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2017-12-07 10:27 GMT+08:00 Mathieu Gagné <mgagne at calavera.ca>:
> On Wed, Dec 6, 2017 at 9:13 PM, Jaze Lee <jazeltq at gmail.com> wrote:
>> 2017-12-07 7:12 GMT+08:00 Matt Riedemann <mriedemos at gmail.com>:
>>> On 12/6/2017 2:11 AM, 李杰 wrote:
>>>>
>>>> Hi,all
>>>>
>>>>         Now the boot from volume 's instance of rebuild operation has a
>>>> problem.For example,after the rebuild operation,the instance 's root disk is
>>>> not replace.
>>>> I found the reason is that when we use the "_build_resources" function to
>>>> prepare source,it obtains the block devices according to the previous
>>>> instance 's uuid and attaches them to instance.So boot from volume 's
>>>> instance of rebuild operation doesn't update data.
>>>>         To solve it,I plan to use CLI 's "metadata" option,to increase a
>>>> key name "source_type".The "source_type" includes "snapshot" and "image".We
>>>> can judge from "source_type".If the "source_type" is "snapshot",we can
>>>> transform the given snapshot to a volume and attach this volume to
>>>> instance.If the "source_type" is "image",we don't handle it.
>>>>         Can you give me some advice?Help in troubleshooting this issue
>>>> will be appreciated.
>>>>
>>>
>>> See: https://review.openstack.org/#/c/520660/
>>>
>>> We just started disallowing rebuilding a volume-backed instance where the
>>> image changes during the rebuild. We don't support it in the compute
>>> service, as you've found out, so we're going to make it a fast failure in
>>> the API.
>>
>> Well, are there some reasons for you want to disallowing rebuilding a
>> volume-backend instance.
>> Just give the the review is not a convincing answer.
>>
>
> Rebuilding a volume-backed instance never worked. While the API
> currently accepts your request, nothing will happen. The instance
> won't be rebuilt as expected.
>
> There had been a couple of proposals/changes to add support:
> * https://review.openstack.org/#/c/442295/
> * https://review.openstack.org/#/c/305079/
>
> But technical challenges have been uncovered, making it harder to
> implement a proper solution.
>
> The change [1] linked by Matt Riedemann proposes failing rapidly so
> the user isn't under the false impression that a rebuild is being
> performed when in fact, nothing will happen.
>
> I do agree that being able to rebuild a volume-backed instance would
> be a great addition. We have been offering volume-backed instance for
> more than 4 years and our users love it.
> But for now, rebuild just doesn't work at all. It's better to send the
> right message through the API by failing fast.
>
> [1] https://review.openstack.org/#/c/520660/

Oh, I think it is not a proper solution. Adding a fast failure is much easier
than to support rebuilding of volume-backend instance.
I found the last reason to abandon the review at
https://review.openstack.org/#/c/305079/
is because the design is not very clear and lack of bp.
So everyone who wants to add this feature to nova is welcome. Please go ahead.




>
> --
> Mathieu
>
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谦谦君子