[occi-wg] OCCI MC - State Machine Diagram
Roger Menday
roger.menday at uk.fujitsu.com
Wed May 13 08:40:39 CDT 2009
>
>
>> The resource publishes which states it
>> can transition to at any point, (in this respect quite similar to the
>> changing list of actuator URIs), but the state transition is
>> triggered
>> by creating a new resource in the states collection.
>>
>> Thoughts ?
>
> I am not feeling comfortable with having a state model which
> will change on the fly, depending what a resource will
> answer. For one thing, it will make user interfaces and
> tools really difficult to design:
>
> - should I add a suspend button, even if it works only sometimes?
> - if it worked once, will it work again?
> - what can I do if it does not work? I want to suspend,
> dammit! ;-)
I don't share your pessimism, but then again, I also think we are
getting our wires crossed. I think there is a lot of help here from
hateoas which does a lot to address your concerns above (??)
Roger
>
> Cheers, Andre.
>
>>
>> regards,
>> Roger
>>
>>> I would like to follow up on the state model thread, even if
>>> people seem to have mostly agreed upon the version
>>> documented in the wiki (http://forge.ogf.org/short/occi-wg/states)
>>>
>>> I am really unhappy with a number of things:
>>>
>>> - too many states
>>> - too many state transitions with no actions (i.e.
>>> methods) attached
>>> - unclear entry and exit points
>>>
>>> Please allow me to elaborate
>>>
>>> (1) Too many states:
>>>
>>> All the XXX-ING states (STARTING, SUSPENDING, RESUMING,
>>> STOPPING) seem to have no real benefit, apart from
>>> informing the client that a state transition is in
>>> progress. State transitions, however, should, IMHO, not be
>>> part of a state diagram, unless specific actions can be
>>> performed during that transition.
>>>
>>> For example the STOPPING state: there are no actions
>>> attached to that state, the client can do nothing but wait
>>> until the state reached STOPPED.
>>>
>>> So, why not going to STOPPED immediately, and adding the
>>> transition process to the semantics of the STOPPED state?
>>> (e.g., "resources can still be utilized iff they are
>>> required to store or retrieve the VM state").
>>>
>>>
>>> (2) Too many internal state transitions
>>>
>>> That is related to (1) of course: the diagram has 11
>>> internal state transitions (no actions attached), and 5
>>> external transitions (actions attached)....
>>>
>>> Well, that is not exactly incorrect or anything, but it is
>>> confusing matters. A state model should help to clarify
>>> what actions cause what state change.
>>>
>>>
>>> (3) unclear entry and exit points
>>>
>>> There is no state where the client can be sure that no
>>> remote resources are utilized anymore - i.e., an
>>> 'Destroyed' state is missing. At some point, a client
>>> needs to have the ability to free remote resources (well,
>>> unless one has garbage collection, but we don't want to go
>>> there, right?)
>>>
>>> STOPPED is not really the same - a STOPPED state can be
>>> moved to STARTING/ACTIVE via start(), so the backend cannot
>>> be allowed to free the resources.
>>>
>>>
>>> I do understand that the XXX-ING states are useful for
>>> informative purposes, for example, to allow a GUI to inform
>>> the user that a start() request has been received, and the
>>> backend is spinning up the machine. Those types of
>>> information can, however, easily provided by additional
>>> attributes, or sub-states.
>>>
>>> Attached is an alternate state diagram. It's main purpose
>>> is to illustrate that, by limiting the number of states and
>>> internal state transitions, one can derive a much simplier
>>> (and IMHO cleaner) state diagram.
>>>
>>> Cheers, Andre.
>>>
>>>
>>> PS.: Sorry for not using graffle. Sources are in xfig, so I
>>> don't attach them - don't want to get laughed at for using
>>> such ancient technology ;-)
>>>
>>>
>>> Quoting [Edmonds, AndrewX] (Apr 20 2009):
>>>>
>>>> Updated...
>>>>
>>>> -----Original Message-----
>>>>
>>>> I agree - this is fine with me.
