Merge "Per-instance serial number (spec)"
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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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Per-instance serial number
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==========================
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Add support for providing unique per-instance serial numbers to servers.
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Problem description
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===================
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A libvirt guest's serial number in the machine BIOS comes from the
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``[libvirt]/sysinfo_serial`` configuration option [1]_, which defaults to
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reading it from the compute host's ``/etc/machine-id`` file or if that does
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not exist, reading it from the libvirt host capabilities. Either way, all
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guests on the same host have the same serial number in the guest BIOS.
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This can be problematic for guests running licensed software that charges per
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installation based on the serial number because if the guest is migrated, it
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will incur new charges even though it is only running a single instance of the
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software.
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If the guest has a specific serial unique to itself, then the license
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essentially travels with the guest.
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Use Cases
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---------
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As a user (or cloud provider), I do not want workloads to incur license
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charges simply because of those workloads being migrated during normal
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operation of the cloud.
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Proposed change
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===============
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To allow users to control this behavior (if the cloud provides it), a new
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flavor extra spec ``hw:unique_serial`` and corresponding image property
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``hw_unique_serial`` will be introduced which when either is set to ``True``
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will result in the guest serial number being set to the instance UUID.
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For operators that just want per-instance serial numbers either globally
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or for a set of host aggregates, a new "unique" choice will be added to the
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existing ``[libvirt]/sysinfo_serial`` configuration which if set will result
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in the guest serial number being set to the instance UUID. Note that the
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default value for the option will not change as part of this blueprint.
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The flavor/image value, if set, supersedes the host configuration.
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Alternatives
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------------
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We could allow users to pass through a serial number UUID when creating
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a server and then pass that down through to the hypervisor, but that seems
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somewhat excessive for this small change. It is also not clear that all
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hypervisor backends support specifying the serial number in the guest and we
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want to avoid adding API features that not all compute drivers can support.
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Allowing the user to specify a serial number could also potentially be abused
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for pirating software unless a unique constraint was put in place, but even
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then it would have to span an entire deployment (per-cell DB restrictions would
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not be good enough).
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Data model impact
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-----------------
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None besides a new ``FlexibleBooleanField`` field being added to the
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``ImageMetaProps`` object.
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REST API impact
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---------------
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None
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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. Users can leverage the functionality by creating new servers with an
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enabled flavor/image, or rebuild/resize existing servers with an enabled
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flavor/image.
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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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Operators that wish to expose this functionality can do so by adding the
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extra spec to their flavors and/or images or setting
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``[libvirt]/sysinfo_serial=unique`` in nova configuration. If they want to
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restrict the functionality to a set of compute hosts, that can also be done by
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restricting enabled flavors/images to host aggregates.
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Developer impact
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----------------
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None, except maintainers of other compute drivers besides the libvirt driver
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may wish to support the feature eventually.
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Upgrade impact
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--------------
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There is not an explicit upgrade impact except that obviously older compute
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code would not know about the new flavor extra spec or image property and thus
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if a user was requesting a server with the property, but the serial in the
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guest did not match the instance UUID, they could be confused about why it
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does not work. Again, operators can control this by deciding when to enable
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the feature or by restricting it to certain host aggregates.
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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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Zhenyu Zheng <zhengzhenyu@huawei.com> (Kevin_Zheng)
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Other contributors:
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Matt Riedemann <mriedem.os@gmail.com> (mriedem)
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Work Items
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----------
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* Add the ``ImageMetaProps.hw_unique_serial`` field.
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* Add a new choice, "unique", to the ``[libvirt]/sysinfo_serial`` configuration
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option.
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* Check for the flavor extra spec and image property in the libvirt driver
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where the serial number config is set.
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* Docs and 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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Unit tests should be sufficient for this relatively small feature.
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Documentation Impact
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====================
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* The flavor extra spec will be documented: https://docs.openstack.org/nova/latest/user/flavors.html
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* The image property will be documented: https://docs.openstack.org/glance/latest/admin/useful-image-properties.html
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* The new configuration option choice will be documented [1]_
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References
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==========
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.. [1] https://docs.openstack.org/nova/latest/configuration/config.html#libvirt.sysinfo_serial
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* Libvirt documentation: https://libvirt.org/formatdomain.html#elementsSysinfo
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* Nova meeting discussion: http://eavesdrop.openstack.org/meetings/nova/2018/nova.2018-10-18-14.00.log.html#l-199
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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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* - Stein
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- Introduced
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