constraints

[William Reade]

On Thu, 2013-02-07 at 11:04 +0000, roger peppe wrote:
> William's approach (instance type overrides other
> attributes) is simpler and quite attractive, but has
> the issue that instance-type is "infectious" - if you
> specify an instance type at environment level,
> all attributes in service constraints *other* than instance type
> will be ignored. Thus you'd be forced to use non-portable
> instance types rather than the more appropriate memory
> and cpu attributes. If there were more provider-specific
> attributes than just instance-type, the problem could
> become worse still.

Quick note before I pop out: instance-type doesn't affect *every* other
possible constraint; just cpu/cores/mem.