There is, of course, a small irony here, that we voted to close ASSEMBLY-255 in this weeks call.
Suppose I could, as a deployer of a composite, indicate on all of the components that there must not be any references to GDCs in said components. The redeployment question (and auto-deploy, for that matter) might stand a greater chance of being moot, since the only references to the GDC would come from the wiring of the producers and consumers in the composite that I'm actually working on.
Note an important point - the only point at which we're guaranteed to identify the presence of GDC references is at *deployment* time, where we're guaranteed to have all the mechanism to actually execute the deployment. However, the person doing the design of the composite does not necessarily have all that information at *design* time, when they're connecting producers and consumers up. Since the GDC references aren't part of the componentType, there's no guarantee at *design* time that the GDC references are visible.
By closing out ASSEMBLY-255, we've closed the door to indicating, in the model, that the assembler can restrict that *only* place where GDCs can be referenced is at the "top-level" of deployment (if that's what the assembler chooses). So rather than guaranteeing we can indicate a failure at design-time, we instead might fail long after that, when the deployer contributes the composite to the domain. What we've got prevents problems, but surely isn't very friendly to our end-users.
Only when you're certain that the only uses of GDCs come specifically from the composite being developed, can you be certain that the redeployment question isn't a horrible ugly mess.
-Eric.
On 2/10/11 2:48 AM, Mike Edwards wrote:
OF61762484.8E336A16-ON80257833.00373C0C-80257833.003A9430@uk.ibm.com" type="cite">
Danny,
I'm less about making arguments and more about trying to describe the Event Processing ideas in the same terms that we
have already described for services in the current V1.1 specifications. There, the spec does describe different styles of
runtime, with differing approaches to deployment and to the possibility of redeployment.
I tried to point out that auto-deployment carries an implication of redeployment, since if the runtime auto-deploys some channel
for which there is actually a concrete channel supplied by some later deployment, then we are inevitably into the realm of
redeployment.
Redeployment of a channel is at the least a tricky thing. The same can be said of the redeployment of a service component.
Basically, what happens to anything that is "in flight"? I was trying to address some of these issues for auto-deploy channels in what I wrote.
Now, let me make my position clear on "auto deployment". I think that we have similar behaviour applied in particular to PolicySets,
with the notion that in principle an SCA Runtime can have other mechanisms to supply these things to the Domain, other than by
deploying the contents of one or more Contributions. eg there is the concept of PolicySets being deployed from some kind of
Repository and not necessarily being held in any application Contribution. The current specs don't disallow this, although they
deliberately don't say much about it since the possibilities for implementation are very broad and there is little normative to say.
What it is - is outside the standards.
So, I could envisage auto-deployment along the same lines. Something that any SCA Runtime could choose to provide by some
means, but where the SCA specifications say very little. If an SCA runtime chooses to provide auto-deployment, then it can do so
in any way it wishes.
The downside for an application developer is that their application, as contained in a set of Contributions, may not work on some SCA
runtimes, if the developer/assembler chooses not to contain one or more Domain Channels within their composites, that they rely on
in some components within the application. If they do this, then their application may work fine on an SCA runtime that supports
auto-creation but fail when run with a runtime that does not support auto-creation. The same is true, I note, of PolicySets - if the
application does not supply them, there is no guarantee that they will be made available through some other mechanism by the
SCA runtime.
However, for any SCA Runtime that DOES provide auto-creation, there is a need to describe what happens if, due to the sequence of
deployments, some auto-created channel is "replaced" by the later deployment of a "real channel". In my opinion, it would be wise to
try to avoid such a situation. However, I don't see a way of preventing this situation - perhaps this is something that you'd like to describe.
Yours, Mike
Dr Mike Edwards Mail Point 146, Hursley Park STSM Winchester, Hants SO21 2JN SCA & Services Standards United Kingdom Co-Chair OASIS SCA Assembly TC
IBM Software Group
Phone: +44-1962 818014
Mobile: +44-7802-467431 (274097)
e-mail: mike_edwards@uk.ibm.com
From: Danny van der Rijn <dannyv@tibco.com> To: Mike Edwards/UK/IBM@IBMGB Cc: OASIS Assembly <sca-assembly@lists.oasis-open.org> Date: 09/02/2011 17:34 Subject: Re: [sca-assembly] [Issue 253]: (1.2) Must a global domain channel be deployed before it can be used?
Mike -
Your arguments seem to me to be more arguing against case a) than against autocreation, as they hold for *any* more restrictive redeployment, not just one whose previously deployed state was perhaps auto-deployed.
Auto-deployment (as I envision it) is merely shorthand for an actual deployment. ("Your composite references a global domain channel that hasn't been deployed. Shall I create one for you and deploy it, or would you prefer me to reject deployment of your composite outright?") Your arguments just point out another weakness I see in the concept of global domain channels.
Danny
On 2/9/2011 2:45 AM, Mike Edwards wrote:
Danny,
SCA Runtime "styles";
a) Reconfiguration/Redeployment is allowed
b) Reconfiguration/Redeployment is not allowed
Case b) is the simpler of the two. In this case, all the configuration must be present when the runtime is started.
Either Domain channels are part of the configuration at this point or not - if not, then any references to Domain
channels would either be errors (no auto-creation of channels) or would require auto-creation of channels.
Case a) is the case where there can be separate deployment of (some) consumers & producers and of the
channel(s) that they connect to. I note that this can only happen for Domain level channels. Once separate
deployment is possible, then the timing of deployment matters - if Channel deployment is later than deployment
of any of the producers that connect to the channel, then it the question of auto-creation comes into play.
If no auto-creation is NOT allowed by the runtime, then any event produced will have nowhere to go, which might
be flagged as an error (since the producer is configured to transmit the events). If auto-creation is allowed, then
the events will be flowed to an auto-created Channel and on to whatever consumers are connected to that channel.
When the Channels are later deployed into such a runtime, I assume that the auto-created Channels get "replaced"
by the deployed versions, with whatever configuration they carry. Since the configuration may carry Filters, this may
mean that some events get forwarded by the auto-created channel that don't get forwarded by the specifically
deployed channel. I'm not sure what this would mean for the consumers attached to the channel. More problematic
would be any binding and policy information attached - the binding could indicate the need to have the channel use
some specific existing infrastructure (eg some MQ queue) - and if the intention is that events flow to/from the existing
infrastructure, then the auto-deploy channel is unlikely to do this.
I think the result of this is that during the period when any auto-deploy channels are being used, before the point
where the specifically configured channels are active, that some events may not reach all their intended destination(s)
and some events may not be received by some SCA consumers listening on those channels.
All of which might argue for a process of deploying the Domain channels first, which kind of undermines the idea of
auto-deploying those channels.
Yours, Mike
Dr Mike Edwards Mail Point 146, Hursley Park STSM Winchester, Hants SO21 2JN SCA & Services Standards United Kingdom Co-Chair OASIS SCA Assembly TC
IBM Software Group
Phone: +44-1962 818014
Mobile: +44-7802-467431 (274097)
e-mail: mike_edwards@uk.ibm.com
From: Danny van der Rijn <dannyv@tibco.com> To: Mike Edwards/UK/IBM@IBMGB Cc: sca-assembly@lists.oasis-open.org Date: 08/02/2011 22:02 Subject: Re: [sca-assembly] [Issue 253]: (1.2) Must a global domain channel be deployed before it can be used?
OK, I'll take a stab at answering your question, although I'm just presenting one alternative among many.
First, though, your wording interests me:
in the case where the channel concerned DOES
have configuration and it so happens that the channel is deployed to the Domain some time after some of the
producers and consumers using the channel are deployed to the Domain.
What intrigues me is the notion that your use case allows you to assert that something about the channel's configuration. Can that configuration never change? If so, how would you deal with changing that? By undeploying and redeploying it? Some other means?
I would apply whatever answer you have to that question to this one.
To wit:
Say that you do allow some form of runtime redeployment or modification. So in this case the implementation MAY autodeploy the channel (RFC 2119 wording intentional). If someone chooses to redeploy the channel with further configuration later, so be it. Use whatever form of modification you were going to support in the case where the prior configuration was not auto-deployed.
Say you don't allow modification. Then I'd say that your implementation should either not allow for autodeployment, or that your implementation should put up some reasonable bar to autodeployment.
Danny
On 2/8/2011 1:51 AM, Mike Edwards wrote:
Folks,
I'd appreciate it if someone could explain how things would work in the case where the channel concerned DOES
have configuration and it so happens that the channel is deployed to the Domain some time after some of the
producers and consumers using the channel are deployed to the Domain.
Yours, Mike
Dr Mike Edwards Mail Point 146, Hursley Park STSM Winchester, Hants SO21 2JN SCA & Services Standards United Kingdom Co-Chair OASIS SCA Assembly TC
IBM Software Group
Phone: +44-1962 818014
Mobile: +44-7802-467431 (274097)
e-mail: mike_edwards@uk.ibm.com
From: Anish Karmarkar <Anish.Karmarkar@oracle.com> To: sca-assembly@lists.oasis-open.org Date: 08/02/2011 09:15 Subject: Re: [sca-assembly] [Issue 253]: (1.2) Must a global domain channel be deployed before it can be used?
