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
3.0 KiB
Quiescing filesystems with QEMU guest agent during image snapshotting
https://blueprints.launchpad.net/nova/+spec/quiesced-image-snapshots-with-qemu-guest-agent
When QEMU Guest Agent is installed in a kvm instance, we can request the instance to freeze filesystems via libvirt during snapshotting to make the snapshot consistent.
Problem description
Currently we need to quiesce filesystems (fsfreeze) manually before snapshotting an image of active instances to create consistent backups. This should be automated when QEMU Guest Agent is enabled.
Proposed change
When QEMU Guest Agent is enabled in an instance, Nova-compute libvirt driver will request the agent to freeze the filesystems (and applications if fsfreeze-hook is installed) before taking snapshot of the image. After taking snapshot, the driver will request the agent to thaw the filesystems.
The prerequisites of this feature are:
- the hypervisor is 'qemu' or 'kvm'
- libvirt >= 1.2.5 (which has fsFreeze/fsThaw API) is installed in the hypervisor
- 'hw_qemu_guest_agent=yes' property in the image metadata is set to 'yes' and QEMU Guest Agent is installed and enabled in the instance
When quiesce is failed even though these conditions are satisfied (e.g. the agent is not responding), snapshotting may fail by exception not to get inconsistent snapshots.
Alternatives
Rewrite nova's snapshotting with libvirt's domain.reateSnapshot API with VIR_DOMAIN_SNAPSHOT_CREATE_QUIESCE flag, although it will change the current naming scheme of disk images. In addition, it cannot be leveraged to implement live snapshot of cinder volumes.
Data model impact
None
REST API impact
None
Security impact
None
Notifications impact
None
Other end user impact
None
Performance Impact
While taking snapshots, disk writes from the instance are blocked.
Other deployer impact
None
Developer impact
None
Implementation
Assignee(s)
- Primary assignee:
-
tsekiyama
Work Items
Implement the automatic quiesce during snapshotting when it is available. Now the code is ready to review: https://review.openstack.org/#/c/72038/
Dependencies
None
Testing
Live snapshotting with an image with qemu-guest-agent should be added to scenario tests. Note that it requires environment with libvirt >= 1.2.5.
Documentation Impact
Need to document how to use this feature in the operation guide (which currently recommends you use the fsfreze tool manually).
References
None