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Subject: Re: [sca-assembly] [NEW ISSUE] Assembly specification unclear onContribution vs Deployment - when can errors in artifacts be reported?


See responses inline.

   Simon

Jim Marino wrote:
> hi,
> 
> Sorry for the delay in responding ot this but I have been traveling and 
> without a properly functioning internet connections. I do have comments 
> inline but I have the feeling that we are lacking definitions of the 
> various contribution states. I'll define two states to clarify my 
> comments below:
> 
> 1. When a contribution is in the installed state, its exports are 
> visible in the domain and deployables are ready for deployment
> 2. When a contribution is in the deployed state, its components are 
> available to service a request on one or more runtimes in the domain
> 
> Jim
> 
> On Jun 5, 2009, at 4:51 AM, Simon Nash wrote:
> 
>> See comments inline below.
>>
>>  Simon
>>
>> Jim Marino wrote:
>>> On Jun 2, 2009, at 5:28 AM, Simon Nash wrote:
>>>> Jim Marino wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>> > >> in sca-contribution.xml files within a Contribution. If an 
>>>>>>> artifact   > >> is deployed which has dependencies
>>>>>>> > >> on other artifacts, then those dependent artifacts are also 
>>>>>>> deployed.
>>>>>>> > >> When the SCA runtime has one or more deployable artifacts, 
>>>>>>> the   > >> runtime attempts to put those artifacts
>>>>>>> > >> and any artifacts they depend on into the Running state.  
>>>>>>> This can   > >> fail due to errors in one or more of the artifacts
>>>>>>> > >> or the process can be delayed until all dependencies are 
>>>>>>> available.
>>>>>>> > >> 11.3.1
>>>>>>> > >> Checking for errors in artifacts MUST NOT be done for 
>>>>>>> artifacts in   > >> the Installed state (ie where the artifacts are
>>>>>>> > >> simply part of installed contributions] {ASM120xx]
>>>>>>> > > This seems over-restrictive.  For example, what about 
>>>>>>> malformed   > > artifacts
>>>>>>> > > such as .composite files with XML syntax errors?  It might be 
>>>>>>> useful   > > to
>>>>>>> > > inform the user about such problems when the artifacts are   
>>>>>>> > > installed, but
>>>>>>> > > the proposed rule would apparently prohibit an SCA runtime 
>>>>>>> from even
>>>>>>> > > discovering these problems at installation time.  I think a 
>>>>>>> better   > > rule
>>>>>>> > > would be to allow such errors to be detected as long as this 
>>>>>>> does not
>>>>>>> > > prevent any artifacts from being deployed.  For example: Any 
>>>>>>> errors in
>>>>>>> > > artifacts in the Installed state (i.e., where the artifacts 
>>>>>>> are part   > > of
>>>>>>> > > installed contributions and have not been deployed) MUST NOT 
>>>>>>> prevent   > > the
>>>>>>> > > SCA runtime from deploying artifacts.
>>>>>>> > >
>>>>>>> >
>>>>>>> > I agree with the general statement that runtimes should be 
>>>>>>> allowed to   > detect syntactic errors upfront since that is what 
>>>>>>> users would expect   > and want (i.e. contributions should not be 
>>>>>>> installed if they contain   > invalid artifacts). However, I 
>>>>>>> don't follow the part about not   > preventing artifacts from 
>>>>>>> being deployed. Is it the case that an error   > in some random 
>>>>>>> contribution artifact A, does not prevent a composite C   > in 
>>>>>>> the same contribution from being deployed? Many users would want 
>>>>>>> to   > prevent that scenario. For example, I would expect most 
>>>>>>> users would   > only want "clean" contributions in a production 
>>>>>>> environment.
>>>>>>> >
>>>>>>> I think (I hope) what Simon means is that it's ok for a runtime to
>>>>>>> detect errors at install time (if possible and reasonable) as 
>>>>>>> long as
>>>>>>> it's also possible to go ahead and deploy those artifacts even when
>>>>>>> the deployment engine knows there are errors in the artifacts.
>>>>>> In Jim's scenario above, if A has a known error but C does not have
>>>>>> a known error, I think compliant runtimes should be allowed to deploy
>>>>>> C if requested.  I am leaning towards going further and saying that
>>>>>> compliant runtimes should be required to deploy C if requested.
>>>>>>
>>>>> I think requiring runtimes to deploy artifacts from contributions 
>>>>> that contain known errors would be very a bad thing to do. Here's why:
