[Engine-devel] [Design for 3.2 RFE] Improving proxy selection algorithm for Power Management operations

[Yair Zaslavsky]

----- Original Message -----
> From: "Itamar Heim" <iheim at redhat.com>
> To: "Simon Grinberg" <simon at redhat.com>
> Cc: "engine-devel" <engine-devel at ovirt.org>
> Sent: Monday, November 12, 2012 12:21:57 PM
> Subject: Re: [Engine-devel] [Design for 3.2 RFE] Improving proxy selection algorithm for Power Management operations
> 
> On 11/12/2012 12:01 PM, Simon Grinberg wrote:
> >
> >
> > ----- Original Message -----
> >> From: "Dan Kenigsberg" <danken at redhat.com>
> >> To: "Eli Mesika" <emesika at redhat.com>
> >> Cc: "engine-devel" <engine-devel at ovirt.org>
> >> Sent: Monday, November 12, 2012 11:47:14 AM
> >> Subject: Re: [Engine-devel] [Design for 3.2 RFE] Improving proxy
> >> selection algorithm for Power Management operations
> >>
> >> On Sun, Nov 11, 2012 at 06:18:53AM -0500, Eli Mesika wrote:
> >>>
> >>>
> >>> ----- Original Message -----
> >>>> From: "Eli Mesika" <emesika at redhat.com>
> >>>> To: "Itamar Heim" <iheim at redhat.com>
> >>>> Cc: "engine-devel" <engine-devel at ovirt.org>
> >>>> Sent: Friday, November 9, 2012 12:06:05 PM
> >>>> Subject: Re: [Engine-devel] [Design for 3.2 RFE] Improving proxy
> >>>> selection algorithm for Power Management operations
> >>>>
> >>>>
> >>>>
> >>>> ----- Original Message -----
> >>>>> From: "Itamar Heim" <iheim at redhat.com>
> >>>>> To: "Eli Mesika" <emesika at redhat.com>
> >>>>> Cc: "engine-devel" <engine-devel at ovirt.org>, "Michael
> >>>>> Pasternak"
> >>>>> <mpastern at redhat.com>, "Simon Grinberg"
> >>>>> <sgrinber at redhat.com>, "Dan Kenigsberg" <danken at redhat.com>
> >>>>> Sent: Friday, November 9, 2012 12:02:37 PM
> >>>>> Subject: Re: [Engine-devel] [Design for 3.2 RFE] Improving
> >>>>> proxy
> >>>>> selection algorithm for Power Management operations
> >>>>>
> >>>>> On 11/09/2012 10:52 AM, Eli Mesika wrote:
> >>>>>
> >>>>>>>>
> >>>>>>>>   > FenceWrapper
> >>>>>>>>
> >>>>>>>> i understand danken suggested going this way, rather than
> >>>>>>>> than
> >>>>>>>> another
> >>>>>>>> instance of vdsm.
> >>>>>>>> is vdsm only calling these scripts today and all logic is
> >>>>>>>> in
> >>>>>>>> engine,
> >>>>>>>> or
> >>>>>>>> does vdsm has any logic in wrapping these scripts (not a
> >>>>>>>> blocker
> >>>>>>>> to
> >>>>>>>> doing FenceWrapper, just worth extracting that logic from
> >>>>>>>> vdsm
> >>>>>>>> to
> >>>>>>>> such a
> >>>>>>>> script, then using it in both. i hope answer is 'no
> >>>>>>>> logic'...)
> >>>>>> vdsm has some logic that maps between the call passed to it
> >>>>>> from
> >>>>>> engine and the actual parameters generated for the script.
> >>>>>> AFAIK, this logic only "builds" the correct arguments for the
> >>>>>> command according to the agent type
> >>>>>>
> >>>>>
> >>>>> can we extract it to an external wrapper?
> >>>>> I'd hate to fix bugs/changes twice for this.
> >>>>
> >>>> I'll check it with danken on SUN
> >>>
> >>> Well, looked at it a bit , the VDSM code is in fenceNote function
> >>> in API.py
> >>> What I think is that we can exclude the fenceNote implementation
> >>> to
> >>> a separate fence.py file and call it from the API.py
> >>> Then we can use one of the following in Java to call the method
> >>> from fence.py
> >>> 1) jython
> >>> 2) org.python.util.PythonInterpreter
> >>>
> >>> See
> >>> http://stackoverflow.com/questions/8898765/calling-python-in-java
> >>>
> >>> danken, what do you think ?
> >>
> >> BTW, no one has promised the the fence script is implemented in
> >> Python
> >>
> >> $ file `which fence_ipmilan `
> >> /usr/sbin/fence_ipmilan: ELF 64-bit LSB executable...
> >
> > PS, if it's really that complex I don't see the a big issue
> > dropping engine fence
> > It is mostly useful when you have small number of hosts, or
> > collection of small clusters where the admin limits the hosts that
> > are allowed to fence to cluster hosts and as a failsafe the
> > 'engine'

Not sure if this is that complex, I would personally be glad to get more information on the nature of these fence scripts.
Basically, we have several "patterns" for external invocation:
a. Use ScriptEngine - but we must know the type
b. Exec process
c. JNI/JNA

And - in many java enterprise applications options A and C are implemented on a separate Java process (if it crashes, the jvm that runs the enterprise application does not crash) - but I don't think this approach is viable for 3.2.


> >
> > *It does however solves at the same time the issue that we (still)
> > can't 'Approve a host have been rebooted' if it's the last host in
> > the DC since the path goes through the fencing logic.
> 
> exactly, we need to allow engine fence to solve the single/last host
> private case.
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