Add "disable local disks" option to flavors
This feature adds the possibility to define a flavor, that does not create any ephemeral disks locally on the hypervisor. If the new flavor key 'local_disks' is set to 'False', users are "forced" to create a bootable volume to launch an instance from that flavor. APIImpact DocImpact Change-Id: I52b8d473d86ce471e61a2c3505f6c274ad0643b8 Implements: blueprint flavor-root-disk-none
This commit is contained in:
Tom Patzig
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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 support for flavors with no local ephemeral disks
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=====================================================
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https://blueprints.launchpad.net/nova/+spec/flavor-root-disk-none
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This feature adds the possibility to define a flavor,
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that does not create any ephemeral disk locally on the hypervisor.
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The proposal is to add a new flavor key ``local_disks``.
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If ``local_disks`` is set to ``False``, no hypervisor-local root disk
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or any other local ephemeral disk will be created.
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A bootable volume needs to be created to launch an instance
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from that flavor. All other additional disks can only be volume-based,
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as well.
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Problem description
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===================
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Currently there is no way to force root disk being on cinder and having
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no hypervisor-local ephemeral disks at all.
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Setting ``root_gb`` to 0 defaults in creating an ephemeral root disk
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with the size of the glance image.
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We do not want to have ephemeral disks locally on the hypervisor;
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not on a local filesystem nor on a share mounted to /var/lib/nova/instances.
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As these shares grow, they become unmaintainable and performance gets worse.
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Storing the ephemeral root disk in the hypervisor's local filesystem is also
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not a good idea, since consumer data on the root disk often cannot simply
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be deleted.
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Having more or less all block devices in cinder volumes gives us a unique
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and flexible feature set for maintaining block storage of instances and
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the instances themselves.
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Use Cases
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---------
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The use case for End Users is to not create ephemeral (root) disks locally on
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the hypervisor by accident.
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When launching an instance from a flavor with disabled local disks,
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the user will be informed to create a bootable volume in order to launch
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the instance with that volume. The volume can be an existing one or a new
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one, created upon the instance launch request via the block-device parameter.
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The end user does not need to worry about disk placement; which impacts
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instance migration, data persistence/loss, and/or shared storage performance.
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The use case for deployers is to have the ability to prevent customers
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from creating ephemeral (root) disks locally on the hypervisor. Deployers do
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not have to worry to much about local HV filesystem sizing nor they do not
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need to create one big share for /var/lib/nova/instances, which gets mounted on
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all hypervisors. As that share grows it gets unmaintainable and performance is
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gets worse. They do not have to deal with customer data loss on ephemeral
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disks, stored on local hypervisor FS, in case of hypervisor outage.
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Proposed change
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===============
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The scope of the change:
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* new flavor key ``local_disks`` in the API
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* new boolean column ``local_disks`` for table flavors
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* default value for ``local_disks`` is True
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* older microversions display value of 0 for ``root_gb``, ``ephemeral_gb`` and
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``swap_gb``, if ``local_disks=False``
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* newer microversions do not return the keys ``root_gb``, ``ephemeral_gb`` and
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``swap_gb``, if ``local_disks=False``
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* if ``local_disks=False`` is given ``root_gb``, ``ephemeral_gb`` and
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``swap_gb`` are optional
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* if ``local_disks=False`` is given ``root_gb``, ``ephemeral_gb`` and
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``swap_gb`` are automatically set to 0, given values get ignored
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* if ``local_disks`` is omitted or set to True, ``root_gb`` is mandatory again
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* error, when flavor create request with ``local_disks=False`` and
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``root_gb`` > 0 and/or ``emphemeral_gb`` > 0 and/or ``swap_gb`` > 0
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* return descriptive exception, when flavor with ``local_disks=False`` and
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requested image larger than given blockdevice layout
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* return descriptive exception, when flavor with ``local_disks=False`` and
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given block_device parameter includes ``dest_type`` 'local'
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* return descriptive exception, when resizing instance from flavor with
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``local_disks=True`` to flavor with ``local_disks=False``
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* adjust api doc to include detailed description of ``local_disks`` key
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* config-drive will not be touched by that change, config-drive will still
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reside on local HV disks, like libvirt.xml and console.log do
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Alternatives
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------------
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The alternative is to always boot instances with the additional block_device
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parameter and ``dest_type`` 'volume', to make sure (root) disks are on cinder
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volumes and no hypervisor-local ephemeral disk gets created.
