f0b8204072
As discussed at our nova meetings, reorganize the juno specs into three directories: - proposed: things proposed which weren't approved - approved: things we approved but didn't implement - implemented: things approved and implemented The first I suspect is the most controversial. I've done this because I worry about the case where a future developer wants to pick up something dropped by a previous developer, but has trouble finding previous proposed specifications on the topic. Note that the actual proposed specs for Juno are adding in a later commit. Change-Id: Idcf55ca37a83d7098dcb7c2971240c4e8fd23dc8
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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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Quiescing filesystems with QEMU guest agent during image snapshotting
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=====================================================================
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https://blueprints.launchpad.net/nova/+spec/quiesced-image-snapshots-with-qemu-guest-agent
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When QEMU Guest Agent is installed in a kvm instance, we can request the
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instance to freeze filesystems via libvirt during snapshotting to make the
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snapshot consistent.
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Problem description
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===================
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Currently we need to quiesce filesystems (fsfreeze) manually before
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snapshotting an image of active instances to create consistent backups.
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This should be automated when QEMU Guest Agent is enabled.
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Proposed change
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===============
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When QEMU Guest Agent is enabled in an instance, Nova-compute libvirt driver
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will request the agent to freeze the filesystems (and applications if
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fsfreeze-hook is installed) before taking snapshot of the image.
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After taking snapshot, the driver will request the agent to thaw the
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filesystems.
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The prerequisites of this feature are:
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1. the hypervisor is 'qemu' or 'kvm'
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2. libvirt >= 1.2.5 (which has fsFreeze/fsThaw API) is installed in the
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hypervisor
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3. 'hw_qemu_guest_agent=yes' property in the image metadata is set to 'yes'
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and QEMU Guest Agent is installed and enabled in the instance
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When quiesce is failed even though these conditions are satisfied
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(e.g. the agent is not responding), snapshotting may fail by exception
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not to get inconsistent snapshots.
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Alternatives
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------------
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Rewrite nova's snapshotting with libvirt's domain.reateSnapshot API with
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VIR_DOMAIN_SNAPSHOT_CREATE_QUIESCE flag, although it will change the current
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naming scheme of disk images. In addition, it cannot be leveraged to implement
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live snapshot of cinder volumes.
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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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While taking snapshots, disk writes from the instance are blocked.
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Other deployer impact
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---------------------
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None
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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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tsekiyama
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Work Items
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----------
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Implement the automatic quiesce during snapshotting when it is available.
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Now the code is ready to review: https://review.openstack.org/#/c/72038/
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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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Live snapshotting with an image with qemu-guest-agent should be added to
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scenario tests.
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Note that it requires environment with libvirt >= 1.2.5.
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Documentation Impact
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====================
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Need to document how to use this feature in the operation guide (which
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currently recommends you use the fsfreze tool manually).
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References
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==========
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None
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