[Engine-devel] SSH Soft Fencing

[Livnat Peer]

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.

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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