[openstack-dev] [TripleO] Should we have a TripleO API, or simply use Mistral?

Jiri Tomasek jtomasek at redhat.com
Wed Jan 27 17:48:51 UTC 2016

On 01/27/2016 03:36 PM, Dan Prince wrote:
> On Wed, 2016-01-27 at 14:32 +0100, Jiri Tomasek wrote:
>> On 01/26/2016 09:05 PM, Ben Nemec wrote:
>>> On 01/25/2016 04:36 PM, Dan Prince wrote:
>>>> On Mon, 2016-01-25 at 15:31 -0600, Ben Nemec wrote:
>>>>> On 01/22/2016 06:19 PM, Dan Prince wrote:
>>>>>> On Fri, 2016-01-22 at 11:24 -0600, Ben Nemec wrote:
>>>>>>> So I haven't weighed in on this yet, in part because I was
>>>>>>> on
>>>>>>> vacation
>>>>>>> when it was first proposed and missed a lot of the initial
>>>>>>> discussion,
>>>>>>> and also because I wanted to take some time to order my
>>>>>>> thoughts
>>>>>>> on
>>>>>>> it.
>>>>>>>    Also because my initial reaction...was not conducive to
>>>>>>> calm and
>>>>>>> rational discussion. ;-)
>>>>>>> The tldr is that I don't like it.  To explain why, I'm
>>>>>>> going to
>>>>>>> make
>>>>>>> a
>>>>>>> list (everyone loves lists, right? Top $NUMBER reasons we
>>>>>>> should
>>>>>>> stop
>>>>>>> expecting other people to write our API for us):
>>>>>>> 1) We've been down this road before.  Except last time it
>>>>>>> was
>>>>>>> with
>>>>>>> Heat.
>>>>>>>    I'm being somewhat tongue-in-cheek here, but expecting a
>>>>>>> general
>>>>>>> service to provide us a user-friendly API for our specific
>>>>>>> use
>>>>>>> case
>>>>>>> just
>>>>>>> doesn't make sense to me.
>>>>>> We've been down this road with Heat yes. But we are currently
>>>>>> using
>>>>>> Heat for some things that we arguable should be (a workflows
>>>>>> tool
>>>>>> might
>>>>>> help offload some stuff out of Heat). Also we haven't
>>>>>> implemented
>>>>>> custom Heat resources for TripleO either. There are mixed
>>>>>> opinions
>>>>>> on
>>>>>> this but plugging in your code to a generic API is quite nice
>>>>>> sometimes.
>>>>>> That is the beauty of Mistral I think. Unlike Heat it
>>>>>> actually
>>>>>> encourages you to customize it with custom Python actions.
>>>>>> Anything
>>>>>> we
>>>>>> want in tripleo-common can become our own Mistral action
>>>>>> (these get
>>>>>> registered with stevedore entry points so we'd own the code)
>>>>>> and
>>>>>> the
>>>>>> YAML workflows just tie them together via tasks.
>>>>>> We don't have to go off and build our own proxy deployment
>>>>>> workflow
>>>>>> API. The structure to do just about anything we need already
>>>>>> exists
>>>>>> so
>>>>>> why not go and use it?
>>>>>>> 2) The TripleO API is not a workflow API.  I also largely
>>>>>>> missed
>>>>>>> this
>>>>>>> discussion, but the TripleO API is a _Deployment_ API.  In
>>>>>>> some
>>>>>>> cases
>>>>>>> there also happens to be a workflow going on behind the
>>>>>>> scenes,
>>>>>>> but
>>>>>>> honestly that's not something I want our users to have to
>>>>>>> care
>>>>>>> about.
>>>>>> Agree that users don't have to care about this.
>>>>>> Users can get as involved as they want here. Most users I
>>>>>> think
>>>>>> will
>>>>>> use python-tripleoclient to drive the deployment or the new
>>>>>> UI.
>>>>>> They
>>>>>> don't have to interact with Mistral directly unless they
>>>>>> really
>>>>>> want
>>>>>> to. So whether we choose to build our own API or use a
>>>>>> generic one
>>>>>> I
>>>>>> think this point is mute.
>>>>> Okay, I think this is a very fundamental point, and I believe
>>>>> it gets
>>>>> right to the heart of my objection to the proposed change.
>>>>> When I hear you say that users will use tripleoclient to talk
>>>>> to
>>>>> Mistral, it raises a big flag.  Then I look at something like
>>>>> https://github.com/dprince/python-tripleoclient/commit/77ffd2fa
>>>>> 7b1642
>>>>> b9f05713ca30b8a27ec4b322b7
>>>>> and the flag gets bigger.
>>>>> The thing is that there's a whole bunch of business logic
>>>>> currently
>>>>> sitting in the client that shouldn't/can't be there.  There are
>>>>> historical reasons for it, but the important thing is that the
>>>>> current
>>>>> client architecture is terribly flawed.  Business logic should
>>>>> never
>>>>> live in the client like it does today.
>>>> Totally agree here. In fact I have removed business logic from
>>>> python-
>>>> tripleoclient in this patch and moved it into a Mistral action.
>>>> Which
>>>> can then be used via a stable API from anywhere.
>>>>> Looking at that change, I see a bunch of business logic around
>>>>> taking
>>>>> our configuration and passing it to Mistral.  In order for us
>>>>> to do
