On Fri, 6 Dec 2019, Alfredo Deza wrote: > On Fri, Dec 6, 2019 at 5:59 AM Sebastien Han <shan@xxxxxxxxxx> wrote: > > > > Hi, > > > > Following up on my previous ceph-volume email as promised. > > > > When running Ceph with Rook in Kubernetes in the Cloud (Aws, Azure, > > Google, whatever), the OSDs are backed by PVC (Cloud block storage) > > attached to virtual machines. > > This makes the storage portable if the VM dies, the device will be > > attached to a new virtual machine and the OSD will resume running. > > > > In Rook, we have 2 main deployments for the OSD: > > > > 1. Prepare the disk to become an OSD > > Prepare will run on the VM, attach the block device, run "ceph-volume > > prepare", then this gets complicated. After this, the device is > > supposed to be detached from the VM because the container terminated. > > However, the block is still held by LVM so the VG must be > > de-activated. Currently, we do this in Rook, but it would be nice to > > de-activate the VG once ceph-volume is done preparing the disk in a > > container. > > > > 2. Activate the OSD. > > Now, onto the new container, the device is attached again on the VM. > > At this point, more changes will be required in ceph-volume, > > particularly in the "activate" call. > > a. ceph-volume should activate the VG > > By VG you mean LVM's Volume Group? > > > b. ceph-volume should activate the device normally > > Not "normally" though right? That would imply starting the OSD which > you are indicating is not desired. > > > c. ceph-volume should run the ceph-osd process in foreground as well > > as accepting flag to that CLI, we could have something like: > > "ceph-volume lvm activate --no-systemd $STORE_FALG $OSD_ID $OSD_UUID > > <a bunch of flags>" > > Perhaps we need a new flag to indicate we want to run the osd > > process in foreground? > > Here is an example on how an OSD run today: > > > > ceph-osd --foreground --id 2 --fsid > > 9a531951-50f2-4d48-b012-0aef0febc301 --setuser ceph --setgroup ceph > > --crush-location=root=default host=minikube --default-log-to-file > > false --ms-learn-addr-from-peer=false > > > > --> we can have a bunch of flags or an ENV var with all the flags > > whatever you prefer. > > > > This wrapper should watch for signals too, it should reply to > > SIGTERM in the following way: > > - stop the OSD > > - de-activate the VG > > - exit 0 > > > > Just a side note, the VG must be de-activated when the container stops > > so that the block device can be detached from the VMs, otherwise, > > it'll still be held by LVM. > > I am worried that this goes beyond what I consider the scope of > ceph-volume which is: prepare device(s) to be part of an OSD. > > Catching signals, handling the OSD in the foreground, and accepting > (proxying) flags, sounds problematic for a robust implementation in > ceph-volume, even > if that means it will help Rook in this case. > > The other challenge I see is that it seems Ceph is in a transition > from being a baremetal project to a container one, except lots of > tooling (like ceph-volume) is deeply > tied to the non-containerized workflows. This makes it difficult (and > non-obvious!) in ceph-volume when adding more flags to do things that > help the containerized > deployment. > > To solve the issues you describe, I think you need either a separate > command-line tool that can invoke ceph-volume with the added features > you listed, or > if there is significant push to get more things in ceph-volume, a > separate sub-command, so that the `lvm` is isolated from the > conflicting logic. > > My preference would be a wrapper script, separate from the Ceph project. The end goal is to have this inside the ceph/daemon-base container. Making it part of ceph-volume is just one way to do that. Another wrapper script could accomplish the same thing (e.g., /usr/bin/ceph-osd-podwrapper). FWIW I like the idea of making it a subcommand that isn't tied to LVM specifically since it's basically sandwiching the OSD run with activate/deactive, and it could be made to work as/if/when the provisioning method evolves from lvm to something else over time. sage _______________________________________________ Dev mailing list -- dev@xxxxxxx To unsubscribe send an email to dev-leave@xxxxxxx
