| Posted | Nick | Remark | |
|---|---|---|---|
| #openstack-nova - 2023-02-21 | |||
| 18:58:45 | sean-k-mooney | not a schduler bug | |
| 18:59:01 | sean-k-mooney | it will fail in pre-live-migrate | |
| 18:59:16 | sean-k-mooney | and the vm will stay in active on the host | |
| 18:59:21 | sean-k-mooney | (source host) | |
| 18:59:51 | mnaser | now if you’re using rbd for images_type and you have 2 clusters with each az using different cluster | |
| 18:59:51 | mnaser | now if you’re using rbd for images_type and you have 2 clusters with each az using different cluster | |
| 19:00:23 | mnaser | And you do a live migrate and end up with vm running on the other side and but using it’s original storage | |
| 19:00:23 | mnaser | And you do a live migrate and end up with vm running on the other side and but using it’s original storage | |
| 19:00:27 | sean-k-mooney | then you need to configure your filters to ensure that you target the vsm to spcific cluster using a flavor or simialr | |
| 19:00:45 | mnaser | And then on resize ops it blows up horribly because it’s trying to use the destination cluster id | |
| 19:00:45 | mnaser | And then on resize ops it blows up horribly because it’s trying to use the destination cluster id | |
| 19:01:11 | sean-k-mooney | yep that operator error if they did not configure things properly to prevent this | |
| 19:01:37 | sean-k-mooney | adressing theses usecase is somethign that could be done but it would be a feature not a bug | |
| 19:01:37 | mnaser | How? So if you have 3 azs you create 3 flavors? | |
| 19:01:43 | sean-k-mooney | yep | |
| 19:01:53 | mnaser | Do you think that’s user friendly at all | |
| 19:01:53 | mnaser | Do you think that’s user friendly at all | |
| 19:02:13 | sean-k-mooney | nope but its how its currently desigined | |
| 19:02:23 | sean-k-mooney | and fixing it would not eb a bug fix | |
| 19:02:41 | mnaser | So really what you’re saying is nova will do live migrations that will break your vm | |
| 19:02:41 | mnaser | So really what you’re saying is nova will do live migrations that will break your vm | |
| 19:02:45 | mnaser | And that’s not a bug | |
| 19:02:45 | mnaser | And that’s not a bug | |
| 19:02:58 | sean-k-mooney | nope | |
| 19:03:19 | sean-k-mooney | nova check if it can attach the volcumes to the select host before it live migrates | |
| 19:03:27 | sean-k-mooney | so it will pass the schduler but fail in pre live migrate | |
| 19:03:33 | mnaser | ok, lets put that aside and talk about the users who use images_type=rbd | |
| 19:03:36 | mnaser | with different az's | |
| 19:03:44 | mnaser | it will break thoes vms | |
| 19:03:45 | sean-k-mooney | also live migrate is an admin only api and we allow you as an admin to select the host | |
| 19:04:06 | mnaser | ok when we're deploying openstack for customers they don't expect to sit and decide which host they are going to move things into at scale | |
| 19:04:15 | sean-k-mooney | mnaser: not if you use cross_az_atch=false | |
| 19:04:27 | mnaser | if i tell them 'sorry, openstack is kinda silly, it picks the wrong hosts, you just pick the right host yourself instead' | |
| 19:04:53 | mnaser | non-bfv, images_type=rbd, 2 az's with ceph cluster each will result in broken live migrations | |
| 19:04:54 | sean-k-mooney | if you want to propsoe a new feature for this im open to review that | |
| 19:05:16 | sean-k-mooney | what i do not think woudl be corerct it considerign this a bug when we previously declared it out of scope and backproting this | |
| 19:05:53 | sean-k-mooney | mnaser: it would break if the ceph cluster was inaccable yes | |
| 19:06:09 | sean-k-mooney | although i belvie | |
| 19:06:20 | sean-k-mooney | the vm would stay runnign on the souce host in active | |
| 19:06:24 | sean-k-mooney | with the migration in error | |
| 19:06:30 | mnaser | and any reasonable operator would make a sane assumption that the cloud would not live migrate across az's | |
| 19:06:42 | sean-k-mooney | libvirt will detect teh qemu instance was not able to connect | |
| 19:06:44 | mnaser | the vm does migrate if the cluster is accessible, and then all further operations like resize/migrate/etc are broken | |
| 19:06:47 | sean-k-mooney | and it shoudl abort the migration | |
| 19:06:57 | mnaser | so it goes into a user-facing broken state | |
| 19:07:05 | sean-k-mooney | az are not fault domain | |
| 19:07:12 | sean-k-mooney | or isolated segments | |
| 19:07:36 | sean-k-mooney | mnaser: i do not belive you will get into a user facing broken state for live migration | |
