[Engine-devel] SSH Soft Fencing

[Livnat Peer]

On 06/27/2013 05:43 PM, Yair Zaslavsky wrote:
> 
> 
> ----- 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?
> 

I agree.
The purpose of this feature is to add escalation step when handling non
responsive host.
Power fencing is only a step in the escalation flow. so should be called
from within the main flow controller (the VdsNotRespodingTreatment).

Maybe we'd like this to be fine tuned by a custom policy in future versions.

>>
>>>
>>> 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

+1
The VDSM restart is a step in the escalation flow, and it should not be
tightly coupled with the non-responsive treatment implementation.

>>
>>>
>>>
>>> Martin Perina
>>>
>>
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