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On 11/16/2015 04:25 PM, Steven Hardy wrote:
> Hi all,
>
> I wanted to start some discussion re $subject, because it's been apparrent
> that we have a lack of clarity on this issue (and have done ever since we
> started using parameter_defaults).
>
> Some context:
>
> - Historically TripleO has provided a fairly comprehensive "top level"
>    parameters interface, where many per-role and common options are
>    specified, then passed in to the respective ResourceGroups on deployment
>
> https://git.openstack.org/cgit/openstack/tripleo-heat-templates/tree/overcloud-without-mergepy.yaml#n14
>
> The nice thing about this approach is it gives a consistent API to the
> operator, e.g the parameters schema for the main overcloud template defines
> most of the expected inputs to the deployment.
>
> The main disadvantage is a degree of template bloat, where we wire dozens
> of parameters into each ResourceGroup, and from there into whatever nested
> templates consume them.
>
> - When we started adding interfaces (such as all the OS::TripleO::*ExtraConfig*
>    interfaces, there was a need to enable passing arbitrary additional
>    values to nested templates, with no way of knowing what they are (e.g to
>    enable wiring in third-party pieces we have no knowledge of or which
>    require implementation-specific arguments which don't make sense for all
>    deployments.
>
> To do this, we made use of the heat parameter_defaults interface, which
> (unlike normal parameters) have global scope (visible to all nested stacks,
> without explicitly wiring in the values from the parent):
>
> http://docs.openstack.org/developer/heat/template_guide/environment.html#define-defaults-to-parameters
>
> The nice thing about this approach is its flexibility, any arbitrary
> values can be provided without affecting the parent templates, and it can
> allow for a terser implementation because you only specify the parameter
> definition where it's actually used.
>
> The main disadvantage of this approach is it becomes very much harder to
> discover an API surface for the operator, e.g the parameters that must be
> provided on deployment by any CLI/UI tools etc.  This has been partially
> addressed by the new-for-liberty nested validation heat feature, but
> there's still a bunch of unsolved complexity around how to actually consume
> that data and build a coherent consolidated API for user interaction:
>
> https://github.com/openstack/heat-specs/blob/master/specs/liberty/nested-validation.rst
>
> My question is, where do we draw the line on when to use each interface?
>
> My position has always been that we should only use parameter_defaults for
> the ExtraConfig interfaces, where we cannot know what reasonable parameters
> are.  And for all other "core" functionality, we should accept the increased
> template verbosity and wire arguments in from overcloud-without-mergepy.
>
> However we've got some patches which fall into a grey area, e.g this SSL
> enablement patch:
>
> https://review.openstack.org/#/c/231930/46/overcloud-without-mergepy.yaml
>
> Here we're actually removing some existing (non functional) top-level
> parameters, and moving them to parameter_defaults.
>
> I can see the logic behind it, it does make the templates a bit cleaner,
> but at the expense of discoverablility of those (probably not
> implementation dependent) parameters.
>
> How do people feel about this example, and others like it, where we're
> enabling common, but not mandatory functionality?
>
> In particular I'm keen to hear from Mainn and others interested in building
> UIs on top of TripleO as to which is best from that perspective, and how
> such arguments may be handled relative to the capabilities mapping proposed
> here:
>
> https://review.openstack.org/#/c/242439/
>
> Thanks!
>
> Steve
>
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I think I'll try to do a bit of a recap to make sure I understand 
things. It may shift slightly off the topic of this thread but I think 
it is worth it and it will describe what the GUI is able/expecting to 
work with.

Template defines parameters and passes them to child templates via 
resource properties.
Root template parameter values are set by (in order of precedence):
1. 'parameters' param in 'stack create' api call or 'parameters' section 
in environment
2. 'parameter_defaults' section in environment
3. 'default' in parameter definition in template

Non-root template parameter values are set by (in order of precedence):
1. parent resource properties
2. 'parameter_defaults' in environment
3. 'default' in parameter definition in template

The name collisions in parameter_defaults should not be a problem since 
the template author should make sure, the parameters names he defines 
don't collide with other templates.

The GUI's main goal (same as CLI and tripleo-common) is not to hardcode 
anything and use THT (or any other set of files) which user provides as 
a source of all information. It prepares deployment in several steps:
1. Plan Creation - uploads THT files and specifies root template.

2. Environments selection - based on Capabilities map which is provided 
as part of THT (https://review.openstack.org/#/c/242439/) user picks 
which environments he intends to use for deployment.

3. Parameters setting - Based on 2. tripleo-common runs heat template 
validation and input for GUI is nested parameters json structure. The 
output from GUI (through tripleo-common) is a new 'temporary' 
environment which holds values in 'parameters' section for root template 
parameters and values for nested parameters (without 'value') in 
'parameter_defaults' section.

This means that in GUI we'll provide form inputs for every parameter 
from the root template and for the nested parameters which don't have a 
'value' attribute.
The inputs will be pre-filled with 'default' value if parameter has one 
provided (either from param_defaults or parameter definition).

I'll need to do more thinking about how what I describe here is affected 
by what we are trying to solve in $subject...

4. Deploy  - for deployment, all environments are merged: Root 
Environment < Custom Environments < Temporary Environment.


Resource capabilities
I have put some thinking into resource capabilities spec usefulness when 
I was creating the Capabilities map. I think it is much more useful to 
specify multiple Environments which are mutually exclusive and implement 
some functionality's configuration. It seems to be much better to make 
the choice on the environment level rather then resource_registry level, 
because the selection of templates possible to use for implementing some 
resource changes with the environments selected. So resource 
capabilities depend on the Environments selected. So to make really 
simple example, if we have a resource, which can be implemented by 2 
templates, I'd create 2 environments which defines resource_registry 
each with one of the templates available.

What I mean by this is, it is better to let user choose on the 
environment level rather than on resource_registry level. Resource 
capabilities could be valid in terms of providing validation that 
certain template can be used to implement certain resource. Although 
this seems not needed as the creator of Environment should make sure he 
uses template which is able to implement that resource.

I should probably add this to the resource capabilities spec review.


Jirka