[Engine-devel] SSH Soft Fencing

[Livnat Peer]

On 06/30/2013 07:35 PM, Barak Azulay 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)
>>
>>  
>>
>>>
>>>>
>>>>>
>>>>>>
>>>>>> 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 ?


I believe you'll agree that right encapsulation and decoupling is part
of writing a maintainable code, it is not necessarily about reusing it.

>> - Should (or even can) we limit the use of such command to
>> noneResponsiveTreatment ?
>>

At this point this command would be executed only within the
noneResponsiveTreatment flow.
We don't need to model this in the REST API nor in the UI, decoupling
the vdsm fencing code is just an internal implementation detail.


>> 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.
> 

I am not sure what is the risk?

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