186 lines
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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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Virtual instance rescue with boot from volume instances
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=======================================================
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https://blueprints.launchpad.net/nova/+spec/virt-bfv-instance-rescue
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Building on the existing stable disk device rescue spec [1]_ this spec will
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introduce support for rescuing boot from volume (BFV) instances and detail the
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impact this will have on the API.
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Problem description
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===================
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The original instance rescue implementation included a check in the compute API
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to block any requests to rescue instances where the root BDM is a cinder volume
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[2]_. Any such request would be rejected initially by an
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``InstanceNotRescuable`` exception being raised back to the API that would then
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result in a ``400`` error being returned to the caller.
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Given the work being carried out as part of the stable disk device rescue spec
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[1]_ we are now able to correctly wire up all disks during an instance rescue
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and as a result can remove this check, accepting requests to rescue BFV
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instances.
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Use Cases
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---------
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* Tenant users would like to rescue BFV instances.
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Proposed change
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===============
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The work outlined in the stable disk device rescue spec [1]_ will already allow
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Nova to correctly wire up root cinder volumes during a rescue while booting
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from the rescue device.
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The only additional changes required to allow us to remove the current BFV
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instance check from the compute API are a new compatibility trait, update to
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``_get_rescue_image`` within the compute manager and a new API microversion.
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A new ``COMPUTE_RESCUE_BFV`` trait will be introduced to os-traits, allowing a
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compatibility check within the compute API to ensure the target compute service
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is capable of rescuing BFV instances.
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In the compute manager ``_get_rescue_image`` will be extended to attempt to
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find a reference to the original image when a rescue image is not provided but
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the instance is BFV. An ``InstanceNotRescuable`` exception will be raised if no
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reference to the original can be found as we can't boot from the original root
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disk as a rescue device while also attaching it again to the instance during a
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rescue.
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A new API microversion will be introduced to signal the change in behaviour
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from the existing rescue implementation where attempts to rescue BFV instances
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were rejected.
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Alternatives
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------------
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None
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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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A new microversion will be introduced to signal the change in behaviour from
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the original implementation. No other changes will be made to the API.
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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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Users attempting to use this feature will need to opt-in by using the newly
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introduced microversion or later.
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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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The ``COMPUTE_RESCUE_BFV`` compatibility trait will be used to ensure the
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target compute service is capable of performing the requested rescue against a
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BFV instance within the compute API. If this is not set the existing
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``InstanceNotRescuable`` exception will be raised back to the API resulting in
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a ``400`` error being returned to the caller.
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The new microversion or later will be used by callers to opt-in to this new
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behaviour. If this isn't provided the original behaviour of rejecting requests
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to rescue BFV instances will be used.
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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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lyarwood
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Other contributors:
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Feature Liaison
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---------------
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lyarwood
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Work Items
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----------
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* Complete the initial stable device rescue spec. [1]_
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* Introduce a new ``COMPUTE_RESCUE_BFV`` trait to os-traits
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* Start reporting this trait from Nova's Libvirt driver.
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* Introduce a new microversion signalling the API behaviour change.
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* Start using the new ``COMPUTE_RESCUE_BFV`` trait and microversion in the REST
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API to determine when to allow the Compute API to rescue a BFV instance.
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Dependencies
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============
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As highlighted throughout this spec this all requires the initial stable disk
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device rescue spec [1]_ to land before this could be implemented.
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Testing
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=======
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Tempest and functional tests will be introduced to fully validate this new
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behaviour.
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Documentation Impact
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====================
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The new microversion will be documented and the existing rescue API
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documentation updated to reference it.
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References
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==========
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.. [1] Virtual instance rescue with stable disk devices https://review.opendev.org/#/c/693849/
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.. [2] BFV instance compute API check https://github.com/openstack/nova/blob/7aa88029bbf6311033457c32801963da01e88ecb/nova/compute/api.py#L4044-L4053
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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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* - Ussuri
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- Introduced
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