>>>>> something like that and have a sustainable GUI, that code _has_
>>>>> to
>>>>> live
>>>>> behind an API that the GUI and CLI alike can call.  If we ask
>>>>> the GUI
>>>>> to
>>>>> re-implement that code, then we're doomed to divergence between
>>>>> the
>>>>> CLI
>>>>> and GUI code and we'll most likely end up back where we are
>>>>> with a
>>>>> GUI
>>>>> that can't deploy half of our features because they were
>>>>> implemented
>>>>> solely with the CLI in mind and made assumptions the GUI can't
>>>>> meet.
>>>> The latest feedback I've gotten from working with the UI
>>>> developers on
>>>> this was that we should have a workflow to create the
>>>> environment. That
>>>> would get called via the Mistral API via python-tripleoclient and
>>>> any
>>>> sort of UI you could imagine and would essentially give us a
>>>> stable
>>>> environment interface.
>>> Anything that requires tripleoclient means !GUI though.  I know the
>>> current GUI still has a bunch of dependencies on the CLI, but that
>>> seems
>>> like something we need to fix, not a pattern to repeat.  I still
>>> think
>>> any sentence containing "call Mistral via tripleoclient" is
>>> indicative
>>> of a problem in the design.
>> I am not sure I understand the argument here.
>> Regardless of which API we use (Mistral API or TripleO API) GUI is
>> going
>> to call the API and tripleoclient (CLI) is going to call the API
>> (through mistralclient - impl. detail).
>> GUI can't and does not call API through tripleoclient. This is why
>> the
>> work on extracting the common business logic to tripleo-common
>> happened.
>> So tripleo-common is the place which holds the business logic.
>> The proposed API (in the spec) is supposed only to work as a thin
>> layer
>> that provides the tripleo-common functionality.
>> Most of the operations we do in TripleO are workflows that consists
>> of
>> several requests to various OpenStack services, e.g. Nodes
>> Introspection, deployment progress tracking, etc. Mistral fits as a
>> best
>> tool to use to manage this and provides an API that can be used
>> directly
>> by both CLI and GUI. The work involved is just about turning
>> tripleo-common into Mistral Actions.
>> Alternatives are to create TripleO API and implement our own custom
>> workflows (reinvent the Mistral wheel) as part of  tripleo-common.
>> Or
>> Shield the Mistral API behind a very thin TripleO API. Which in my
>> opinion is not worth it and just adds new layer to the project
>>   > TripleO API > mistralclient > Mistral API > tripleo-common
>> actions)
>> But there are also some operations that do not require a workflow.
>> Such
>> as listing available environments, posting the parameter values and
>> storing them in temporary environment... In those cases the Mistral
>> API
>> does not work as good as TripleO API because Mistral API is able to
>> start a workflow but is not able to take a request and return an
>> immediate response to that request.
> What I did in my demo/prototype was to just use Mistral's generic API
> to update the environment directly. The things we want to store in the
> environment are actually quite simple:
>   -container name (for heat templates)
>   -set of selected heat environments
>   -extra parameters
>   -cached things to help UI select these things like a capabilities map
> Last time we talked on there was interest in creating an "interface"
> around managing creating/updating/deleting these things... and I
> suggested we could use a workflow to do it just the same.
> That isn't my preference, I'm fine with defining these as a loose data
> structure (a set of properties really). If we do it that we you can
> simply use the Mistral REST API to update an environment quite nicely.
> If we prefer a more rigidly defined data structure we could wrap the
> same logic with workflows to manage it. The UI/CLI could still read the
> information directly via the Mistral environments API, and just use a
> workflow to update it. Or we could use workflows for everything. Any
> combination would be possible here.
> Mistral environments are a useful abstraction for workflows. At the end
> of the day nothing would prevent an end user from using mistralclient
> to manage the same thing via a JSON file... But if we really want to
> wrap it with a workflow we really could do that. I think for the simple
> data construct we are talking about here it really is fine to manage as
> just a JSON POST request to Mistral's environments API:
> http://paste.openstack.org/show/485140/
> Dan

