[openstack-dev] [Murano][Heat] MuranoPL questions?

Stan Lagun slagun at mirantis.com
Wed Mar 19 21:30:14 UTC 2014

On Wed, Mar 19, 2014 at 11:57 PM, Steven Dake <sdake at redhat.com> wrote:

>  Now because DSL provides not only a way to write sandboxed isolated code
> but also a lot of declarations (classes, properties, parameters,
> inheritance and contracts) that are mostly not present in Python we don't
> need Parameters or Output sections in Object Model because all of this can
> be inferred from resource (classes) DSL declaration. Another consequence is
> that most of the things that can be written wrong in HOT can be verified on
> client side by validating classes' contracts without trying to deploy the
> stack and then go through error log debugging. Because all resources'
> attributes types their constraints are known in advance (note that resource
> attribute may be a reference to another resource with constraints on that
> reference like "I want any (regular, Galera etc) MySQL implementation") UI
> knows how to correctly compose the environment and can point out your
> mistakes at design time. This is similar to how statically typed languages
> like C++/Java can do a lot of validation at compile time rather then in
> runtime as in Python.
>  Personally I would love to see many of this features in HOT. What is
> your vision on this? What of the mentioned above can be contributed to
> Heat? We definitely would like to integrate more with HOT and eliminate all
> duplications between projects. I think that Murano and Heat are
> complimentary products that can effectively coexist. Murano provides access
> to all HOT features and relies on Heat for most of its activities. I
> believe that we need to find an optimal way to integrate Heat, Murano,
> Mistral, Solum, Heater, TOSCA, do some integration between ex-Thermal and
> Murano Dashboard, be united regarding Glance usage for metadata and so on.
> We are okay with throwing MuranoPL out if the issues it solves would be
> addressed by HOT.
>   I am not a fan of language features such as inheritance, classes,
> properties, etc.  I get that for a really general purpose language like
> python they are useful.  Python has a multi-year learning curve before
> writing really "pythonic" code.  Hot has a few day learning curve before
> writing really "hotonic" code :)
> I understand your concerns. But is not the case when you need to write
programs using classes and all that stuff. We just using OOP approach to
describe composition. Just because OOP is known to be most efficient way of
component composition. Environments consist of applications. Applications
may consist of application-specific services (for multi-node applications),
VMs, network resources etc. All of this are classes in Murano terminology
and it can be mapped to resources/resource properties/templates in HOT.
Also don't forget that TOSCA has all of this OOP things as well.

90% of classes may consist of 0-2 lines of code. Also note that in Murano
end users do not write code at all. It is not DevOps tools. It is software
engineer who write MuranoPL code. End-user doesn't do anything outside UI