>>>>
>>>> On Mon, 2009-04-20 at 14:02 +0100, Edmonds, AndrewX wrote:
>>>>> Sounds like a good comprise J
>>>>>
>>>>>
>>>>>
>>>>> From: Sam Johnston [mailto:samj at samj.net]
>>>>> Sent: 20 April 2009 13:52
>>>>> To: Edmonds, AndrewX
>>>>> Cc: Thijs.Metsch at Sun.COM; occi-wg at ogf.org; Molino, VictorX M
>>>>> Subject: Re: [occi-wg] OCCI MC - State Machine Diagram
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> I'd tend to side with Thijs on this one - having a complete state
>>>>> machine is a lot less important when the implementation can tell
>>>>> its
>>>>> clients what the next states are (and the humans what they mean in
>>>>> plain $LANGUAGE). That said, if you want to add a dotted loop back
>>>>> to
>>>>> the start then that might help the perfectionists sleep easy.
>>>>>
>>>>> Sam
>>>>>
>>>>> On Mon, Apr 20, 2009 at 2:47 PM, Edmonds, AndrewX
>>>>> <andrewx.edmonds at intel.com> wrote:
>>>>>
>>>>> Then conceptually, how do we recover from an error state if we've
>>>>> exited? Also if we want to support error state recovery, should
>>>>> the
>>>>> state model reflect this?
>>>>>
>>>>>
>>>>> -----Original Message-----
>>>>> From: Thijs.Metsch at Sun.COM [mailto:Thijs.Metsch at Sun.COM]
>>>>> Sent: 20 April 2009 13:42
>>>>> To: Sam Johnston
>>>>> Cc: Edmonds, AndrewX; occi-wg at ogf.org; Molino, VictorX M
>>>>> Subject: Re: [occi-wg] OCCI MC - State Machine Diagram
>>>>>
>>>>> As I stated before maybe we an add another exit-point instead of a
>>>>> real
>>>>> state.
>>>>>
>>>>> Cheers,
>>>>>
>>>>> -Thijs
>>>>>
>>>>>
>>>>> On Mon, 2009-04-20 at 14:39 +0200, Sam Johnston wrote:
>>>>>> On Mon, Apr 20, 2009 at 2:29 PM, Edmonds, AndrewX
>>>>>> <andrewx.edmonds at intel.com> wrote:
>>>>>> I updated the state model (attached) to include an error
>>>>>> state. Couldn???t see how to delete attachments so maybe
>>>>> someone
>>>>>> here has better luck? I also began to add identifiers to
>>>>> each
>>>>>> process transition but the diagram started to become
>>>>> cluttered
>>>>>> so left them out.
>>>>>>
>>>>>>
>>>>>> I would suggest that it's better to keep this clean (though I'm
>>>>>> impressed that you got as far as you did!). You can reach an
>>>>>> error
>>>>>> state from anywhere - if a machine is found to be corrupt even
>>>>>> while
>>>>>> stopped then a STOPPED->ERROR transition makes sense for example.
>>>>>>
>>>>>> Sam
>>>>>>
>>>>>> From: occi-wg-bounces at ogf.org
>>>>> [mailto:occi-wg-bounces at ogf.org]
>>>>>> On Behalf Of Sam Johnston
>>>>>> Sent: 20 April 2009 11:56
>>>>>> To: Tino Vazquez
>>>>>> Cc: occi-wg at ogf.org; Molino, VictorX M; Thijs Metsch
>>>>>>
>>>>>>
>>>>>> Subject: Re: [occi-wg] OCCI MC - State Machine Diagram
>>>>>>
>>>>>>
>>>>>> Hi Tino,
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> A lot of this is covered in the state registry (which I'll
>>>>>> copy below for you) but comments inline nonetheless.
>>>>>>
>>>>>> On Mon, Apr 20, 2009 at 12:35 PM, Tino Vazquez
>>>>>> <tinova at fdi.ucm.es> wrote:
>>>>>>
>>>>>> Howdy everyone,
>>>>>>
>>>>>> Excellent thread. My three cents:
>>>>>>
>>>>>> 1) I think we should define clearly the semantics of the
>>>>>> states. for
>>>>>> instance, what is the difference between STOPPED and
>>>>>> SUSPENDED? Is it
>>>>>> that with SUSPENDED the state is saved and not with STOPPED?
