Libvirt driver domain metadata

Libvirt driver domain metadata

https://blueprints.launchpad.net/nova/+spec/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.

Problem description

When troubleshooting a compute node there will be a number of running libvirt domains which correspond to Nova instances. There may also be other running domains which were not launched by Nova, for example, utility guests run by libguestfs for file injection. The libvirt domain uuid will match that of the Nova instance, but there is more information about a Nova instance that could usefully be provided to administrators. For example, the identity of the tenant who launched it, the original flavor name and/or settings, the time at which the domain was launched, and the version number of the Nova instance that launched it (can be relevant if Nova is upgraded while a VM is running).

Proposed change

The Libvirt domain XML configuration schema allows for applications to insert arbitrary metadata under a private XML namespace. The proposal is to make use of this to define some metadata that is relevant to Nova, specifically it will record

  • The nova package version

  • The display name of the instance (as matching ‘nova list’)

  • The name of the flavor

  • The creation time of the instance

  • The user and project ID/name of owner

  • The root disk glance image or cinder volume UUID

This would correspond to the following XML blob

<domain type='kvm'>
  ...rest of domain XML config...
  <metadata>
    <nova:instance xmlns:nova="http://openstack.org/nova/instance/1">
      <nova:package version="2014.2.3"/>
      <nova:flavor name="m1.small">
        <nova:memory>512</nova:memory>
        <nova:disk>10</nova:disk>
        ....
      </nova:flavor>
      <nova:name>demo1vm</nova:name>
      <nova:creationTime>2014-12-25 12:03:20</nova:creationTime>
      <nova:owner>
        <nova:user uuid="85bd45c0...213684">joe</nova:user>
        <nova:project uuid="d33b8c0e...342d69">acmecorp</nova:project>
      </nova:owner>
      <nova:root type="image|volume" uuid="69f2991b...f29a8bc"/>
    </nova:instance>
  </metadata>
</domain>

Alternatives

Administrators can ask libvirt for the UUID of the running instance and then attempt to trace all the information back via Nova APIs. If Nova itself is in some failure scenario though, this would not be possible. It also places more burden on the administrator to trace the info which could be provided directly in the Libvirt XML.

Data model impact

None

REST API impact

None

Security impact

None

Notifications impact

None

Other end user impact

None

Performance Impact

None

Other deployer impact

The compute host administrator will be able to ask libvirt to provide the XML config for the running instance and from there find out various useful pieces of metadata about the instance.

Developer impact

None, this is entirely within the libvirt driver impl

Implementation

Assignee(s)

Primary assignee:

berrange

Work Items

  • Extend the nova/virt/libvirt/config.py object model to represent the proposed metadata schema for Nova

  • Extend the nova/virt/libvirt/driver.py get_guest_config() method to fill in the metadata when generating guest XML config

Dependencies

None

Testing

None required beyond unit tests

Documentation Impact

Document that the libvirt XML config contains this metadata as an aid for administrators debugging compute nodes.

References

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nova-specs