Hi,
I've started working on a saner way to deploy OSD with Rook so that
they don't use the rook binary image.
Why were/are we using the rook binary to activate the OSD?
A bit of background on containers first, when executing a container,
we need to provide a command entrypoint that will act as PID 1. So if
you want to do pre/post action before running the process you need to
use a wrapper. In Rook, that's the rook binary, which has a CLI and
can then "activate" an OSD.
Currently, this "rook osd activate" call does the following:
* sed the lvm.conf
* run c-v lvm activate
* run the osd process
On shutdown, we intercept the signal, "kill -9" the osd and de-activate the LV.
I have a patch here:
https://github.com/rook/rook/pull/4386, that
solves the initial bullet points but one thing we cannot do is the
signal catching and the lv de-activation.
Before you ask, Kubernetes has pre/post-hook but they are not
reliable, it's known and documented that there is no guarantee they
would actually run before or after the container starts/stops. We
tried and we had issues.
Why do we want to stop using the rook binary for activation? Because
each time we get a new binary version (new operator version), this
will restart all the OSDs, even if the deployment spec didn't change,
at least if nothing else than the rook image version changed.
Also with containers, we have seen so many issues working with LVM,
just to name a few:
* adapt lvm filters
* interactions with udev - need to tune the lvm config, even c-v
itself has lvm flag to not sync with udev built-in
* several bindmounts
* lvm package must be present on the host even if running in containers
* SELinux, yes lvm calls SELinux commands under the hood and pollute
the logs in some scenarios
Currently, one of the ways I can see this working is by not using LVM
when bootstrapping OSDs. Unfortunately, some of the logic cannot go in
the OSD code since the lv de-activation happens after the OSD stops.
We need to de-activate the LV so when running in the Cloud the block
can safely be re-attached to a new machine without LVM issues.
I know this will be a bit challenging and might ultimately look like
ceph-disk but it'd be nice to consider it.
What about a small prototype for Bluestore with block/db/wal on the same disk?
If this gets rejected, I might try a prototype for not using c-v in
Rook or something else that might come up with this discussion.
Thanks!
S้bastien Han
Senior Principal Software Engineer, Storage Architect
"Always give 100%. Unless you're giving blood."
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