>>>>>>
>>>>>>
>>>>>> Yes, it's exactly that. From the state registry: STOPPED =
>>>>>> "The resource is inactive and has no saved state" and
>>>>>> SUSPENDED="The resource is inactive and has saved state"
>>>>>>
>>>>>>
>>>>>>
>>>>>> 2) I really think we need an entry state like
>>>>>> "PENDING" or "DEFINED".
>>>>>> It will help in implementation relying on a
>>>>>> best-effort scheduler to
>>>>>> match VMs and hosts, like EC2 does. This will be the
>>>>>> state where
>>>>>> machines will wait for a host to be available to run
>>>>>> on. Also, I don't
>>>>>> really think that a machine entering its life cycle
>>>>> in
>>>>>> SUSPENDED state
>>>>>> is a good idea.
>>>>>>
>>>>>>
>>>>>> I tend to agree, but I'd like the terminology to be
>>>>> completely
>>>>>> unambiguous... something like "NEW" [for this AS].
>>>>>>
>>>>>>
>>>>>>
>>>>>> 3) +1 to the "CRASHED", "ERROR" or "FAILED" state.
>>>>>>
>>>>>>
>>>>>> ABORT[ING|ED] = "The resource encountered an error and is
>>>>>> aborting/has aborted".
>>>>>>
>>>>>>
>>>>>> What do you think?
>>>>>>
>>>>>>
>>>>>> Some of these transitions take a while so some way of
>>>>>> indicating progress (especially interesting for long tasks
>>>>>> like live migrations) would be useful. Would prefer a
>>>>>> mechanism that worked universally for the API.
>>>>>>
>>>>>> Sam
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> Extensions
>>>>>> State control
>>>>>> State
>>>>>>
>>>>>>
>>>>>> Transitions
>>>>>>
>>>>>>
>>>>>> Description
>>>>>>
>>>>>>
>>>>>> aborting
>>>>>>
>>>>>>
>>>>>> aborted
>>>>>>
>>>>>>
>>>>>> The resource
>>>>>> encountered an error
>>>>>> and is aborting
>>>>>>
>>>>>>
>>>>>> aborted
>>>>>>
>>>>>>
>>>>>> n/a
>>>>>>
>>>>>>
>>>>>> The resource
>>>>>> encountered an error
>>>>>> and has aborted
>>>>>>
>>>>>>
>>>>>> active
>>>>>>
>>>>>>
>>>>>> pause, restart,
>>>>>> stop, suspend
>>>>>>
>>>>>>
>>>>>> The resource is
>>>>>> active
>>>>>>
>>>>>>
>>>>>> resuming
>>>>>>
>>>>>>
>>>>>> aborting, active
>>>>>>
>>>>>>
>>>>>> The resource is
>>>>>> becoming active and
>>>>>> restoring state
>>>>>>
>>>>>>
>>>>>> pausing
>>>>>>
>>>>>>
>>>>>> aborting, paused
>>>>>>
>>>>>>
>>>>>> The resource is
>>>>>> preparing to refuse
>>>>>> new requests
>>>>>>
>>>>>>
>>>>>> paused
>>>>>>
>>>>>>
>>>>>> aborting, resume
>>>>>>
>>>>>>
>>>>>> The resource is
>>>>>> refusing new
>>>>>> requests
>>>>>>
>>>>>>
>>>>>> starting
>>>>>>
>>>>>>
>>>>>> aborting, active
>>>>>>
>>>>>>
>>>>>> The resource is
>>>>>> becoming active
>>>>>>
>>>>>>
>>>>>> stopped
>>>>>>
>>>>>>
>>>>>> start
>>>>>>
>>>>>>
>>>>>> The resource is
>>>>>> inactive and has no
>>>>>> saved state
>>>>>>
>>>>>>
>>>>>> stopping
>>>>>>
>>>>>>
>>>>>> stopped, aborting
>>>>>>
>>>>>>
>>>>>> The resource is
>>>>>> becoming inactive
>>>>>> and destroying state
>>>>>>
>>>>>>
>>>>>> suspended
>>>>>>
>>>>>>
>>>>>> resume, stop
>>>>>>
>>>>>>
>>>>>> The resource is
>>>>>> inactive and has
>>>>>> saved state
>>>>>>
>>>>>>
>>>>>>
>>>>>> Note: Stable states and user transitions in bold.
