[Engine-devel] SSH Soft Fencing

[Eli Mesika]

----- 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: Sunday, June 30, 2013 7:35:22 PM
> Subject: Re: SSH Soft Fencing
> 
> 
> 
> ----- 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)
> > 
> >  
> > 
> > > 
> > > > 
> > > > > 
> > > > > > 
> > > > > > 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 ?

Yes, I think we should limit that 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.

We can keep this internal and not expose it to the user, just implement explicitly in non responding treatment 

> 
> Martin ? Eli? Yair?
> 
> Can you please refer to the issue above ?
> 
> 
> > 
> > Thoughts ?
> > 
> > 
> > 
> > > > > 
> > > > > > 
> > > > > > 
> > > > > > Martin Perina
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
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