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#openstack-nova - 2021-07-13
16:31:30 gibi but I have one note
16:31:47 gibi I sent out a doodle about the coming PTG
16:32:00 sean-k-mooney ah i was going to ask about that i saw the ooo one
16:32:15 gibi #link http://lists.openstack.org/pipermail/openstack-discuss/2021-July/023560.html
16:32:35 gibi in the ML thread I have a question about the amount of slots we would need
16:32:54 gibi and also we have brand new PTG etherpad too https://etherpad.opendev.org/p/nova-yoga-ptg
16:33:21 sean-k-mooney i do think that 4 days with 4 hour slot is likely better yes
16:33:40 sean-k-mooney if it was in person we likely owuld do 3 8 hour slots - breaks
16:35:07 gibi yeah my experience tells me we could use more time than 3x4 hours
16:35:18 sean-k-mooney when do you need to inform the organisers
16:35:36 gibi 21st of July
16:35:41 gibi so next week
16:35:42 sean-k-mooney ack
16:35:53 gibi but I think I can always add more slots then remove it later
16:36:08 sean-k-mooney yep
16:36:20 gibi any other topic for today?
16:36:23 alistarle Hello guys, concerning this blueprint https://review.opendev.org/c/openstack/nova/+/794837, do you have any question about it, and what is the next step ?
16:37:21 sean-k-mooney looks liek lee has a -1
16:37:32 sean-k-mooney has this been disucsed as a specless blueprint in the past
16:38:13 alistarle Yep, but I already answer in previous comment I think, but I can sum up for lee I for sure
16:38:30 lyarwood alistarle: yeah sorry did I miss the justification for this?
16:38:44 alistarle What do you mean about a speechless blueprint ? Because yes, there is a blueprint for that: https://blueprints.launchpad.net/nova/+spec/configure-direct-snapshot
16:38:47 lyarwood alistarle: I couldn't work out how you would be able to do this without manually flattening disks
16:39:09 gibi sean-k-mooney: I think this is the time alistarle asks for the approval of the specless bp
16:39:43 sean-k-mooney alistarle: that is a blueprint not a spec. a spec is a serate document that describe the usecase in detial and the design
16:39:45 sean-k-mooney gibi: ack
16:40:01 sean-k-mooney alistarle: can you summerise what you want to enable
16:40:50 alistarle Sure, I want to make the direct snapshot feature configurable, because for now, nova will not honor the glance configuration when creating a snapshot, but trying to guess it from the actual nova backend
16:41:18 dansmith what does that mean? "not honor the glance configuration" ?
16:42:10 sean-k-mooney alistarle: is this a glance multistore envoinment? or a case where glance does not use ceph for storage?
16:42:22 alistarle Let's say you 1. Store your image on ceph, and use copy on write to create VM, so you are storing your VM disk as images child in RBD, but during life of your cloud you want to move out from ceph. So 2. You remove your rbd backend from glance and put a swift one instead
16:43:21 alistarle With this configuration, nova will never call glance to check which backend is enabled, and he will always store the snapshot in ceph, even if it is not a declared glance backend
16:43:21 sean-k-mooney alistarle: are we talking about cinder volumes for the vm or the rbd image backend?
16:43:29 sean-k-mooney in nova.conf
16:43:32 lyarwood sean-k-mooney: rbd image backend
16:44:01 alistarle It it for a case when you used RBD as a glance store, then you replace it with a swift one, and you want to progressively move out from ceph
16:44:10 sean-k-mooney so the request is to flaten the snapshots effectivly in ceph and then have new shapshots go to swift
16:44:18 dansmith alistarle: okay I thought I asked you this question on the spec
16:44:41 sean-k-mooney alistarle: well one thing we do not support is changing the nova image_types backend
16:45:01 sean-k-mooney including via a move operation like cold migrate
16:45:04 lyarwood sean-k-mooney: you wouldn't, that doesn't control where the image is
16:45:05 dansmith alistarle: maybe what you want is to be able to tell nova-compute which glance backend you want to snapshot to, to create a flattened snapshot in the desired store, which may not be the rbd one?
16:45:31 sean-k-mooney lyarwood: well im aware of that but the usecase given was removing ceph
16:45:36 alistarle I think it is a good catch dansmith
16:45:38 dansmith telling it not to use rbd snapshotting "just because" is more confusing
16:45:42 lyarwood dansmith: does Glance support moving images between backends?
