[jboss-as7-dev] Management proposal for attribute mutability

[Jason T. Greene]

On 8/22/11 1:53 PM, Brian Stansberry wrote:
> On 8/22/11 1:47 PM, Jason T. Greene wrote:
>> On 8/22/11 1:42 PM, Jason T. Greene wrote:
>>> On 8/22/11 1:26 PM, Brian Stansberry wrote:
>>>> On 8/2/11 4:22 PM, Jason T. Greene wrote:
>>>>> Currently we have way too many read only attributes in our management
>>>>> model. This makes life harder for the management tools and/or makes
>>>>> the
>>>>> resulting UI a bit unwieldy.
>>>>>
>>>>> In some cases this is just because we haven't polished subsystem
>>>>> management (PLEASE all subsystem authors look at this!). In other
>>>>> cases
>>>>> though it's intentional because it is either difficult or currently
>>>>> impossible to make hot changes to a particular attribute. This
>>>>> should be
>>>>> exceedingly rare. Users love hot updates, and it's a competitive
>>>>> advantage. So first we should strive to make it hot in the first
>>>>> place.
>>>>>
>>>>> However in the case that the change is not hot, and a server reboot is
>>>>> too aggressive, we should still supporting making the changes by
>>>>> bouncing all services involved. After some debate on IRC we finally
>>>>> arrived at what is IMO a really good option for this problem:
>>>>>
>>>>> write-attribute (impact-services=true|false)
>>>>>
>>>>> The operation handler on such a non-hot attribute would then return an
>>>>> error
>>>>
>>>> A handler should not return an error if a change cannot be applied to
>>>> the runtime. An OperationStepHandler should use the relevant API on the
>>>> OperationContext. E.g. for a handler registered for Stage.RUNTIME:
>>>>
>>>> @Override
>>>> public void execute(OperationContext context, ModelNode operation) {
>>>>
>>>> context.runtimeUpdateSkipped();
>>>> context.reloadRequired(); // or context.restartRequired();
>>>> if (context.completeStep() ==
>>>> OperationContext.ResultAction.ROLLBACK)
>>>> {
>>>> context.revertReloadRequired();
>>>> // or context.revertRestartRequired();
>>>> }
>>>> }
>>>
>>> Well in my above comment I was referring to a problem where a full
>>> server reload and/or restart is too aggressive (i.e. why bounce the web
>>> server when all you want to do is bounce a datasource). So the issue is
>>> that these attributes don't fit that problem.
>>
>> To further clarify the reason to return the error is that the change to
>> the configuration model is NOT APPLIED. If you touch the config without
>> the runtime, then you are out of sync and the only reasonable action to
>> take from that point on is to restart the server. In this case we are
>> saying that changing an attribute could have hostile consequences
>> (bouncing a connection pool therby affecting inbound transactions), and
>> so we need some sort of confirmation by the admin that they really
>> intend to do this.
>>
>
> I see. Seems this eliminates the ability to make a bunch of config
> changes without affecting the runtime and then bouncing the server to
> have them take effect.

Yeah that's a good point. I didn't think of that.

>
> It sounds like you are looking for 3 possible values for this attribute
>
> true -- bounce the affected services
> false -- apply to config, put server in restart-required state
> undefined??? -- user made a mistake, return an error

Hmmm, yes I guess you could say there are three states:

ALLOW_SERVICE_RESTART (affects in-flight transactions)
DELAY_RESTART_UNTIL_NEXT_BOOT
REJECT_SERVICE_RESTART

On the other hand REJECT_SERVICE_RESTART is really a form of safety 
checking / "babying" that could be pushed to the client, as long as we 
had some kind of metadata to tell them the change affects in-flight 
transactions.



-- 
Jason T. Greene
JBoss AS Lead / EAP Platform Architect
JBoss, a division of Red Hat