> On Wed, Mar 19, 2014 at 8:06 AM, Steven Dake <sdake at redhat.com> wrote:
>> Ruslan,
>> Some of my thoughts on the evolution of the HOT DSL to date.
>> On 03/18/2014 05:32 PM, Ruslan Kamaldinov wrote:
>>> Here is my 2 cents:
>>> I personally think that evolving Heat/HOT to what Murano needs for it's
>>> use
>>> cases is the best way to make PaaS layer of OpenStack to look and feel
>>> as a
>>> complete and fully integrated solution.
>>> Standardising these things in a project like TOSCA is another direction
>>> we all
>>> should follow. I think that TOSCA is the place where developers (like
>>> us),
>>> application developers and enterprises can collaborate to produce a
>>> common
>>> standard for application lifecycle management in the clouds.
>>> But before Murano contributors jump into direction of extending HOT to
>>> the goal
>>> of application (or system) lifecycle management, we need an agreement
>>> that this
>>> is the right direction for Heat/HOT/DSL and the Orchestration program.
>>> There are
>>> a lot of use cases that current HOT doesn't seem to be the right tool to
>>> solve.
>>> As it was said before, it's not a problem to collaborate on extending it
>>> those
>>> use cases. I'm just unsure if Heat team would like these use cases to be
>>> solved
>>> with Heat/HOT/DSL. For instance:
>>> - definition of an application which is already exposed via REST API.
>>> Think of
>>>    something like Sahara (ex. Savanna) or Trove developed in-house for
>>> internal
>>>    company needs. app publishers wouldn't be happy if they'll be forced
>>> to
>>>    develop a new resource for Heat
>>> - definition of billing rules for an application
>>> If everyone agrees that this is the direction we all should follow, that
>>> we
>>> should expand HOT/DSL to that scope, that HOT should be the answer on
>>> "can you
>>> express it?", then awesome - we can start speaking about implementation
>>> details.
>>> If it's not the direction these projects should follow then at least
>>> finding
>>> where Heat ends and Murano starts to avoid any functionality duplication
>>> would
>>> be great.
>>  The HOT DSL for the most part, either by design or subconscious
>> development choices, enables the application of Miller's Law[1] in a
>> positive way.  HOT as a DSL takes less then a few hours to learn and use
>> effectively.  Its relative simplicity is its *key* advantage as a DSL.
>>  DSL's by their very nature declare a desired state.  It is the
>> responsibility of the DSL processor to convert that desired state into
>> reality.  On a fundamental level, this is precisely what Heat does.
>> A DSL by its very definition is meant to express a desired outcome
>> without specifying the intermediate steps.  To express the intermediate
>> steps would require recording state in variables and offering conditional
>> operations on those variables.  This implies individual steps in the
>> processing of the input to the language.  If HOT were to add these sorts of
>> features, it would no longer be a DSL, but a general purpose language
>> (perhaps less general purpose then python or C).  A DSL is by definition a
>> declarative language. I don't like the idea of expanding the scope of HOT
>> to add an imperative model of operation.
>> Learning imperative languages takes inordinately more time and brainpower
>> then learning declarative languages, especially those which generally
>> follow the advantages provided by languages operating inside the
>> constraints of Miller's Law.  We want Heat to be dead simple to explain and
>> learn.  Realistically I'd like folks to be able to write a template in
>> under an hour with 15 minutes of explanation, and I think we have hit that
>> mark.
>> The idea of expanding the scope of the Heat APIs and engine to include
>> ALM and Workflow don't make sense to me from an engineering perspective.
>>  It over-complicates the code base.  I know we have already covered those
>> thoughts in detail on the mailing list previously and the Murano folks
>> agree that is a bad idea.
>> I see a parallel between expanding the scope of HOT to support ALM and
>> Workflow and expanding the scope of the heat-engine in the same fashion
>> that is not appealing.  What would make more sense is to follow the general
>> laws of Unix (do one thing, do it well) and layer these other possibly
>> imperative languages on top of Heat using HOT and the Heat APIs to
>> implement such imperative programming models. Then if someone really wanted
>> to invest in the complexity of ALM or Workflow, they may be more willing to
>> invest in learning the complexity of a new imperative programming language.
>> My personal opinion is expanding the scope of HOT to include imperative
>> programming models is not desirable for Heat in isolation.  I understand
>> such an outcome may be appealing as a holistic approach to handling the
>> entire orchestration space, but feel the costs of learning an imperative
