Null provider and failing early

[Tim Penhey]

On 27/08/13 13:41, David Cheney wrote:
> I think they should be ignored, but preserved.

What is your thinking on this?  Why would we want to ignore them?

I have my ideas why, but I'm wondering what others think.

These are obviously the two choices we have:
 * Fail
 * Ignore

Tim

> 
> On Tue, Aug 27, 2013 at 11:40 AM, Tim Penhey <tim.penhey at canonical.com> wrote:
>> On 27/08/13 11:50, Andrew Wilkins wrote:
>>> On Tue, Aug 27, 2013 at 8:44 AM, Tim Penhey <tim.penhey at canonical.com
>>> <mailto:tim.penhey at canonical.com>> wrote:
>>>
>>>     Perhaps we should have a sanity-check type callback into the provider
>>>     with the constraints at the time we want to add a machine.  This would
>>>     give the null provider the early fail mechanism, and could also allow
>>>     other providers to error if people as asking for constraints that really
>>>     don't make sense.
>>>
>>>
>>> I'm sort of thinking out aloud here: maybe this could used for checking
>>> environment-specific constraints too? Some kind of
>>> "VerifyMachineConstraints" method that will ensure your add-machine/--to
>>> constraints are valid for the current provider/environment. In this case
>>> constraints may be nil, but the null provider would just always return
>>> false.
>>
>> This is exactly what I'm thinking as well, but I had forgotten about the
>> provider specific constraints.
>>
>> It does raise the question of what should happen if a provider specific
>> constraint is passed to a provider that can't handle it.  My suggestion
>> is we fail.
>>
>> Tim
>>
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