>>>>> 1. Most users have stringent regulation over production 
>>>>> environments and do not permit application artifacts containing 
>>>>> detectable errors to be deployed. In most cases I have seen, this 
>>>>> also goes for development environments. For example, good 
>>>>> development environments have mechanisms in place to verify 
>>>>> artifacts such as integration tests that fail a build if an error 
>>>>> is detected. This avoids accumulating broken artifacts and cruft in 
>>>>> source repositories.  Requiring a compliant runtime to make a 
>>>>> contribution containing detectable errors available in a domain 
>>>>> would negate being able to lock down a production or development 
>>>>> environment in this way.  2. The random artifact A could be 
>>>>> exported by the contribution. It is possible for a composite 
>>>>> contained in another contribution to be deployed at some later date 
>>>>> that references artifact A. The error in A will surface at that 
>>>>> later point. I think most people would prefer the error to be 
>>>>> raised at the time the contribution containing A was "installed" in 
>>>>> the domain. 3. It's very difficult to calculate with absolute 
>>>>> certainty that contribution C does not indirectly reference A, 
>>>>> particularly if A can be located dynamically in code. Providing 
>>>>> fail-fast behavior avoids runtime errors from surfacing where they 
>>>>> can cause more damage. I do agree compliant runtimes should be 
>>>>> allowed to deploy contributions containing invalid artifacts. 
>>>>> However, they should not be required to do so.
>>>>>> A more interesting question is if another composite B has a known
>>>>>> error, should compliant runtimes be required or allowed to deploy B
>>>>>> if requested?  I think this depends on the kind of error.  Some
>>>>>> errors might be severe enough to prevent the deployment from
>>>>>> succeeding.  Some errors might be less severe so that it would be
>>>>>> possible to allow deployment, even though some of the resulting
>>>>>> components would not be executable.  The SCA specs should define
>>>>>> which errors fall into which of these categories.
>>>>>>
>>>>> How can a runtime be certain an error in B will not cause a serious 
>>>>> problem if B is deployed? Can you provide examples of such errors? Jim
>>>> An example would be a misplaced Java annotation.  In this case, the
>>>> JavaCAA spec says that the SCA runtime MUST NOT run the component
>>>> which uses the invalid implementation code.  This implies to me that
>>>> other components in the same contribution can be deployed and run.
>>>>
>>>> Simon
>>>>
>>>>
>>> It may be useful to break this down into two parts. First, are you 
>>> saying that it should be possible for a runtime to selectively deploy 
>>> a composite where some components are in error, i.e. only deploy the 
>>> components contained in a composite that do not contain errors? I 
>>> can't imagine a case, even in development, where this would be 
>>> useful. I certainly can't imagine why someone would want this 
>>> behavior in a production environment.
>> In this case, all the components would be deployed, but some of them
>> could not be run.  So if component B has a wire to component C, both
>> B and C are deployed and the wire is valid.  If B then makes an
>> invocation on C, this causes a runtime error.  If B never makes an
>> invocation on C, B is allowed to run with errors.
>>
> I'm not sure I would define C as "deployed" in this scenario. I would 
> describe deployment as the process of making components in a composite 
> available to service requests on one or more runtimes. However, I don't 
> think we need to argue that point at the moment. Regardless of how one 
> defines deployment, in this scenario, B can't be deployed (using either 
> definition of the term) if B's reference to C is required. Since a 
> functioning wire cannot be established, it is not safe for the runtime 
> to allow B to service requests. As a developer of  a service, I would 
> want to know upfront if a wire is not valid. Otherwise, there is no way 
> to determine this without making a service invocation.
> 
As I said in other comments, it should be allowed for SCA runtimes to
operate in this stricter mode.  I believe it should also be allowed
for SCA runtimes to deploy a composite even if some of the components
inside the composite have certain kinds of errors.

