Merge "Proposed blueprint for libvirt Sheepdog instances."
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specs/juno/libvirt-sheepdog-backed-instances.rst
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specs/juno/libvirt-sheepdog-backed-instances.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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Support Sheepdog ephemeral disks for libvirt driver
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====================================================
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https://blueprints.launchpad.net/nova/+spec/libvirt-sheepdog-backed-instances
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Add support for Sheepdog instance ephemeral disks.
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Problem description
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===================
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Sheepdog block devices can already be attached to QEMU and KVM
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virtual machines. Nova's libvirt driver supports most of the
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functionality. The only additional changes are to the image-backend
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drivers. Both Glance and Cinder support sheepdog backends, so this
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would complement the efforts made in those projects.
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Proposed change
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===============
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This change would extend several parts of the libvirt driver. In
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general, these changes are very similar to the changes required for
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the RBD driver. These changes would bring Sheepdog support into
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feature-parity with RBD, QEMU and other libvirt image drivers.
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- nova.virt.libvirt.driver would be extended with cleanup functions
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for Sheepdog, in the same way that ``cleanup_rbd_instance`` does
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for the RBD backend.
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- A new ``Image`` subclass class would be added to
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``nova.virt.libvirt.imagebackend`` for Sheepdog.
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- Helper functions would be added to ``nova.virt.libvirt.utils`` where needed.
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- /etc/nova/rootwrap.d/filters would be extended to support rootwrap
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on the ``dog`` command used to interact with Sheepdog.
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- See Deployer impact for configuration changes.
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Alternatives
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------------
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Cinder has existing support for Sheepdog volumes. One alternative
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is to use that driver and only launch instances from volumes. There
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are two problems with this option. First, it would not support
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instance disks that are deleted after the instance is destroyed.
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Second, for the end-user it requires additional steps to provision
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the volume before the instance is booted.
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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. This blueprint makes no REST API changes.
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Security impact
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---------------
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Rootwrap of 'dog' command on nova-compute machines.
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Notifications impact
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--------------------
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None. No plans for new notifications.
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Performance 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. This blueprint has no impact on python-novaclient or any other
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end-user interface.
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Other deployer impact
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---------------------
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To use this feature, a deployer must first set up a sheepdog cluster and
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then make several configuration changes to nova on machines running the
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nova-compute process. If Sheepdog is to be used with Glance and Cinder,
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the deployer must also make the appropriate configuration changes for those
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services.
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To setup a Sheepdog cluster, follow the install guide provided by
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Sheepdog [1]_. After setting up a Sheepdog cluster, each nova-compute
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process must be configured. The following options must be set under
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the ``[libvirt]`` section of ``nova.conf`` or ``nova-compute.conf``:
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- ``images_type=sheepdog`` This must be set to indicate that sheepdog should
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be used.
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- ``images_sheepdog_host=locahost`` Change this if the machine running the
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nova-compute process is not a member of the sheepdog cluster, or is not
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acting as a gateway node within the cluster.
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- ``images_sheepdog_port=7000``` Change this if the sheep process is listening
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on a different port than the default.
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For sites doing continuous deployment, this change will have no impact until
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the deployer changes the ``images_type`` setting to deliberately switch a
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nova-compute machine to use Sheepdog.
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There are no database migrations required for this change.
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Developer impact
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----------------
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This change would add an additional disk-backend to the libvirt driver,
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slightly increasing code support costs.
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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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<scott-devoid> Scott Devoid
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Other contributors:
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<None>
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Work Items
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----------
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- Implement basic support for Sheepdog images booted from a Glance image.
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- Implement snapshot support.
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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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Devstack integration is required before tempest can run functional
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tests against the Sheepdog drivers for Nova, Glance and Cinder. A patch
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has been proposed which would use Sheepdog for each service. [2]
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This, I think, would result in many functional tests of the Sheepdog
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drivers via the Tempest tests. However, a Jenkins job would need
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to be defined and VMs would need to be provisioned to run the jobs.
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It is not clear if openstack-infra is willing or capable of committing
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to a proliferation of CI test runs. There is a Juno Summit scheduled for
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this. [3]
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Documentation Impact
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====================
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- Configuration reference would need to be updated with the new configuration
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options. See the Deployer Impact section.
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- Cloud Administer or Operations guide should be updated with a section which
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describes in detail how to configure Sheepdog for nova and what sort of
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considerations should be taken into account, e.g. cluster size, Zookeeper vs
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Corosync, the use of gateway nodes.
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These documentation changes would happen as part of this blueprint.
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References
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==========
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.. [1] https://github.com/sheepdog/sheepdog/wiki
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.. [2] https://review.openstack.org/#/c/90244/
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.. [3] http://summit.openstack.org/cfp/details/198
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