Re: [ovirt-devel] [VDSM] [ENGINE] [RFC] A configuration verb for contexual vdsm operation mode

> On 4 Apr 2017, at 17:26, Dan Kenigsberg <danken(a)redhat.com&gt; wrote: > > On Tue, Apr 4, 2017 at 1:16 PM, Michal Skrivanek > <michal.skrivanek(a)redhat.com&gt; wrote: >> >> On 4 Apr 2017, at 12:10, Roy Golan <rgolan(a)redhat.com&gt; wrote: >> >> >> >> On Tue, Apr 4, 2017 at 12:49 PM Yaniv Kaul <ykaul(a)redhat.com&gt; wrote: >>> >>> On Tue, Apr 4, 2017 at 12:29 PM, Roy Golan <rgolan(a)redhat.com&gt; wrote: >>>> >>>> I'm working on a POC lately on a change to stats collection and retrieval >>>> by VDSM. The moto is to cut all we can from host/vm stats (possibly caps) >>>> and report only core-business stuff to the engine. Engine will retrieve the >>>> rest through a 3rd party provider >>>> >>>> (nevermind what is it atm) >> >> >> I hope it’s the same one as for VM stats, collectd:) >> >>>> >>>> Being backward compatible by design, I have to support 2 API versions for >>>> Host.getStats , '4.1' and '4.2'. >>>> Except from supplying less parameters, I want VDSM to do less stuff. It >>>> doesn't need to sample what it doesn't report. In other words I want >>>> '4.1-sampling' and '4.2-sampling' >>>> >>>> # Introducing 'configuration' Verb: >>>> >>>> As engine knows always(Hosted Engine as well) what cluster version this >>>> host belongs to, it can configure VDSM to operate in cluster version mode. >> >> >> why not running it in parallel for one version? >> >>>> >>>> Host.configure(config={version: 4.2} >>>> >>>> Consider this verb, pre-activating using 'Host.getCaps' to set the >>>> context. >>>> It will set the righjt sampling method, and other stuff if needed then >>>> API endpoints will have the right permutation of the api to answer it. >>>> >>>> 4.2 host can operate in 4.1 mode: >>>> Host.configure(config={version: 4.1} >>>> >>>> Issue: moving a 4.2 host from 4.2 cluster to 4.1 is a problem since >>>> engine needs to know this is a new vdsm that has the verb available. One way >>>> to overcome that is to fire the verb for every host regardless of the >>>> version and disregard an error that implies the verb doesn't exist. >>> >>> >>> Isn't it solved by host re-installation? >> >> >> We allow maintenance + change host cluster so not always. Was this changed? >>> >>> >>>> >>>> # Engine: >>>> Engine will have a handling of the verb per version. >>>> Host/Vms monitoring should be changed - I suggest to move out of the >>>> monitoring code the whole stats collection as it is a different task which >>>> is orthogonal to 'monitoring' and in 4.2 more than before. >>>> >>>> >>>> I know configuration for VDSM has been discussed before and there are >>>> probably tons of ways to do it. When you share your thoughts please remember >>>> that configuration is a by-product of the effort. >>> >>> >>> How do we persist this level on VDSM? Or we don't, and if VDSM is >>> restarted it is again back to 4.1 mode until Engine tells it otherwise? >>> >>> Y. >> >> >> Must persist it somehow otherwise there is a race when the engine will send >> send a stats request and will get the wrong answer. I'm wondering if using >> differnt endpoints is the right solution here to prevent that from >> happening. >> method: Host.getStats version: 4.1 >> >> >> would it be a problem? assuming that the code is easily started/stopped >> within vdsm, we can just change the behavior based on receiving one or the >> other verb for the first time after vdsm starts > > It does not feel right to have a such a state in Vdsm. and making this > state depend implicitly on a verb feels even worse than an explicit > "configure" verb. We already have something like that in the > debug-oriented setLogLevel verb; but that's not how client/server > applications usually operate. I don’t mind either way > > I think that the proper way to do this would be to reconfigure > vdsm.conf, set there collect_statistics=false (via ovirt-host-deploy > or Anible), and restart vdsmd+supervdsmd. This way we are sure that > all threads and services see the new config and act accordingly. This > can be done by Engine whenever a host is added to a new cluster, based > on the statistic-gathering policy in that cluster. But why would you require restart for such a simple thing? We have the collection pretty well isolated already, it’s not even using periodic sampling, there are nice-to-drop things which can wait (repoStats, HE HA status?)