>> I see the above behaviour as one that runtimes should be allowed but
>> not required to support.  IMO it would also be valid for a runtime
>> to fail the deployment of the composite containing B and C.
>>
>> Here's my proposal for what should be allowed and required.
>>
>> 1. Runtimes MAY allow contributions to be installed even though
>>   they contain known errors.  In this case, the runtime MAY detect
>>   and report the errors, and MUST perform the installation.
>>
> I don't think the runtime should be required to proceed with the 
> installation as it leads to the same problems I outlined previously. 
> This seems to be in contradiction to statement 2 below, but I am 
> probably reading it incorrectly. I think it is very important that a 
> runtime be allowed to fail an installation if the contribution contains 
> known errors. By contribution installation, I mean the process by which 
> exported contribution artifacts become available for import by other 
> contributions.
> 
I think you might have missed the significance of "In this case"
in the above paragraph.  This was included to signify that the second
sentence only applies if the runtime fulfils the MAY clause, i.e., it
has chosen to allow contributions to be installed even if they contain
errors.  If the runtime does not fulfil the MAY clause (i.e., it has
chosen not to allow contributions to be installed if they contain errors),
the second sentence starting "In this case" would not apply.

>> 2. Runtimes MAY prevent installation of contributions containing
>>   known errors.
>>
>> 3. Some types of errors (defined by the spec) MUST be detected at
>>   deployment time.  In this case the composite containing the
>>   error MUST NOT be deployed, and the installed contribution
>>   containing the composite MUST NOT be uninstalled.
>>
> Sorry, I'm not sure I understand this. Is this saying that the runtime 
> should not attempt uninstallation without operator intervention? 
> Consider the following sequence:
> 
> ---> install contribution ---> deploy composite ---> X error
> 
> There needs to be a way to recover and for a contribution containing an 
> erroneous composite to be uninstalled:
> 
> ---> uninstall ---> install fixed contribution ---> deploy composite 
> ---> success
> 
> The uninstall operation should be a valid operation that can be 
> performed by an administrator/deployer person.
> 
Perhaps my statement was badly worded.  I meant that the discovery
of the error MUST NOT cause the contribution to become uninstalled.
To put this another way, the contribution would still be in the
installed state even though a deployment error has occurred for
one of its composites.  It would of course be possible for an
explicit action to uninstall it subsequently.

>> 4. Some types of errors (defined by the spec) MAY be detected at
>>   deployment time and otherwise MUST be detected at runtime.
>>   If the error is detected at deployment time, the composite
>>   containing the error MUST NOT be deployed, and the installed
>>   contribution containing the composite MUST NOT be uninstalled.
>>   If the error is detected at runtime, the deployed composite
>>   containing the error MUST NOT be undeployed.
>>
> 
> I think this is too vague. Some runtimes (like Fabric3) have the notion 
> of transactional deployment. It should be permissible for "runtime" 
> errors encountered during a deployment to result in a rollback of the 
> domain state to what it was prior to the deployment operation.
> 
I agree, and this is what I thought I had said in my words above.
If the error is detected during deployment, the attempted deployment
MUST NOT occur.  However, if the error is detected at runtime,
the error MUST NOT change the deployment state.

