On Tue, Nov 19, 2019 at 4:09 PM Florian Haas <flor...@citynetwork.eu> wrote: > > On 19/11/2019 21:32, Jason Dillaman wrote: > >> What, exactly, is the "reasonably configured hypervisor" here, in other > >> words, what is it that grabs and releases this lock? It's evidently not > >> Nova that does this, but is it libvirt, or Qemu/KVM, and if so, what > >> magic in there makes this happen, and what "reasonable configuration" > >> influences this? > > > > librbd and krbd perform this logic when the exclusive-lock feature is > > enabled. > > Right. So the "reasonable configuration" applies to the features they > enable when they *create* an image, rather than what they do to the > image at runtime. Is that fair to say?
The exclusive-lock ownership is enforced at image use (i.e. when the feature is a property of the image, not specifically just during the action of enabling the property) -- so this implies "what they do to the image at runtime" > > In this case, librbd sees that the previous lock owner is > > dead / missing, but before it can steal the lock (since librbd did not > > cleanly close the image), it needs to ensure it cannot come back from > > the dead to issue future writes against the RBD image by blacklisting > > it from the cluster. > > Thanks. I'm probably sounding dense here, sorry for that, but yes, this > makes perfect sense to me when I want to fence a whole node off — > however, how exactly does this work with VM recovery in place? How would librbd / krbd know under what situation a VM was being "recovered"? Should librbd be expected to integrate w/ IPMI devices where the VM is being run or w/ Zabbix alert monitoring to know that this was a power failure so don't expect that the lock owner will come back up? The safe and generic thing for librbd / krbd to do in this situation is to just blacklist the old lock owner to ensure it cannot talk to the cluster. Obviously in the case of a physically failed node, that won't ever happen -- but I think we can all agree this is the sane recovery path that covers all bases. > From further upthread: > > > Semi-relatedly, as I understand it OSD blacklisting happens based either > > on an IP address, or on a socket address (IP:port). While this comes in > > handy in host evacuation, it doesn't in in-place recovery (see question > > 4 in my original message). > > > > - If the blacklist happens based on IP address alone (and that's what > > seems to be what the client attempts to be doing, based on our log > > messages), then it would break recovery-in-place after a hard reboot > > altogether. > > > > - Even if the client would blacklist based on an address:port pair, it > > would be just very unlikely that an RBD client used the same source port > > to connect after the node recovers in place, but not impossible. > > Clearly though, if people set their permissions correctly then this > blacklisting seems to work fine even for recovery-in-place, so no reason > for me to doubt that, I'd just really like to understand the mechanics. :) Yup, with the correct permissions librbd / rbd will be able to blacklist the lock owner, break the old lock, and acquire the lock themselves for R/W operations -- and the operator would not need to intervene. > Thanks again! > > Cheers, > Florian > -- Jason _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
