I think incremental adoption is a great principle to have and this
will enable that.

So +1

-Rob

On 3 February 2015 at 13:52, Steve Baker <sba...@redhat.com> wrote:
> A spec has been raised to add a config option to allow operators to choose
> whether to use the new convergence engine for stack operations. For some
> context you should read the spec first [1]
>
> Rather than doing this, I would like to propose the following:
> * Users can (optionally) choose which engine to use by specifying an engine
> parameter on stack-create (choice of classic or convergence)
> * Operators can set a config option which determines which engine to use if
> the user makes no explicit choice
> * Heat developers will set the default config option from classic to
> convergence when convergence is deemed sufficiently mature
>
> I realize it is not ideal to expose this kind of internal implementation
> detail to the user, but choosing convergence _will_ result in different
> stack behaviour (such as multiple concurrent update operations) so there is
> an argument for giving the user the choice. Given enough supporting
> documentation they can choose whether convergence might be worth trying for
> a given stack (for example, a large stack which receives frequent updates)
>
> Operators likely won't feel they have enough knowledge to make the call that
> a heat install should be switched to using all convergence, and users will
> never be able to try it until the operators do (or the default switches).
>
> Finally, there are also some benefits to heat developers. Creating a whole
> new gate job to test convergence-enabled heat will consume its share of CI
> resource. I'm hoping to make it possible for some of our functional tests to
> run against a number of scenarios/environments. Being able to run tests
> under classic and convergence scenarios in one test run will be a great help
> (for performance profiling too).
>
> If there is enough agreement then I'm fine with taking over and updating the
> convergence-config-option spec.
>
> [1]
> https://review.openstack.org/#/c/152301/2/specs/kilo/convergence-config-option.rst
>
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-- 
Robert Collins <rbtcoll...@hp.com>
Distinguished Technologist
HP Converged Cloud

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