>> 5. Some types of errors (defined by the spec) cannot be detected
>>   at deployment time and MUST be detected at runtime.  In this
>>   case the deployed composite containing the error MUST NOT be
>>   undeployed.
>>
>>> For the second part, we can assume the error is in an artifact not 
>>> used by the composite being deployed. I'll start with a definition:  
>>> when a contribution is in the installed state, its exports are 
>>> visible in the domain and deployables are ready for deployment.
>>> I would expect the type of error identified above to be reported 
>>> upfront when an attempt is made to install the contribution. How can 
>>> a runtime be sure it is safe to install the contribution otherwise - 
>>> i.e. latent errors are ruled out? The only way it is safe is if the 
>>> Java class can never be used as a component implementation. This is 
>>> very difficult to determine at best. In order for this to work, the 
>>> runtime would need to use an algorithm similar to the following:
>>> 1. Determine if the Java class is directly referenceable from outside 
>>> the contribution via an export/import. All applicable export/import 
>>> types must be examined
>>> 2. Introspect all composites and their hierarchies (includes and 
>>> implementation uses) in the contribution to calculate where the Java 
>>> artifact is reachable from
>>> 3. Determine if any of the composites are referenceable from outside 
>>> the contribution via an export/import. All applicable export/import 
>>> types must be examined
>>> If any of these steps result in true, the runtime cannot guarantee 
>>> safety. This algorithm becomes much more complex for other artifacts 
>>> - for example, an artifact referenced by qname several layers deep in 
>>> a hierarchy.  It's also worth noting performing this calculation is 
>>> likely to severely impact install time.
>>> Of course, a runtime could choose not to perform this check and 
>>> install the contribution, throwing an error later if an attempt is 
>>> made to use the artifact.
>> >
>> This would be my preference.  I agree that trying to guarantee safety
>> wouldn't be practical.
>>
>> >               However, I personally wouldn't want to use a runtime that
>>> does that. Consider the following scenario:
>>> 1.  Contribution A is installed with composite C and Java 
>>> implementation J. A exports J's package. C does not reference J. J 
>>> contains an error as described above.
>>> 2.  C is deployed
>>> 3. At a later point in time, contribution B is installed containing 
>>> composite C2. B imports J's package and the runtime resolves the 
>>> import to contribution A's export. C2 uses J as a component 
>>> implementation.
>>> 4. An attempt is made to deploy C2, which surfaces the error in J.
>>> At this point there is a serious problem as the error in J cannot be 
>>> corrected without undeploying C. This could potentially be fixed by 
>>> deploying a new contribution with an updated version of J but if B's 
>>> import were fixed to a specific version of J's package, there is no 
>>> way to guarantee the import will resolve to the contribution export 
>>> containing the fixed version of J. In other words, we have now 
>>> introduced a serious issue in a production environment that is 
>>> entirely avoidable.
>> IMO this is a corner case that is outweighed by the benefit of allowing
>> contributions with errors to be installed.
>>
> 
> I think this happens more frequently than we are lead to believe. In any 
> event, even if it is a corner case, it is important to allow runtimes 
> the opportunity to handle it properly given the serious problems that 
> may arise if it happens.
> 
Again I don't agree with subjective words like "properly" which imply
that one approach is more correct than the other.  As I have said in other
comments, I think both approaches should be allowed, and SCA should not
state or imply that either is better or worse than the other.

>>> One way to avoid this is to put the onus on users to properly 
>>> structure contributions and have good test coverage. In the above 
>>> scenario, A has mixed concerns and should probably be separated into 
>>> distinct contributions.
>> >
>> This would be my preferred solution for the corner case.
>>
>>>               A better way to avoid this is by allowing a runtime to 
>>> report the error upfront and not install contribution A. This won't 
>>> catch all cases (some errors depend on the state of the domain and 
>>> must be detected at deployment), but it will catch a lot of them.
>> I don't think this is "better", but I also don't think SCA should
>> disallow it.
>>
> I think we just are going to need to agree to disagree here. The 
> important thing is the specification should accommodate both approaches 
> and allow implementors the freedom to choose the strategy that best 
> suits their users.
> 
We don't seem to be disagreeing.  It appears we both think that SCA
should allow both the stricter and laxer approaches to error detection.

   Simon

>>> I think we need to take a step back and ask: why would we *require* a 
>>> runtime to deploy a contribution in the above scenario? I'm happy to 
>>> allow runtimes to do this but it should not be the required or 
>>> mandated default behavior. In fact, most people I know would never 
>>> want this to be possible in a production or staging environment. Even 
>>> in development, most people I know want fail-fast behavior because 
>>> they practice iterative development and have lightweight containers 
>>> that boot quickly.
>> My preference for development would be different, but I think SCA
>> should allow runtimes to support either approach.
>>
>>  Simon
>>
>>> Jim
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>>
>>
>>
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> 
> 
> 




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