Re: [Engine-devel] Autorecovery feature plan for review

From: "Moran Goldboim" <mgoldboi(a)redhat.com&gt; To: "Yaniv Kaul" <ykaul(a)redhat.com&gt; Cc: engine-devel(a)ovirt.org Sent: Thursday, February 16, 2012 10:01:37 AM Subject: Re: [Engine-devel] Autorecovery feature plan for review On 02/16/2012 09:35 AM, Yaniv Kaul wrote: > On 02/16/2012 09:29 AM, Moran Goldboim wrote: >> On 02/16/2012 12:38 AM, Itamar Heim wrote: >>> On 02/15/2012 07:02 PM, Livnat Peer wrote: >>>> On 15/02/12 18:28, Ayal Baron wrote: >>>>> >>>>> >>>>> ----- Original Message ----- >>>>>> Hi, >>>>>> >>>>>> A short summary from the call today, please correct me if I >>>>>> forgot or >>>>>> misunderstood something. >>>>>> >>>>>> Ayal argued that the failed host/storagedomain should be >>>>>> reactivated >>>>>> by a periodically executed job, he would prefer if the engine >>>>>> could >>>>>> [try to] correct the problem right on discovery. >>>>>> Livnat's point was that this is hard to implement and it is OK >>>>>> if we >>>>>> move it to Nonoperational state and periodically check it >>>>>> again. >>>>>> >>>>>> There was a little arguing if we call the current behavior a >>>>>> bug >>>>>> or a >>>>>> missing behavior, I believe this is not quite important. >>>>>> >>>>>> I did not fully understand the last few sentences from Livant, >>>>>> did we >>>>>> manage to agree in a change in the plan? >>>>> >>>>> A couple of points that we agreed upon: >>>>> 1. no need for new mechanism, just initiate this from the >>>>> monitoring context. >>>>> Preferably, if not difficult, evaluate the monitoring data, >>>>> if >>>>> host should remain in non-op then don't bother running >>>>> initVdsOnUp >>>>> 2. configuration of when to call initvdsonup is orthogonal to >>>>> auto-init behaviour and if introduced should be on by default >>>>> and >>>>> user should be able to configure this either on or off for the >>>>> host in general (no lower granularity) and can only be >>>>> configured >>>>> via the API. >>>>> When disabled initVdsOnUp would be called only when admin >>>>> activates the host/storage and any error would keep it inactive >>>>> (I >>>>> still don't understand why this is at all needed but whatever). >>>>> >>>> >>>> Also a note from Moran on the call was to check if we can unify >>>> the >>>> non-operational and Error statuses of the host. >>>> It was mentioned on the call that the reason for having ERROR >>>> state is >>>> for recovery (time out of the error state) but since we are >>>> about to >>>> recover from non-operational status as well there is no reason >>>> to have >>>> two different statuses. >>> >>> they are not exactly the same. >>> or should i say, error is supposed to be when reason isn't >>> related >>> to host being non-operational. >>> >>> what is error state? >>> a host will go into error state if it fails to run 3 >>> (configurable) >>> VMs, that succeeded running on other host on retry. >>> i.e., something is wrong with that host, failing to launch VMs. >>> as it happens, it already "auto recovers" for this mode after a >>> certain period of time. >>> >>> why? because the host will fail to run virtual machines, and will >>> be >>> the least loaded, so it will be the first target selected to run >>> them, which will continue to fail. >>> >>> so there is a negative scoring mechanism on number of errors, >>> till >>> host is taken out for a while. >>> >>> (I don't remember if the reverse is true and the VM goes into >>> error >>> mode if the VM failed to launch on all hosts per number of >>> retries. >>> i think this wasn't needed and user just got an error in audit >>> log) >>> >>> i can see two reasons a host will go into error state: >>> 1. monitoring didn't detect an issue yet, and host would >>> have/will/should go into non-operational mode. >>> if host will go into non-operational mode, and will auto recover >>> with the above flow, i guess it is fine. >>> >>> 2. cause for failure isn't something we monitor for (upgraded to >>> a >>> bad version of qemu, or qemu got corrupted). >>> >>> now, the error mode was developed quite a long time ago (august >>> 2007 >>> iirc), so could be it mostly compensated for the first reason >>> which >>> is now better monitored. >>> i wonder how often error state is seen due to a reason which >>> isn't >>> monitored already. >>> moran - do you have examples of when you see error state of >>> hosts? >> >> usually it happened when there were a problematic/ misconfigurated >> vdsm / libvirt which failed to run vms (nothing we can recover >> from)- >> i haven't faced the issue of "host it too loaded" that status has >> some other syndromes, however the behaviour on that state is very >> much the same -waiting for 30 min (?) and than move it to >> activated. >> Moran. > > 'host is too loaded' is too loaded is the only transient state > where a > temporary 'error' state makes sense, but in the same time, it can > also > fit the 'non operational' state description. > From my experience, the problem with KVM/libvirt/VDSM > mis-configured > is never temporary, (= magically solved by itself, without concrete > user intervention). IMHO, it should move the host to an error state > that would not automatically recover from. > Regardless, consolidating the names of the states ('inactive, > detached, non operational, maintenance, error, unknown' ...) would > be > nice too. Probably can't be done for all, of course. > Y. agreed, most of the causes of ERROR state aren't transient, but looks to me as if this state is redundant and could be taken care as part of the other host states, since the way it's being used today isn't very helpful as well. Moran.

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