Danny and Eric's arguments have convinced me that auto-creation of
global channels make sense. It would certainly simplify config/deploy --
I won't have to create a separate composite that contains only the
channel name and then deploy it to the domain. Currently we do allow
this for the default channel ("//"). As Eric points out, my issue wrt
error detection can be dealt with by tools (I can have a global option
or flag for the deployer). Given that we already allow this for the
default channel, and channels currently require no additional
configuration (one can have configuration, but is not required to),
autocreation would provide a consistent model and would make simple
deployment scenarios easier.
-Anish
--
On 2/7/2011 9:50 AM, Eric Johnson wrote:
> To be more explicit, and echo Danny's point, I think we have four options:
>
> 1) Mandate that auto-creation of channels works
> 2) Mandate that auto-creation of channels never works
> 3) Identify specific situations where #1 or #2 are possible
> 4) Take no position (this may still imply changes to the spec, insofar
> as we highlight the point, while taking no sides)
>
> I raised the issue because #4, it seems to me, leaves the door open for
> interoperability failures. ("I deployed X over here with no problems,
> but it doesn't work over there.")
>
> Insofar as I've recall the discussion of the concrete use cases for
> global domain channels (Oracle's F2F presentation), we explicitly noted:
> no filters, no policies, and no bindings on said channels. Meaning,
> configuration optional, and it's just a name. If it is just a name, why
> can't I auto-create?
>
> Anish notes that some people like the safety net of predefined names,
> and I agree that's useful. However, that can be addressed in a variety
> of ways that aren't nearly so heavy-handed as to simply deny the
> deployment. ("The domain contribution includes references to global
> domain channel "foo" that doesn't yet exist. Continue/Cancel?).
>
> -Eric.
>
> On 2/7/11 9:30 AM, Danny van der Rijn wrote:
>> Yet all their configuration is optional?
>>
>> On 2/7/2011 3:39 AM, Mike Edwards wrote:
>>>
>>> Eric,
>>>
>>> My view is that global channels - indeed any channels - are more than
>>> a name - they have configuration associated
>>> with them. A system which does not require them to be declared makes
>>> it difficult to provide required configuration.
>>>
>>> Yours, Mike
>>> ------------------------------------------------------------------------
>>>
>>> Dr Mike Edwards Mail Point 146, Hursley Park
>>> STSM Winchester, Hants SO21 2JN
>>> SCA & Services Standards United Kingdom
>>> Co-Chair OASIS SCA Assembly TC
>>> IBM Software Group
>>> Phone: +44-1962 818014
>>> Mobile: +44-7802-467431 (274097)
>>> e-mail: mike_edwards@uk.ibm.com
>>>
>>>
>>>
>>>
>>>
>>> From: Eric Johnson <eric@tibco.com>
>>> To: Anish Karmarkar <Anish.Karmarkar@oracle.com>
>>> Cc: sca-assembly@lists.oasis-open.org
>>> Date: 04/02/2011 17:14
>>> Subject: Re: [sca-assembly] [Issue 253]: (1.2) Must a global domain
>>> channel be deployed before it can be used?
>>>
>>>
>>> ------------------------------------------------------------------------
>>>
>>>
>>>
>>>
>>> On 2/4/11 1:37 AM, Anish Karmarkar wrote:
>>> > I don't see this being different than say requiring that a variable be
>>> > declared before it is used.
>>> <eej>
>>> Which might be a perfect analogy.
>>>
>>> If the only point of a global channel is to establish a name, then
>>> there's actually minimal value to declaring it before it is used. Many
>>> dynamic languages work this way - Python & Ruby. In the case of global
>>> domain channels, for many use cases, filters and bindings don't make
>>> sense, so the channel just becomes a name. At which point, declaration
>>> before use looks like ceremony over substance.
>>>
>>> </eej>
>>> >
>>> > -Anish
>>> > --
>>> >
>>> > On 2/1/2011 10:11 AM, Danny van der Rijn wrote:
>>> >> An interesting argument for tight coupling...
>>> >>
>>> >> On 2/1/2011 6:19 AM, Anish Karmarkar wrote:
>>> >>> I think this is a fine issue to raise, but I don't quite support the
>>> >>> auto-creation proposal. The only global channel that is
>>> >>> 'auto-deployed' or always exists is the default channel.
>>> >>>
>>> >>> I would want the runtime to tell me if I referenced a channel
>>> that has
>>> >>> not been deployed (unless it is the default channel, which is the
>>> >>> exception). If I want a producer and consumer (especially if they are
>>> >>> in different composites) to communicate over a common channel, I
>>> would
>>> >>> want the system to catch typos. For example, if the producer is
>>> >>> connected to the channel "//omg" and the consumer is connected to
>>> >>> "//zomg", they would be deployed fine but my application would not
>>> >>> work correctly.