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>> -------------------------------------------------------------
>>>>>> Intel Ireland Limited (Branch)
>>>>>> Collinstown Industrial Park, Leixlip, County Kildare,
>>>>> Ireland
>>>>>> Registered Number: E902934
>>>>>>
>>>>>> This e-mail and any attachments may contain confidential
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>>>>>> the sole use of the intended recipient(s). Any review or
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>>>>>> by others is strictly prohibited. If you are not the
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>>>>>> recipient, please contact the sender and delete all copies.
>>>>>>
>>>>>> _______________________________________________
>>>>>> occi-wg mailing list
>>>>>> occi-wg at ogf.org
>>>>>> http://www.ogf.org/mailman/listinfo/occi-wg
>>>>> --
>>>>> Thijs Metsch Tel: +49 (0)941 3075-122
>>>>> (x60122)
>>>>> http://blogs.sun.com/intheclouds
>>>>> Software Engineer Grid Computing
>>>>> Sun Microsystems GmbH
>>>>> Dr.-Leo-Ritter-Str. 7 mailto:thijs.metsch at sun.com
>>>>> D-93049 Regensburg http://www.sun.com
>>>>>
>>>>> -------------------------------------------------------------
>>>>> Intel Ireland Limited (Branch)
>>>>> Collinstown Industrial Park, Leixlip, County Kildare, Ireland
>>>>> Registered Number: E902934
>>>>>
>>>>> This e-mail and any attachments may contain confidential material
>>>>> for
>>>>> the sole use of the intended recipient(s). Any review or
>>>>> distribution
>>>>> by others is strictly prohibited. If you are not the intended
>>>>> recipient, please contact the sender and delete all copies.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> -------------------------------------------------------------
>>>>> Intel Ireland Limited (Branch)
>>>>> Collinstown Industrial Park, Leixlip, County Kildare, Ireland
>>>>> Registered Number: E902934
>>>>>
>>>>> This e-mail and any attachments may contain confidential material
>>>>> for
>>>>> the sole use of the intended recipient(s). Any review or
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>>>>> by others is strictly prohibited. If you are not the intended
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>>> --
>>> Nothing is ever easy.
>>> <occi-states.pdf>_______________________________________________
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>>> http://www.ogf.org/mailman/listinfo/occi-wg
>>
>>
>> Roger Menday (PhD)
>> <roger.menday at uk.fujitsu.com>
>>
>> Senior Researcher, Fujitsu Laboratories of Europe Limited
>> Hayes Park Central, Hayes End Road, Hayes, Middlesex, UB4 8FE, U.K.
>> Tel: +44 (0) 208 606 4534
>>
>>
>> ______________________________________________________________________
>>
>> Fujitsu Laboratories of Europe Limited
>> Hayes Park Central, Hayes End Road, Hayes, Middlesex, UB4 8FE
>> Registered No. 4153469
>>
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>
>
>
> --
> Nothing is ever easy.
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Roger Menday (PhD)
<roger.menday at uk.fujitsu.com>
Senior Researcher, Fujitsu Laboratories of Europe Limited
Hayes Park Central, Hayes End Road, Hayes, Middlesex, UB4 8FE, U.K.
Tel: +44 (0) 208 606 4534
______________________________________________________________________
Fujitsu Laboratories of Europe Limited
Hayes Park Central, Hayes End Road, Hayes, Middlesex, UB4 8FE
Registered No. 4153469
This e-mail and any attachments are for the sole use of addressee(s) and
may contain information which is privileged and confidential. Unauthorised
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e-mail has been scanned by Trendmicro Interscan and McAfee Groupshield does
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