So I made more investigation regarding the non-workflow requests and 
thanks to the suggestion from Ryan, I found out, that Mistral supports 
Action Executions which enables us to just call a single action and we 
are able to get the action's output as a response to the requests. Which 
solves the problem for us.

This is IMO a major thing in regards the usability of Mistral as an API 
and it is great that Mistral supports it!

As an example I did listing of keystone services. This is built-in 
mistral action which I could use right away.

parameters: {"name":"keystone.services_list"}

accepted: null
created_at: null
description: null
id: null
input: "{}"
name: "keystone.services_list"
output: "{"result": [{"name": "ceilometer", "links": {"self": 
"enabled": true, "manager": {"client": "?"}, "_info": {"name": 
"ceilometer", "links": {"self": 
"enabled": true, "type": "metering", "id": 
"0a8e77a9a4d34eb3957ffb2a155c05b8", "description": "Openstack Metering 
Service"}, "_loaded": true, "type": "metering", "id": 
"0a8e77a9a4d34eb3957ffb2a155c05b8", "description": "Openstack Metering 
Service"}, {"name": "nova", "links": {"self": 
"enabled": true, "manager": {"client": "?"}, "_info": {"name": "nova", 
"links": {"self": "}"
state: null
state_info: null
tags: null
task_execution_id: null
updated_at: null
workflow_name: null

You can see that the output includes the action result. This happens all 
in single request - response manner. Exactly what we need.

