Re: [sca-assembly] [Issue 253]: (1.2) Must a global domain channel bedeployed before it can be used?

[Mike Edwards <mike_edwards@uk.ibm.com>]

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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Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU