[Engine-devel] SSH Soft Fencing

[Eli Mesika]

----- Original Message -----
> From: "Livnat Peer" <lpeer at redhat.com>
> To: "Yair Zaslavsky" <yzaslavs at redhat.com>
> Cc: engine-devel at ovirt.org
> Sent: Sunday, June 30, 2013 8:06:28 AM
> Subject: Re: [Engine-devel] SSH Soft Fencing
> 
> On 06/30/2013 05:46 AM, Yair Zaslavsky wrote:
> > 
> > 
> > ----- Original Message -----
> >> From: "Barak Azulay" <bazulay at redhat.com>
> >> To: "Martin Perina" <mperina at redhat.com>
> >> Cc: "Yair Zaslavsky" <yzaslavs at redhat.com>, engine-devel at ovirt.org, "Eli
> >> Mesika" <emesika at redhat.com>
> >> Sent: Thursday, June 27, 2013 8:31:35 PM
> >> Subject: Re: SSH Soft Fencing
> >>
> >>
> >>
> >> ----- Original Message -----
> >>> From: "Eli Mesika" <emesika at redhat.com>
> >>> To: "Yair Zaslavsky" <yzaslavs at redhat.com>
> >>> Cc: "Martin Perina" <mperina at redhat.com>, engine-devel at ovirt.org, "Barak
> >>> Azulay" <bazulay at redhat.com>
> >>> Sent: Thursday, June 27, 2013 5:55:29 PM
> >>> Subject: Re: SSH Soft Fencing
> >>>
> >>>
> >>>
> >>> ----- Original Message -----
> >>>> From: "Yair Zaslavsky" <yzaslavs at redhat.com>
> >>>> To: "Eli Mesika" <emesika at redhat.com>
> >>>> Cc: "Martin Perina" <mperina at redhat.com>, engine-devel at ovirt.org, "Barak
> >>>> Azulay" <bazulay at redhat.com>
> >>>> Sent: Thursday, June 27, 2013 5:43:17 PM
> >>>> Subject: Re: SSH Soft Fencing
> >>>>
> >>>>
> >>>>
> >>>> ----- Original Message -----
> >>>>> From: "Eli Mesika" <emesika at redhat.com>
> >>>>> To: "Martin Perina" <mperina at redhat.com>
> >>>>> Cc: engine-devel at ovirt.org, "Yair Zaslavsky" <yzaslavs at redhat.com>,
> >>>>> "Barak
> >>>>> Azulay" <bazulay at redhat.com>
> >>>>> Sent: Thursday, June 27, 2013 3:48:39 PM
> >>>>> Subject: Re: SSH Soft Fencing
> >>>>>
> >>>>>
> >>>>>
> >>>>> ----- Original Message -----
> >>>>>> From: "Martin Perina" <mperina at redhat.com>
> >>>>>> To: engine-devel at ovirt.org
> >>>>>> Cc: "Yair Zaslavsky" <yzaslavs at redhat.com>, "Barak Azulay"
> >>>>>> <bazulay at redhat.com>, "Eli Mesika" <emesika at redhat.com>
> >>>>>> Sent: Thursday, June 27, 2013 1:51:06 PM
> >>>>>> Subject: SSH Soft Fencing
> >>>>>>
> >>>>>> Hi,
> >>>>>>
> >>>>>> SSH Soft Fencing is a new feature for 3.3 and it tries to restart
> >>>>>> VDSM
> >>>>>> using SSH connection on non responsive hosts prior to real fencing.
> >>>>>> More info can be found at
> >>>>>>
> >>>>>> http://www.ovirt.org/Automatic_Fencing#Automatic_Fencing_in_oVirt_3.3
> >>>>>>
> >>>>>> In current SSH Soft Fencing implementation the restart VDSM using SSH
> >>>>>> command is part of standard fencing implementation in
> >>>>>> VdsNotRespondingTreatmentCommand. But this command is executed only
> >>>>>> if a host has a valid PM configuration. If host doesn't have a valid
> >>>>>> PM configuration, the execution of the command is disabled and host
> >>>>>> state is change to Non Responsive.
> >>>>>>
> >>>>>> So my question are:
> >>>>>>
> >>>>>> 1) Should SSH Soft Fencing be executed on hosts without valid PM
> >>>>>>    configuration?
> >>>>>
> >>>>> I think that the answer should be yes. The vdsm restart will solve most
> >>>>> of
> >>>>> problems , so why not using it whether a PM agent is defined or not.
> >>>> I agree.
> >>>> I would like to say that I also don't like the fact that
> >>>> VdsNotRespondingTreatment extends RestartVdsCommand.
> >>>> One should ask if "non responding treatment is a restart vds operation"
> >>>> or
> >>>> maybe RestartVdsCommand is just a step in the non responding treatment
> >>>> (inheritance vs containment/delegation).
> >>>> I think that VdsNotRespodingTreatment should delegate the call to
> >>>> RestartVdsCommand as the 2nd step after issuing the Soft Fencing
> >>>> command.
> >>>> Thoughts anyone?
> >>>
> >>> That would be a nice and needed re-factoring
> >>
> >> I would say yes - but would add it only with appropriate configuration
> >> (enableAutoSoftVdsmRestartWhenNoPMAvailable .... I hate the name)
> > 
> > +1 on configuration.
> > Configuration must reside at host-related entities (i.e - VdsStatic).
> > 
> > Yair
> > 
> 
> Why would a user like to avoid fencing VDSM when host becomes
> non-responsive?
> 
> I think that adding another configuration option is cumbersome with no
> real value.

I totally agree with Livnat here , restarting vdsm may resolve problems and is much less brutal that host restart, should be implemented without any configuration IMHO

> 
> Livnat
> 
> >>
> >>  
> >>
> >>>
> >>>>
> >>>>>
> >>>>>>
> >>>>>> 2) Should VDSM restart using SSH command be reimplemented
> >>>>>>    as standalone command to be usable also in other parts of engine?
> >>>>>>    If 1) is true, I think it will have to be done anyway.
> >>>>
> >>>> I agree here.
> >>>>>
> >>>>> +1
> >>
> >> On one hand it makes sense,  but I have several questions on the above:
> >> - Who do we think may want to use such a command ?
> >> - Should (or even can) we limit the use of such command to
> >> noneResponsiveTreatment ?
> >>
> >> Having general commands available to all code when there is only one
> >> specific
> >> case we are using it might be a bit riskey,
> >> Especially when we talk about restarting something.
> >>
> >> Thoughts ?
> >>
> >>
> >>
> >>>>>
> >>>>>>
> >>>>>>
> >>>>>> Martin Perina
> >>>>>>
> >>>>>
> >>>>
> >>>
> >>
> > _______________________________________________
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> > Engine-devel at ovirt.org
> > http://lists.ovirt.org/mailman/listinfo/engine-devel
> > 
> 
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