[ClusterLabs] Informing RAs about recovery: failed resource recovery, or any start-stop cycle?

Andrew Beekhof abeekhof at redhat.com
Thu Jun 23 19:22:48 EDT 2016

On Fri, Jun 24, 2016 at 1:26 AM, Adam Spiers <aspiers at suse.com> wrote:
> Adam Spiers <aspiers at suse.com> wrote:
>> As per the FIXME, one remaining problem is dealing with this kind of
>> scenario:
>>   - Cloud operator notices SMART warnings on the compute node
>>     which is not yet causing hard failures but signifies that the
>>     hard disk might die soon.
>>   - Operator manually runs "nova service-disable" with the intention
>>     of doing some maintenance soon, i.e. live-migrating instances away
>>     and replacing the dying hard disk.
>>   - Before the operator gracefully shuts down nova-compute, an I/O
>>     error from the disk causes nova-compute to fail.
>>   - Pacemaker invokes the monitor action which spots the failure.
>>   - Pacemaker invokes the stop action which runs service-disable.
>>   - Pacemaker attempts to restart nova-compute by invoking the start
>>     action.  Since the disk failure is currently intermittent, we
>>     get (un)lucky and nova-compute starts fine.
>>     Then it calls service-enable - BAD!  This is now overriding the
>>     cloud operator's manual request for the service to be disabled.
>>     If we're really unlucky, nova-scheduler will now start up new VMs
>>     on the node, even though the hard disk is dying.
>> However I can't see a way to defend against this :-/
> OK, I think I figured this out.  The answer is not to use
> service-disable at all, but to use force_down in the same way we
> already use it during fencing.  This means we don't mess with the
> intentions of the cloud operator which were manually specified via
> service-disable.
> I asked on #openstack-nova and got confirmation that this made sense.
> Hooray!  Dare I suggest we are finally coming close to a consensus?

I'm sure we can find more to argue over if we put our minds to it :-)

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