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

Steven Dake sdake at redhat.com
Wed Mar 19 19:57:43 UTC 2014

On 03/19/2014 02:00 AM, Stan Lagun wrote:
> Steven,
> Agree with your opinion on HOT expansion. I see that inclusion of 
> imperative workflows and ALM would require major Heat redesign and 
> probably would be impossible without loosing compatibility with 
> previous HOT syntax. It would blur Heat mission, confuse current users 
> and rise a lot of questions what should and what should not be in 
> Heat. Thats why we chose to built a system on top of Heat rather then 
> expending HOT.


> Now I would like to clarify why have we chosen imperative approach 
> with DSL.
> You see a DSL as an alternative to HOT but it is not. DSL is 
> alternative to Python-encoded

Not accurate.  I see a HOT as one type of DSL.  I see the MuranoPL as an 
imperative language which is not a DSL.  It may have domain specific 
aspects, but it is more general purpose in nature.

> resources in Heat (heat/engine/resources/*.py). Imagine how Heat would 
> look like if you let untrusted users to upload Python plugins to Heat 
> engine and load them on the fly. Heat resources are written in Python 
> which is imperative language. So that MuranoPL for the same reason.
agree this is bad idea.

> We want application authors to be able to express application 
> deployment and maintenance logic of any complexity. This may involve 
> communication with 3rd party REST services (APIs of applications being 
> deployed, external services like DNS server API, application licensing 
> server API, billing systems, some hardware component APIs etc) and 
> internal OpenStack services like Trove, Sahara, Marconi and others 
> including those that are not incubated yet and those to come in the 
> future. You cannot have such things in HOT and when you required to 
> you need to develop custom resource in Python. Independence  on custom 
> plugins is not good for Murano because they cannot be uploaded by end 
> users and thus he cannot write application definition that can be 
> imported to/run on any cloud and need to convince cloud administrator 
> to install his Python plugin (something that is unimaginable in real 
> life).

I understand.  I am not critical of imperative approach for implementing 
workflow/ALM.  I believe it is mandatory.  I hold no opinion on MuranoPL 

> Because DSL is a way to write custom resources (in Heats terminology) 
> it has to be Turing-complete and have all the characteristics of 
> general-purpose language. It also has to have domain-specific features 
> because we cannot expect that DSL users would be as skilled as Heat 
> developers and could write such resources without knowledge on hosting 
> engine architecture and internals.
I understand your point of view, but DSLs are declarative in nature.  I 
think the problem is that the terminology being used is incorrect as 
computer science has defined it :)  Just because MuranoPL has custom 
stuff for interacting with custom resources, doesn't mean its a DSL.  I 
can draw a parallel between implementing arbitrary length integers in a 
general purpose imperative language. Said feature is not a DSL, it is a 
language feature.

What is being discussed in the context of murano is a language feature, 
rather then a DSL.

> HOT DSL is declarative because all the imperative stuff is hardcoded 
> into Heat engine. Thus all is left for HOT is to define "state of the 
> world" - desired outcome. That is analogous to Object Model in Murano 
> (see [1]). It is Object Model that can be compared to HOT, not DSL. As 
> you can see it not more complex than HOT. Object Model is what 
> end-user produces in Murano. And he event don't need to write it cause 
> it can be composed in UI.
> 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 :)

> If you have a vision on how HOT can address the same domain MuranoPL 
> does or any plans for such features in upcoming Heat releases I would 
> ask you to share it.
> [1] https://wiki.openstack.org/wiki/Murano/DSL/Blueprint#Object_model
I don't think HOT can do these things and I don't think we want HOT to 
do these things.  I am ok with that, since I don't see the pushback on 
having two languages for two different things in OpenStack.  I got from 
gokrove on iRC today that the rationale for the pushback was the TC 
wanted Murano folks to explore how to integrate better with Heat and 
possibly the orchestration program. I don't see HOT as a place where 
there is an opportunity for scope expansion.  I see instead Murano 
creating HOT blobs and feeding them to Heat.


> On Wed, Mar 19, 2014 at 8:06 AM, Steven Dake <sdake at redhat.com 
> <mailto: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 <mailto: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
>             <mailto:gokrokvertskhov at mirantis.com>>
>             Reply-To: "OpenStack Development Mailing List (not for
>             usage questions)"
>             <openstack-dev at lists.openstack.org
>             <mailto: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
>             <mailto: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 <http://www.mirantis.com/>
> slagun at mirantis.com <mailto:slagun at mirantis.com>
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