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But this has the downside, that someone might forget it and ephemeral disks
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get created locally on the HV.
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There is no way to force users, that no ephemeral root disks are being created
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on the hypervisor.
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Data model impact
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-----------------
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* add new column ``local_disks`` type boolean to flavor table (default is True)
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REST API impact
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---------------
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* introduce new api microversion which allows 'None' as disk value
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* POST v2.1/<tenant_id>/flavors:
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::
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{
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"flavor": {
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"name": "flavor_without_local_ephemeral_disks",
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"ram": 1024,
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"vcpus": 2,
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"local_disks": false,
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}
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}
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* flavor show omits ``root_gb``, ``ephemeral_gb`` and ``swap_gb``,
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when ``local_disks=False``:
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::
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{
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"flavor": {
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"OS-FLV-DISABLED:disabled": false,
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"local_disks": false,
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"os-flavor-access:is_public": true,
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"id": "1",
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"links": [
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{
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"href": "http://openstack.example.com/v2.1/openstack/flavors/1",
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"rel": "self"
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},
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{
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"href": "http://openstack.example.com/openstack/flavors/1",
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"rel": "bookmark"
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}
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],
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"name": "m1.tiny",
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"ram": 512,
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"vcpus": 1
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}
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}
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* with older microversions, ``root_gb``, ``ephemeral_gb`` and ``swap_gb`` will
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be returned with value 0, when ``local_disks=False``:
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::
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{
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"flavor": {
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"OS-FLV-DISABLED:disabled": false,
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"local_disks": false,
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"disk": 0,
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"OS-FLV-EXT-DATA:ephemeral": 0,
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"os-flavor-access:is_public": true,
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"id": "1",
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"links": [
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{
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"href": "http://openstack.example.com/v2.1/openstack/flavors/1",
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"rel": "self"
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},
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{
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"href": "http://openstack.example.com/openstack/flavors/1",
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"rel": "bookmark"
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}
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],
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"name": "m1.tiny",
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"ram": 512,
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"swap": 0,
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"vcpus": 1
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}
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}
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* ``root_gb`` is no longer mandatory with ``local_disks=False``
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* return 400 error when flavor has ``local_disks=False`` and no BD mapping
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given
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* return 400 error when flavor has ``local_disks=False`` and ``dest_type``
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local given in BD mapping
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* return 400 error when flavor has ``local_disks=True`` and instance resize to
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flavor ``local_disks=False`` requested
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* return 400 error on flavor create, when ``local_disks=False`` and ``root_gb``
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and/or ``ephemeral_gb`` and/or ``swap_gb`` given
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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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End users need to provide a proper blockdevice mapping with ``dest_type``
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volume, in order to use a flavor with ``local_disks=False``.
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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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If a deployer doesn't want any ephemeral/local disk on the hypervisor nodes,
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they just create flavors with ``local_disks=False`` and then all users of that
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cloud have to provide a blockdevice mapping with ``dest_type`` 'volume' when
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creating an instance.
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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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tpatzig
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Work Items
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----------
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* create db column
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* create api microversion with new key
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* support ``local_disks=False`` for flavor show
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* exception handling if ``local_disks=False`` in flavor and request contains
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local BD mapping
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* adjust flavor unit test
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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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* Create flavor with ``local_disks=False``
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* Boot instance with such flavor without volume
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* Boot instance with such flavor with local BD mapping
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* Boot instance with such flavor with volume
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Documentation Impact
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====================
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http://docs.openstack.org/openstack-ops/content/flavors.html
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API doc will be updated to include the new flavor option ``local_disks``.
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References
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==========
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None
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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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* - Newton
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- Introduced
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