[openstack-dev] [Heat] HOT software configuration refined after design summit discussions

Alex Heneveld alex.heneveld at cloudsoftcorp.com
Tue Nov 12 17:42:54 UTC 2013

Thanks Steve, Zane, Mike.  I withdraw the $idea ... for now (*).

As a user who wants to move away from fiddling with infrastructure I 
like where this is going.  :)


(*)  If there start to be lots of get_param usages and other keywords 
then perhaps $this -- and requiring $$ escapes -- or similar will become 
a good thing but it's hardly needed now, esp if aim is to preserve 
backwards compatibility.

On 12/11/2013 16:43, Steven Hardy wrote:
> On Tue, Nov 12, 2013 at 01:59:35PM +0000, Alex Heneveld wrote:
>> This new proposal [1] looks like a very positive change on top of
>> [2].  Simpler both to read and write.
> Agreed, thanks Thomas for taking the time to write this up, it looks like a
> good reflection of what was discussed last week to me.
>> One minor suggestion is to consider using a special character (eg $)
>> rather than reserved keywords.  As I understand it the keywords are
>> only interpreted when they exactly match the value of a key in a
>> map, so it is already unlikely to be problematic.  However I think
>> it would be more familiar and clear if we instead used the rule that
>> any item (key or value) which _starts_ with a $ is interpreted
>> specially.  What those rules are is TBD but you could for instance
>> write functions -- as either `$get_param('xxx')` or `$get_param:
>> xxx` -- as well as allow accessing a parameter directly `$xxx `.
> So, there has been some discussion on this topic related to the str_replace
> usage of $ prefixes.  In the end we decided straight string replacement was
> better in that case, see:
> https://review.openstack.org/#/c/47772/
> I'm -1 on any backwards incompatible HOT syntax changes at this point,
> unless they can be very strongly justified - we did add a disclaimer to the
> Havana release notes saying HOT was an unstable in-progress format, but
> people will be using it nevertheless.
> If possible, I'd prefer to focus on adding stuff to enable the
> software-config functionality to work, in as backwards-compatible way as is
> practical.
> Steve
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