Libvirt driver domain metadata
Metadata will be recorded in the libvirt domain XML configuration to provide information about the Nova instance that the domain corresponds to. The aim is to provide information that can be useful to administrators troubleshooting compute hosts. Change-Id: I2d58b1029f27a0e090f27ded391913e42d163494
This commit is contained in:
Daniel P. Berrange
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specs/juno/libvirt-driver-domain-metadata.rst
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specs/juno/libvirt-driver-domain-metadata.rst
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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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Libvirt driver domain metadata
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==============================
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https://blueprints.launchpad.net/nova/+spec/libvirt-driver-domain-metadata
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Metadata will be recorded in the libvirt domain XML configuration to provide
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information about the Nova instance that the domain corresponds to. The aim
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is to provide information that can be useful to administrators troubleshooting
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compute hosts.
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Problem description
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===================
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When troubleshooting a compute node there will be a number of running libvirt
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domains which correspond to Nova instances. There may also be other running
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domains which were not launched by Nova, for example, utility guests run by
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libguestfs for file injection. The libvirt domain uuid will match that of the
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Nova instance, but there is more information about a Nova instance that could
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usefully be provided to administrators. For example, the identity of the
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tenant who launched it, the original flavour name and/or settings, the time at
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which the domain was launched, and the version number of the Nova instance that
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launched it (can be relevant if Nova is upgraded while a VM is running).
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Proposed change
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===============
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The Libvirt domain XML configuration schema allows for applications to insert
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arbitrary metadata under a private XML namespace. The proposal is to make use
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of this to define some metadata that is relevant to Nova, specifically it will
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record
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- The nova package version
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- The display name of the instance (as matching 'nova list')
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- The name of the flavor
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- The creation time of the instance
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- The user and project ID/name of owner
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- The root disk glance image or cinder volume UUID
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This would correspond to the following XML blob
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::
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<domain type='kvm'>
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...rest of domain XML config...
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<metadata>
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<nova:instance xmlns:nova="http://openstack.org/nova/instance/1">
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<nova:package version="2014.2.3"/>
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<nova:flavor name="m1.small">
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<nova:memory>512</nova:memory>
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<nova:disk>10</nova:disk>
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....
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</nova:flavor>
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<nova:name>demo1vm</nova:name>
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<nova:creationTime>2014-12-25 12:03:20</nova:creationTime>
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<nova:owner>
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<nova:user uuid="85bd45c0...213684">joe</nova:user>
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<nova:project uuid="d33b8c0e...342d69">acmecorp</nova:project>
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</nova:owner>
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<nova:root type="image|volume" uuid="69f2991b...f29a8bc"/>
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</nova:instance>
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</metadata>
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</domain>
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Alternatives
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------------
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Administrators can ask libvirt for the UUID of the running instance and then
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attempt to trace all the information back via Nova APIs. If Nova itself is in
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some failure scenario though, this would not be possible. It also places more
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burden on the administrator to trace the info which could be provided directly
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in the Libvirt XML.
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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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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
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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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The compute host administrator will be able to ask libvirt to provide the XML
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config for the running instance and from there find out various useful pieces
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of metadata about the instance.
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Developer impact
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----------------
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None, this is entirely within the libvirt driver impl
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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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berrange
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Work Items
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----------
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* Extend the nova/virt/libvirt/config.py object model to represent the
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proposed metadata schema for Nova
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* Extend the nova/virt/libvirt/driver.py get_guest_config() method to fill
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in the metadata when generating guest XML config
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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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None required beyond unit tests
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Documentation Impact
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====================
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Document that the libvirt XML config contains this metadata as an aid
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for administrators debugging compute nodes.
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References
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==========
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* Libvirt XML format docs http://libvirt.org/formatdomain.html#elementsMetadata
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