| 19:07:58 | mnaser | you will.. if both ceph clusters are accessible, then the further operations will try to use the fsid of the target vm | |
| 19:08:12 | mnaser | i can ask to get tracebacks and logs from teh customer | |
| 19:08:39 | mnaser | but it makes sense since now its trying to use the _new_ cluster fsid, but doesnt find the volume, since its attached from the old cluster fsid | |
| 19:08:43 | sean-k-mooney | if both are accsabel and you only have ceph cred for one of them on the compute host then qemu will not be able to conenct | |
| 19:09:24 | sean-k-mooney | mnaser: that sound like they are trying to use the same user/keyring between both clusters | |
| 19:09:29 | mnaser | ok, assume one cluster with different pools when you're using ceph then | |
| 19:09:31 | sean-k-mooney | which is incorect | |
| 19:09:33 | mnaser | i havent dug that deep into their stuff | |
| 19:10:03 | mnaser | now when nova tries to do things it'll do it on the new pool but cant find that _disk image | |
| 19:10:44 | sean-k-mooney | which will fail when we try to create the qemu instance on the dest | |
| 19:10:49 | sean-k-mooney | but the migraiton shoudl abort then | |
| 19:11:03 | mnaser | isnt the old xml get transferred | |
| 19:11:05 | sean-k-mooney | and the vm shoudl stay runing on the souce node in actie | |
| 19:11:06 | mnaser | so it successfully completes? | |
| 19:11:16 | mnaser | s/isnt/doesnt/ | |
| 19:11:23 | sean-k-mooney | no the vm get created really really early on the dest | |
| 19:11:34 | mnaser | i dont think we rebuild xml from scratch on target but rather rely on shipping the xml from the old libvirt to the new one? | |
| 19:11:36 | sean-k-mooney | we have to create the vm on the dest so that the ram can be copied | |
| 19:11:54 | sean-k-mooney | mnaser: we generate a new xml on the souce for the dest | |
| 19:12:03 | mnaser | ok something is not adding up then | |
| 19:12:08 | sean-k-mooney | so my expectation is that it shoudl use the old cluster | |
| 19:12:19 | sean-k-mooney | so you woudl have cross az traffic | |
| 19:12:22 | mnaser | oh ok right yes, it would add up nevermind | |
| 19:12:29 | mnaser | if we generate xml on source for the dest it'll have the old | |
| 19:12:30 | sean-k-mooney | what might break is a hard reboot after that | |
| 19:12:38 | mnaser | yes exactly, or resize, etc | |
| 19:13:00 | sean-k-mooney | right but thats a complete differnt issue | |
| 19:13:13 | sean-k-mooney | we do not supprot move operations across diffent stroagge backends at all | |
| 19:13:30 | sean-k-mooney | and preventing that is left to the operator today and it has alyas been that way in nova | |
| 19:13:52 | mnaser | so as someone whos trying to get people to use openstack, giving them a big gun to shoot themselves in the foot | |
| 19:14:12 | mnaser | and then when they do that because it doesnt seem very trivial and obvious that what they did is wrong | |
| 19:14:18 | sean-k-mooney | mnaser: the simpelr approch si to use cells | |
| 19:14:20 | mnaser | when they went ahead, created az, aggregates, etc | |
| 19:14:36 | sean-k-mooney | we do not allwo cross cell live migration | |
| 19:14:37 | mnaser | that's a really good point | |
| 19:14:57 | mnaser | so ensure same storage backend inside a cell | |
| 19:15:03 | mnaser | seems like pretty sane advice | |
| 19:15:04 | sean-k-mooney | yes | |
| 19:15:16 | sean-k-mooney | with all that said we coudl work on a feature to adress this | |
| 19:15:45 | sean-k-mooney | but it would be a new feature and it would have to still allow usecase wehre cross az move operations make sense | |
| 19:16:14 | sean-k-mooney | mnaser: for example we recently added a similar feature for neutron routed networks | |
| 19:16:47 | sean-k-mooney | https://specs.openstack.org/openstack/nova-specs/specs/wallaby/implemented/routed-networks-scheduling.html | |
| 19:16:51 | mnaser | sometimes i really feel letting users create az's was a massive mistake lol | |
| 19:17:02 | sean-k-mooney | well users cant | |
| 19:17:04 | mnaser | it was always so loose and there's so many people who get shot in the foot with it | |
| 19:17:08 | mnaser | nah i mean from an operator perspective | |
| 19:17:11 | sean-k-mooney | its admin only unless you change the policy | |
| 19:17:26 | mnaser | people build out something and then it almost never gives them what they want | |
| 19:17:29 | sean-k-mooney | oh well the issue is peopel consufe nova az with aws | |
| 19:17:35 | sean-k-mooney | and they are nothign like each other | |
| 19:17:55 | mnaser | yeah | |
| 19:18:04 | sean-k-mooney | so before wallaybe tehre was no schduler supprot for route l3 networks | |