10:58 a.m.
On Wed, 2012-02-22 at 17:33 +0200, Doron Fediuck wrote:
Another concern raised is swap and overcommit. First version would
likely disable swap completely. This would disable overcommit as well.
Future versions could enable a local disk to be used completely for
swap, but that is another tradeoff that people would need to evaluate
when choosing between stateless and stateful installs.
Mike
On 22/02/12 16:57, Mike Burns wrote:
> There has been a lot of interest in being able to run stateless Nodes
> with ovirt-engine. ovirt-node has designed a way [1] to achieve this on
> the node side, but we need input from the engine and vdsm teams to see
> if we're missing some requirement or if there needs to be changes on the
> engine/vdsm side to achieve this.
> As it currently stands, every time you reboot an
ovirt-node that is
> stateless, it would require manually removing the host in engine, then
> re-registering/approving it again in engine.
> Any thoughts, concerns, input on how to solve this?
> Thanks
> Mike
> [1] http://ovirt.org/wiki/Node_Stateless
Some points need to be considered;
- Installation issues
* Just stating the obvious, which is users need
to remove-add the host on every reboot. This will
not make this feature a lovable one from user's point of view.
Yes, this is something that will cause this to be a non-starter. We'd
need to change something in the engine/vdsm to make it smoother.
Perhaps, a flag in engine on the host saying that it's stateless. Then
if a host comes up with the same information, but no certs, etc, it
would validate some other embedded key (TPM, key embedded in the node
itself), and auto-approve it to be the same state as the previous boot
* During initial boot, vdsm-reg configures the networking
and creates a management network bridge. This is a very
delicate process which may fail due to networking issues
such as resolution, routing, etc. So re-doing this on
every boot increases the chances of loosing a node due
to network problems.
vdsm-reg runs on *every* boot anyway and renames the bridge. This is
something that was debated previously, but it was decided to re-run it
every boot.
* CA pollution; generating a certificate on each reboot
for each node will create a huge number of certificates
in the engine side, which eventually may damage the CA.
(Unsure if there's a limitation to certificates number,
but having hundreds of junk cert's can't be good).
We could have vdsm/engine store the certs on the engine side, and on
boot, after validating the host (however that is done), it will load the
certs onto the node machine.
* Today there's a supported flow that for nodes with
password, the user is allowed to use the "add host"
scenario. For stateless, it means re-configuring a password
on every boot...
Stateless is really targeted for a PXE environment. There is a
supported kernel param that can be set that will set this password.
Also, if we follow the design mentioned ^^, then it's not an issue since
the host will auto-approve itself when it connects
- Other issues
* Local storage; so far we were able to define a local
storage in ovirt node. Stateless will block this ability.
Yes, this would be unavailable if you're running stateless. I think
that's a fine tradeoff since people want the host to be diskless.
* Node upgrade; currently it's possible to upgrade a node
from the engine. In stateless it will error, since no where
to d/l the iso file to.
Upgrade is handled easily by rebooting the host after updating the pxe
server
* Collecting information; core dumps and logging may not
be available due to lack of space? Or will it cause kernel
panic if all space is consumed?
A valid concern, but a stateless environment would likely have
collectd/rsyslog/netconsole servers running elsewhere that will collect
the logs. kdumps can be configured to dump remotely as well.