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Thank you for your reply


I see that hw_qemu_guest_agent can freeze and unfreeze the guest os file system when creating snapshots, but I do not know the meaning of freezing and unfreezing the file system. In other words, if the qemu guest agent is not specified, the guest os cannot be frozen or unfrozen. What are the differences between freezing and thawing operations? How applicable it is in the cloud scenario.





------------------ 原始邮件 ------------------
发件人:                                                                                                                        "Sean Mooney"                                                                                    <smooney at redhat.com>;
发送时间: 2023年4月20日(星期四) 晚上7:00
收件人: "啧啧啧"<1148203170 at qq.com>;"openstack-discuss"<openstack-discuss at lists.openstack.org>;

主题: Re: [nova]qemu-guest-agent Used in openstack



The hw_qemu_guest_agent image property is used to enable the qemu channel (basically a unix socket) use to enabel comunciation
between a "qemu guest agent" there is a default qemu one but other cloud vendor have created there own. i know ovh has one they
maintain for there cloud. the upstream qemu guest agent is not used for monitoring. i belive it can be used to monitor the guest if
you write a custom one but that is not somethign that is directly supported by upstream openstack.

nova only uses it for one thing.
we supprot the generic qemu geusts agent ablity to freeze the guest file system and unfreeze it to take
snapshots without any inflight data writes.

prometheus is not really integrated with openstack at least not in a way that is maintained/supported by
the openstack comunity as an officall project as far as i am aware.
i do not belive there is any interaction between prometheus and the qemu guest agent although there is a libvirt exporter
for prometious so perhaps it has support for interafcting with the qemu agent in some way.

form a nova point of view we just enable the qemu guest agent to fucntion if you have installed it in your guest but we
dont really try to use it to monitor or manage the guest in general beyond the orginal uscase for consitent snapshots.
hopefully that helps.


On Thu, 2023-04-20 at 18:13 +0800, 啧啧啧 wrote:
> Hi,
> 
> 
> We discovered the use of qemu-guest-agent in openstack,Set hw_qemu_guest_agent=yes to the metadata parameter on the image.
> https://docs.openstack.org/mitaka/config-reference/compute/hypervisor-kvm.html
> 
> 
> Meanwhile, the application of qemu-guest-agent in cloud scenarios is investigated. It is found that Qemu-guest-Agent can be used for guest os performance monitoring, snapshot backup, and guest OS-level failover.
> But these things can be done in openstack with prometheus and&nbsp; instance backup,There may be some differences between them.
> 
> 
> Sorry, I am not familiar with how hw_qemu_guest_agent is used in openstack, and I do not know the operations that can be performed on guest os in openstack by configuring hw_qemu_guest_agent.
> Only through qemu official know some of the effects.I want to clarify the use of hw_qemu_guest_agent. Other components of openstack, such as the prometheus service, can be used instead.
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