Support move operations with qos ports - Ussuri
Since microversion 2.72 nova supports creating servers with neutron ports having resource request. Since the Train release nova also supports cold migrating and resizing such servers. However other move operations like live migration, evacuation and unshelve are still not possible due to missing resource handling implementation in nova. The main content of this spec was previously proposed and approved in Train but only partially was implemented. So this spec proposes only the still missing pieces. Blueprint: support-move-ops-with-qos-ports-ussuri Change-Id: Ife73544f997c71f7840e0f772ca6a7870a8df69e
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Balazs Gibizer
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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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Server move operations with ports having resource request
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=========================================================
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https://blueprints.launchpad.net/nova/+spec/support-move-ops-with-qos-ports-ussuri
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Problem description
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===================
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Since `microversion 2.72`_ nova supports creating servers with neutron ports
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having resource request. Since the Train release nova also supports cold
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migrating and resizing such servers. However other move operations i.e. live
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migration, evacuation and unshelve after shelve offload are still not
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possible due to missing resource handling implementation in nova.
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Use Cases
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---------
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The admin needs to be able to request the same life-cycle operations
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for these servers as for any other servers.
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Proposed change
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===============
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To support live-migrate, evacuate and unshelve we will follow the
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implementation pattern that is described in the `Train spec`_ and then
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implemented for cold migrate and resize during the Train release.
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During the Train implementation the `compute RPC API`_ methods were extended
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with the necessary RequestSpec parameter for every move operation. So no
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further RPC change is expected during the implementation of this spec.
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During evacuate and unshelve operations the compute manager is responsible to
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update the port binding in neutron. These code paths will be extended to also
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update the allocation key in the port binding according to the allocation on
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the target host.
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During live-migrate nova uses the multiple bindings API of neutron to manage
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the bindings on the source and the target host in parallel. The conductor
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creates the new, inactive binding on the destination host in neutron and it
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will add the ``allocation`` key in the new binding according to the
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``RequestSpec``. When the live-migrate finishes the source port binding is
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deleted along with the source host allocation. If the live-migration is
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rolled back the source host binding still has the proper ``allocation`` key
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set.
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From the not-yet-supported move operations only live-migration has a reschedule
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loop. It is handled in the ``LiveMigrationTask`` in the super conductor.
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During reschedule the allocation key of the port binding of the neutron ports
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needs to be updated according to the new allocation on the newly selected
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target host.
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The multiple bindings neutron API extension cannot be turned off so if it is
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not present nova can fail the live-migrate operation if ports have resource
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request.
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Currently these move operations are rejected by nova if the server has ports
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attached with resource request. After the above proposed change is implemented
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these operations will be allowed. The way we will signal that nova is capable
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of supporting these operations is described in the `REST API impact`_ section.
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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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At the Train PTG we `agreed`_ to implement the support for the move operations
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as bugfixes without any new microversion. After the implementation is done the
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code that currently rejects the move operations are removed from the API and
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nova will accept and support these operations with any microversion.
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This is what we did with cold migrate and resize in Train and will follow that
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pattern in Ussuri.
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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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None
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Performance Impact
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------------------
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During move operations the conductor needs to query neutron to get the
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resource request of the ports that are attached to the server. Also, after the
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scheduling the request group - resource provider mapping needs to be
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recalculated and the binding:profile of the ports needs to be updated in
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neutron.
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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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As the solution depends on a minimum RPC version and as it requires compute
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manager changes the move operations can only be supported after both the
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source and the destination host are upgraded. So the conductor needs to ensure
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that the service version of both computes is high enough. However if the
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conductor is configured with ``[upgrade_levels]compute=auto``
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(e.g. rolling upgrade) or the compute RPC is manually pinned then even if both
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the source and the destination computes are new enough the destination compute
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may still not get the necessary information to perform the port binding update.
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Therefore an additional check is needed based on the actual RPC version used
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towards the destination compute. These checks will be similar to the ones that
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were implemented for `cold migration`_.
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The support for move operations makes it possible to heal missing or
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inconsistent port allocations as during the move the requested resources are
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re-calculated and the new allocation created accordingly in placement. This
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will complement `the port allocation healing capabilities`_ of the
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``nova-manage placement heal_allocations`` CLI that has multiple limitations in
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this regard.
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In general the operators having incomplete port allocations are recommended to
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try to heal that with the ``heal_allocations`` CLI in place if possible to
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minimize the number for server move operations required.
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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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balazs-gibizer
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Other contributors:
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None
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Core Liaison
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------------
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Core liaison:
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mriedem
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Work Items
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----------
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For each move operation:
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* Before scheduling, gather the requested resource from neutron and update
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the RequestSpec accordingly
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* After the scheduler selected the destination of the move operation calculate
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the resource provider - request group mapping and update the neutron port
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binding according to the destination allocation. This happens on the compute
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side for evacuate and unshelve but happens still in the conductor for live
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migration.
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* If there are SRIOV interfaces involved update the InstancePciRequest to drive
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the PCI resource claim on the destination compute to consume VFs from the
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same PF as the port resources are allocated from.
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For live migration the reschedule also needs to be handled in the super
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conductor.
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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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Each move operation will have a functional test asserting that the proper
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allocation exists after the move, old allocations are removed, and the port
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binding in neutron refers to the appropriate resource provider.
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For live migration reschedule also needs to be covered with functional tests.
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When the source compute is recovered the compute manager cleans up the
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evacuated instances. We need test coverage to make sure that the bandwidth
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allocation is cleaned up from the source host but the neutron port binding is
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not changed as it is expected to already point to the target host allocation.
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Documentation Impact
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====================
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The API guide `Using ports with resource request`_ will be updated accordingly.
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Also the Limitations section of the neutron admin guide
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`Quality of Service Guaranteed Minimum Bandwidth`_ needs to be updated.
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References
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==========
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.. _`bandwidth resource provider spec`: https://specs.openstack.org/openstack/nova-specs/specs/stein/implemented/bandwidth-resource-provider.html
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.. _`Train spec`: https://specs.openstack.org/openstack/nova-specs/specs/train/approved/support-move-ops-with-qos-ports.html
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.. _`microversion 2.72`: https://docs.openstack.org/nova/latest/reference/api-microversion-history.html#maximum-in-stein
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.. _`Using ports with resource request`: https://docs.openstack.org/nova/latest/admin/port_with_resource_request.html
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.. _`Quality of Service Guaranteed Minimum Bandwidth`: https://docs.openstack.org/neutron/latest/admin/config-qos-min-bw.html
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.. _`ML thread`: http://lists.openstack.org/pipermail/openstack-discuss/2019-January/001881.html
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.. _`the port allocation healing capabilities`: https://review.openstack.org/#/c/637955
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.. _`agreed`: http://lists.openstack.org/pipermail/openstack-discuss/2019-May/005807.html
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.. _`cold migration`: https://github.com/openstack/nova/blob/4d034b79eb4483848fa8346149d0387af4eeaa2a/nova/conductor/tasks/migrate.py#L383
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.. _`compute RPC API`: https://github.com/openstack/nova/blob/4d034b79eb4483848fa8346149d0387af4eeaa2a/nova/compute/rpcapi.py#L367
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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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* - Ussuri
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- Updated to show the remaining scope for Ussuri.
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