-- Jirka

>>   The Mistral workflow needs to notify
>> (e.g. via Zaqar) or get polled for a result of the Workflow
>> execution.
>> Important fact is, that the actions which does not involve multiple
>> steps, should be a direct calls to the respective OpenStack APIs such
>> as
>> Heat, Ironic etc.
>> but in real life it is not like that. As an example we currently need
>> to
>> use heatclient instead of calling Heat API directly in some cases
>> because the client includes some business logic which we can't do
>> without.
>> So to solve this we either use Mistral API and deal with the
>> inconvenience that everything is a workflow or we'll use TripleO API
>> for
>> such cases but we'll need to deal with the fact that most of that
>> functionality will go away as OpenStack services evolve. This is
>> going
>> to cause the TripleO API to be unstable and I am not sure of we can
>> do
>> anything about it as it is the nature of the project.
>> Another fact is that such actions seem to be required only by GUI as
>> the
>> CLI commands are usually workflows. But it is essential that those
>> operations exist and are available via some API.
>> -- Jirka
>>>> This would also allow us to version the types of Mistral
>>>> environments
>>>> we create for use with workflows that support the various version
>>>> (should we choose to take it to this level).
>>>> Rather than focus on the environments mechanism I rather meant
>>>> this
>>>> prototype to be a sort of demonstration to show how we could call
>>>> a
>>>> workflow, how the code would cleanly move out of python-
>>>> tripleoclient
>>>> and into tripleo-common where it becomes a Mistral action, etc. I
>>>> needed the environment too... apologies for not taking the
>>>> example
>>>> further (I'm working as quickly as I can).
>>>> Be assured the code to create the environment could easily be
>>>> implemented as a workflow API call, where we have validations it
>>>> etc,
>>>> etc. and it can be called by a UI or CLI in an equally useful
>>>> fashion.
>>> Okay, so I initially thought we weren't making much progress on
>>> this
>>> discussion, but after some more thought and reading of the existing
>>> PoC,
>>> we're (maybe?) less far apart than I initially thought.
>>> I think there are kind of three different designs being discussed.
>>> 1) Rewrite a bunch of stuff into MistrYAML, with the idea that
>>> users
>>> could edit our workflows.  I think this is what I've been most
>>> strenuously objecting to, and for the most part my previous
>>> arguments
>>> pertain to this model.
>>> 2) However, I think there's another thing going on/planned with at
>>> least
>>> some of the actions.  It sounds like some of our workflows are
>>> going to
>>> essentially be a single action that just passes the REST params
>>> into our
>>> Python code.  This sort of API as a Service would be more palatable
>>> to
>>> me, as it doesn't really split our implementation between YAML and
>>> Python (the YAML is pretty much only defining the REST API in this
>>> model), but it still gives us a quick and easy REST interface to
>>> the
>>> existing code.  It also keeps a certain amount of separation
>>> between
>>> Mistral and the TripleO code in case we decide some day that we
>>> need a
>>> proper API service and need to swap out the Mistral frontend for a
>>> different one.  This should also be the easiest to implement since
>>> it
>>> doesn't involve rewriting anything - we're mostly just moving the
>>> existing code into Mistral actions and creating some pretty trivial
>>> Mistral workflows.
>>> 3) The thing I _want_ to see, which is a regular Python-based API
>>> service.  Again, you can kind of see my arguments around why I
>>> think we
>>> should do this elsewhere in the thread.  It's also worth noting
>>> that
>>> there is already an initial implementation of this proposed to
>>> tripleo-common, so it's not like we'd be starting from zero here
>>> either.
>>> I'm still not crazy about 2, but if it lets me stop spending
>>> excessive
>>> amounts of time on this topic it might be worth it. :-)
>>>>> As I said, this is a really fundamental part of the argument
>>>>> for
>>>>> creating a REST API for TripleO.  A huge reason Tuskar UI
>>>>> didn't work
>>>>> was that it had to reimplement all of the logic in
>>>>> tripleoclient.  Two
>>>>> parallel implementations in different languages is not a
>>>>> sustainable
>>>>> model of development, and on top of that developers will always
>>>>> focus
>>>>> on
>>>>> the CLI, which can do a lot of things the UI can't.  That was
>>>>> the
>>>>> straw
>>>>> that broke Tuskar UI's back in the end - new features like
>>>>> network
>>>>> isolation and Ceph were designed for the CLI, and had
>>>>> requirements
>>>>> the
>>>>> UI simply couldn't meet in a sane fashion.
>>>> And that is the fundamental part of this for me as well. If you
>>>> look
>>>> closely at my example you'll notice that I'm using an API for
>>>> everything (ignore the environment part for now please because as
>>>> I
>>>> explained above the latest feedback is we'd rather use a workflow
>>>> to
>>>> create that...). In my example python-tripleoclient calls the
>>>> workflow