>>> >>>
>>> >>> -Anish
>>> >>> --
>>> >>>
>>> >>> On 1/31/2011 10:19 AM, Eric Johnson wrote:
>>> >>>> Hi Peter,
>>> >>>>
>>> >>>> On 1/31/11 10:02 AM, Peter Niblett wrote:
>>> >>>>> Eric
>>> >>>>>
>>> >>>>> You said..
>>> >>>>>
>>> >>>>> Neither of the above indicate whether or not the global domain
>>> >>>>> channel
>>> >>>>> can be used before it is referenced.
>>> >>>>
>>> >>>> Ah yes, the joys of a muddled brain on Monday morning. You're
>>> >>>> correct -
>>> >>>> the question is whether or not the global domain channel can be used
>>> >>>> before it is *created* via a contribution.
>>> >>>>
>>> >>>> Thanks for catching my circularity.
>>> >>>>
>>> >>>> -Eric.
>>> >>>>>
>>> >>>>> I'm not sure how you can "use" a channel without referencing it (I
>>> >>>>> assume "reference" means "wire to/from"), but I think the question
>>> >>>>> you
>>> >>>>> are asking is the one in the title - "can you reference a channel
>>> >>>>> that
>>> >>>>> hasn't been defined to the SCA assembly?". I think this is one
>>> place
>>> >>>>> where the current spec is clear.. you can't reference a domain
>>> >>>>> channel
>>> >>>>> that hasn't been defined.
>>> >>>>>
>>> >>>>> So it looks as though your issue is to say that we should
>>> change the
>>> >>>>> spec to say that it permits (in fact requires) autocreation of
>>> domain
>>> >>>>> channels. Presumably these channels would have to be created with
>>> >>>>> default attributes (though I know you think they shouldn't have
>>> >>>>> attributes at all).
>>> >>>>>
>>> >>>>> Regards
>>> >>>>>
>>> >>>>> Peter Niblett
>>> >>>>> IBM Senior Technical Staff Member
>>> >>>>> Member of the IBM Academy of Technology
>>> >>>>> +44 1962 815055
>>> >>>>> +44 7825 657662 (mobile)
>>> >>>>>
>>> >>>>>
>>> >>>>>
>>> >>>>>
>>> >>>>> From: Eric Johnson<eric@tibco.com>
>>> >>>>> To: OASIS SCA Assembly<sca-assembly@lists.oasis-open.org>
>>> >>>>> Date: 31/01/2011 17:19
>>> >>>>> Subject: [sca-assembly] NEW ISSUE: (1.2) Must a global domain
>>> channel
>>> >>>>> be deployed before it can be used?
>>> >>>>>
>>> ------------------------------------------------------------------------
>>> >>>>>
>>> >>>>>
>>> >>>>>
>>> >>>>>
>>> >>>>>
>>> >>>>> Title: Must a global domain channel be deployed before it can be
>>> >>>>> used?
>>> >>>>>
>>> >>>>> Target: Assembly 1.2 WD 03
>>> >>>>>
>>> >>>>> Description:
>>> >>>>>
>>> >>>>> Via the "@target" and "@source" attributes defined on a consumer&
>>> >>>>> producer, the assembler can reference global domain channels.
>>> >>>>>
>>> >>>>> In section 5.8, the presumed to be normative text reads "SCA
>>> runtimes
>>> >>>>> MUST support the use of domain channels [ASM????]." That is
>>> followed
>>> >>>>> by:
>>> >>>>>
>>> >>>>> "To create a Domain Channel, deploy a composite containing a
>>> channel
>>> >>>>> directly to the SCA Domain (i.e., do not use that composite as the
>>> >>>>> implementation of some component in the Domain)."
>>> >>>>>
>>> >>>>> Neither of the above indicate whether or not the global domain
>>> >>>>> channel
>>> >>>>> can be used before it is referenced.
>>> >>>>>
>>> >>>>> Proposal:
>>> >>>>>
>>> >>>>> General theme: do not require the global domain channel to exist
>>> >>>>> before
>>> >>>>> it can be used.
>>> >>>>>
>>> >>>>> Specific text (needs refinement?):
>>> >>>>>
>>> >>>>> In section 5.8, Paragraph #2, append:
>>> >>>>>
>>> >>>>> When contributing artifacts to a domain that contain references to
>>> >>>>> global domain channels that have not been created, the SCA runtime
>>> >>>>> MUST
>>> >>>>> automatically create said global domain channels, and cannot reject
>>> >>>>> such
>>> >>>>> contributions [ASM????].
>>> >>>>>
>>> >>>>>
>>> >>>>>
>>> >>>>>
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>>> >>>>>
>>> >>>>>
>>> >>>>>
>>> >>>>>
>>> ------------------------------------------------------------------------
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