>> model for HOT do not pay for the advantages of having only one language to
>> program all the things.
>> I see no issue with HOT remaining simple and tidy focused entirely on
>> orchestration (taking a desired state and converting that into reality)
>> with some other imperative language layered on top to handle workflow and
>> ALM.  I believe this separation of concerns is best for OpenStack and
>> should be the preferred development path.
>> Regards,
>> -steve
>> [1]
>> http://en.wikipedia.org/wiki/The_Magical_Number_Seven,_Plus_or_Minus_Two
>>> Thanks,
>>> Ruslan
>>> On Wed, Mar 19, 2014 at 2:07 AM, Keith Bray <keith.bray at rackspace.com>
>>> wrote:
>>>> Georgy,
>>>> In consideration of the "can you express it" instead of the "who will
>>>> generate it," I see Heat's HOT evolving to support the expression of
>>>> complex
>>>> multi-tier architectures and applications (I would argue you can
>>>> already do
>>>> this today, perhaps with some additional features desired, e.g. Ability
>>>> to
>>>> define cloud workflows and workflow execution rules which could come
>>>> when we
>>>> have a workflow service like Mistral).  Therefore, I would encourage
>>>> Murano
>>>> contributors to consider whether they can help make Heat sufficiently
>>>> cover
>>>> desired use cases.  I have never viewed Heat templates as isolated
>>>> components of a multi-tier architecture.  Instead, a single template or
>>>> a
>>>> combination of master/subordinate templates together (using references,
>>>> nesting, or inclusion) could express the complete architecture, both
>>>> infrastructure and applications.
>>>> If I've read your previous comments and threads correctly, you desire a
>>>> way
>>>> to express System Lifecycle Management across multiple related
>>>> applications
>>>> or components, whereby you view the System as a grouping of
>>>> independently
>>>> developed and/or deployed (but systematically related) "components,"
>>>> whereby
>>>> you view Components as individual disconnected Heat templates that
>>>> independently describe different application stacks of the System.  Did
>>>> I
>>>> get that correct?   If so, perhaps the discussion here is one of
>>>> "scope" of
>>>> what can or should be expressed in a Heat template. Is it correct to
>>>> state
>>>> that your argument is that a separate system (such as Murano) should be
>>>> used
>>>> to express System Lifecycle Management as I've defined it here?  If so,
>>>> why
>>>> could we not use the Heat DSL to also define the System?  The System
>>>> definition could be logically separated out into its own text file...
>>>> But,
>>>> we'd have a common DSL syntax and semantics for both lower level and
>>>> higher
>>>> level component interaction (a building block effect of sorts).
>>>> As for "who will generate it," ( with "it" being the Heat multi-tier
>>>> application/infrastructure definition) I think that question will go
>>>> through
>>>> a lot more evolution and could be any number of sources: e.g. Solum,
>>>> Murano,
>>>> Horizon, Template Author with a text editor, etc.
>>>> Basically, I'm a +1 for as few DSLs as possible. I support the position
>>>> that
>>>> we should evolve HOT if needed vs. having two separate DSLs that are
>>>> both
>>>> related to expressing application and infrastructure semantics.
>>>> Workflow is quite interesting ... Should we be able to express
>>>> imperative
>>>> workflow semantics in HOT?  Or, should we only be able to declare
>>>> workflow
>>>> configurations that get configured in a service like Mistral whereby
>>>> Mistral's execution of a workflow may need to invoke Heat hooks or Stack
>>>> Updates?  Or, some other solution?
>>>> I look forward to a design discussion on all this at the summit... This
>>>> is
>>>> fun stuff to think about!
>>>> -Keith
>>>> From: Georgy Okrokvertskhov <gokrokvertskhov at mirantis.com>
>>>> Reply-To: "OpenStack Development Mailing List (not for usage questions)"
>>>> <openstack-dev at lists.openstack.org>
>>>> Date: Tuesday, March 18, 2014 1:49 PM
>>>> To: "OpenStack Development Mailing List (not for usage questions)"
>>>> <openstack-dev at lists.openstack.org>
>>>> Subject: Re: [openstack-dev] [Murano][Heat] MuranoPL questions?
>>>> I see this in the following way - who will generate HOT template for my
>>>> complex multi-tier applications when I have only templates for
>>>> components?
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> --
> Sincerely yours
> Stanislav (Stan) Lagun
> Senior Developer
> Mirantis
> 35b/3, Vorontsovskaya St.
> Moscow, Russia
> Skype: stanlagun
> www.mirantis.com
> slagun at mirantis.com
> _______________________________________________
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Sincerely yours
Stanislav (Stan) Lagun
Senior Developer
35b/3, Vorontsovskaya St.
Moscow, Russia
Skype: stanlagun
slagun at mirantis.com
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