16:45:56 dansmith lyarwood: copying, yes, but that's not what I mean
16:46:00 lyarwood sean-k-mooney: dropping rbd just for Glance AFAICT
16:46:14 sean-k-mooney alistarle: is ^ the case
16:46:26 dansmith lyarwood: I meant tell nova "specifically create a flattened snapshot and upload it to a specific glance backend"
16:46:45 sean-k-mooney dansmith: that i think would be useful in other cases too
16:47:00 dansmith lyarwood: I don't think glance really exposes parent-child relationships anyway, so you couldn't expect to copy/move a hierarchy between backends
16:47:01 sean-k-mooney adding a glance store parater to the snapshot api i think woudl be resonable
16:47:03 dansmith either way,
16:47:14 dansmith I think it's quite clear that this can't be a specless bp :)
16:47:14 alistarle So you think it is better to change the snapshot API to allow users to choose which glance backend to use to snap the image ?
16:47:35 alistarle Yeah I see you point, for sure it will require a spec in that case
16:47:46 dansmith alistarle: that's not what I was suggesting, although that might also be an option.. the problem is, many ops will *not* want users to choose the pathologically terrible option, which you seem to want :)
16:48:10 alistarle But actually we will need to do the same code, so if a user explicitly specify a glance store, we need to bypass the direct_snapshot process
16:48:11 dansmith I was suggesting a conf option for nova-compute to tell it "always snapshot to glance backend X" or something
16:48:34 dansmith instead of letting a user choose
16:48:54 alistarle Because as of now, rbd image_backend do not care about glance config, he will magically decide to use ceph because VM disk is stored in ceph
16:49:08 sean-k-mooney i kind of dislike doing this per host but i guess a host level config might be useful for an edge deployment
16:49:55 sean-k-mooney alistarle: correct although that is partly be desgin
16:50:01 alistarle Oh I see, so instead of putting a config option to "disable direct snapshot", we put an option to "choose a glance backend"
16:50:27 alistarle And if we specify this option, we skip the direct_snapshot to always call glance
16:50:37 sean-k-mooney alistarle: well not nessisarly
16:50:48 sean-k-mooney if the specifed backedn was ceph
16:51:03 dansmith sean-k-mooney: letting users choose the backend on snapshot will mean they try all kinds of things that won't work or are terrible for performance
16:51:03 sean-k-mooney then direct would stil make sense
16:51:06 sean-k-mooney if the vm was backed by that ceph cluster
16:51:14 dansmith sean-k-mooney: like a user who is currently on ceph always choosing the file backend, causing us to always flatten and upload when we shouldn't be
16:51:43 sean-k-mooney dansmith: yes although i was wondiering if people woudl want to do that for data reducnace reasons
16:52:17 sean-k-mooney e.g. normally backup to local edge site with a snapshot and ocationally do it to central site
16:52:31 dansmith sean-k-mooney: I mean, it would be nice, but I think we'd need policy, defaults, and some sort of way to know which ones the compute can even talk to
16:52:48 dansmith sean-k-mooney: yeah, but not backup from one edge site to another.. that would be terribad
16:52:58 dansmith so we'd have to have some mapping of who can do what, etc
16:53:13 sean-k-mooney ya which is not realy somethng a normal user woudl be aware off
16:53:20 dansmith for sure
16:53:34 sean-k-mooney so we have 2 pothtial host level cofnig options
16:53:49 sean-k-mooney disableing direct snapshto whihc to me feels more like a workaround option
16:53:58 sean-k-mooney and dansmith's glance backend option
16:54:13 sean-k-mooney *glance store
16:54:43 dansmith yup.. the former is a workaround for sure, and as we've noted here, hard to even grok what or why you'd want it,
16:54:52 sean-k-mooney im a little concerned the host level glance store option will have implications for shelve and cross cell migration
16:55:08 dansmith but the latter is at least useful for migrating in or out of some thing, or directing snapshots to an appropriate on- or off-site location depending
16:55:32 dansmith sean-k-mooney: well, whatever the default is today already does, AFAIK
16:55:51 sean-k-mooney i do think i prefer the store approch
16:56:06 sean-k-mooney ya fair we just assume that glance is accable everywhere
16:56:17 gibi we have 5 minutes left, is there any other topic today? if not the we can continue this of course
16:56:27 dansmith spec on this for sure tho
16:56:49 gibi the spec it is
16:56:53 gibi then
16:57:07 gibi alistarle: please note that we have spec freeze on Thursday for Xena
16:57:32 lyarwood Quick one from me, I'm out for the next ~2 or so weeks, stephenfin is babysitting some stuff while I'm gone.
16:57:48 gibi lyarwood: thanks for the headsup
16:58:27 gibi if nothing else for today, then I will close the meeting but you can continue discussing the snapshot issue
16:59:18 gibi than thanks for joining
16:59:21 opendevmeet Minutes: https://meetings.opendev.org/meetings/nova/2021/nova.2021-07-13-16.00.html
16:59:21 opendevmeet Minutes (text): https://meetings.opendev.org/meetings/nova/2021/nova.2021-07-13-16.00.txt

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