Open Stack

With the Icehouse release we announced that there would be no further 
backwards-incompatible changes to HOT without a revision bump. However, 
I notice that we've already made an upward-incompatible change in Juno:

https://review.openstack.org/#/c/102718/

So a user will be able to create a valid template for a Juno (or later) 
version of Heat with the version

   heat_template_version: 2013-05-23

but the same template may break on an Icehouse installation of Heat with 
the "stable" HOT parser. IMO this is almost equally as bad as breaking 
backwards compatibility, since a user moving between clouds will 
generally have no idea whether they are going forward or backward in 
version terms.

(Note: AWS don't use the version field this way, because there is only 
one AWS and therefore in theory they don't have this problem. This 
implies that we might need a more sophisticated versioning system.)

I'd like to propose a policy that we bump the revision of HOT whenever 
we make a change from the previous stable version, and that we declare 
the new version stable at the end of each release cycle. Maybe we can 
post-date it to indicate the policy more clearly. (I'd also like to 
propose that the Juno version drops cfn-style function support.)

cheers,
Zane.