>>>> using the same API that we would also consume via a UI. Contrast
>>>> this
>>>> with what we are actually implementing in tripleo-common today,
>>>> which
>>>> is we are initially calling the tripleo-common Python library
>>>> directly.
>>>> I think the end goal is that we wouldn't do this, but we are for
>>>> now...
>>>> so I would argue that actually in this regard my Mistral demo is
>>>> a step
>>>> ahead, not behind where we want to be here.
>>>>> It's not like we undertook the task of writing an API
>>>>> lightly.  In
>>>>> fact,
>>>>> I initially argued against it myself, but after talking to the
>>>>> GUI
>>>>> folks
>>>>> it was explained that just sticking all of our code in a Python
>>>>> library
>>>>> doesn't actually solve their problems.  They need something
>>>>> they can
>>>>> talk to (read: a REST API) that can handle the business
>>>>> logic.  This
>>>>> is
>>>>> the problem the TripleO API was designed to solve, not simply
>>>>> the
>>>>> task
>>>>> of running some pre-defined OpenStack API calls.  Which is why
>>>>> one of
>>>>> my
>>>>> first points was "is not a workflow API".
>>>> Ben, I am working with UI developers. I'm listening to their
>>>> needs and
>>>> developing API driven workflows to do the required steps for
>>>> deploying
>>>> via a UI. I'm trying to prototype and demonstrate how quickly and
>>>> easily it would be to wire those workflows up in such a manner
>>>> that we
>>>> can use them from python-tripleoclient and/or any UI at the same
>>>> time,
>>>> all via a generic stable workflow API. I would argue that it has
>>>> been a
>>>> success.
>>>> The hard question being asked of TripleO now (in particular
>>>> TripleO
>>>> cores) is given all this do we still want to go off and build our
>>>> own
>>>> API. And if we do what if any value do we get from it vs. a
>>>> solution
>>>> like Mistral?
>>>> Dan
>>>>> I realize I've now typed enough that everyone probably tuned
>>>>> out a
>>>>> few
>>>>> paragraphs ago, but I hope somewhere in that wall of text I've
>>>>> explained
>>>>> what I see as a disconnect between this proposal and what the
>>>>> TripleO
>>>>> API actually is.  There's a whole bunch more discussion that
>>>>> needs to
>>>>> happen beyond this, but I think until we're on the same page
>>>>> regarding
>>>>> the intent of the API we're not going to make meaningful
>>>>> progress
>>>>> here.
>>>>>>> 3) It ties us 100% to a given implementation.  If Mistral
>>>>>>> proves
>>>>>>> to
>>>>>>> be a
>>>>>>> poor choice for some reason, or insufficient for a
>>>>>>> particular use
>>>>>>> case,
>>>>>>> we have no alternative.  If we have an API and decide to
>>>>>>> change
>>>>>>> our
>>>>>>> implementation, nobody has to know or care.  This is kind
>>>>>>> of the
>>>>>>> whole
>>>>>>> point of having an API - it shields users from all the
>>>>>>> nasty
>>>>>>> implementation details under the surface.
>>>>>> Mistal's API is a generic workflow API. It is very much the
>>>>>> same
>>>>>> layer
>>>>>> that I think we would get if we were to integrate with
>>>>>> something
>>>>>> like
>>>>>> Ansible Tower... except that Mistral is part of OpenStack. It
>>>>>> integrates very nicely with OpenStack services and is very
>>>>>> customizable
>>>>>> with custom actions. The fact that Mistral sits much closer
>>>>>> to
>>>>>> OpenStack and is essentially a light shim on top of it is to
>>>>>> our
>>>>>> advantage (being TripleO). To think that we can build up a
>>>>>> proxy
>>>>>> API in
>>>>>> such a manner that we might be able to swap in an entirely
>>>>>> new
>>>>>> backend
>>>>>> (without even having a fully implement backend yet to begin
>>>>>> with)
>>>>>> is
>>>>>> for me a bit of a stretch. We've got a lot of "TripleO API"
>>>>>> maturing
>>>>>> before we'll get to this point. Which is why I lean towards
>>>>>> using a
>>>>>> generic workflow API to accomplis the same task.
>>>>>> I actually think rather than shielding users we should be
>>>>>> more
>>>>>> transparent about the actual workflows that are driving
>>>>>> deployment.
>>>>>> Smaller more focused workflows that we string together to
>>>>>> drive the
>>>>>> deployment.
>>>>>>> 4) It raises the bar even further for both new deployers
>>>>>>> and
>>>>>>> developers.
>>>>>>>    You already need to have a pretty firm grasp of Puppet
>>>>>>> and Heat
>>>>>>> templates to understand how our stuff works, not to mention
>>>>>>> a
>>>>>>> decent
>>>>>>> understanding of quite a number of OpenStack services.
>>>>>>> This presents a big chicken and egg problem for people new
>>>>>>> to
>>>>>>> OpenStack.
>>>>>>>    It's great that we're based on OpenStack and that allows
>>>>>>> people
>>>>>>> to
>>>>>>> peek
>>>>>>> under the hood and do some tinkering, but it can't be
>>>>>>> required
>>>>>>> for
>>>>>>> everyone.  A lot of our deployers are going to have little
>>>>>>> to no
>>>>>>> OpenStack experience, and TripleO is already a daunting
>>>>>>> task for
>>>>>>> those
>>>>>>> people (hell, it's daunting for people who _are_
>>>>>>> experienced).
>>>>>> And on the flipside you will get more of a community around
>>>>>> using
>>>>>> an
>>>>>> OpenStack project than you ever would going off and building
>>>>>> your
>>>>>> own
>>>>>> "Deployment/Workflow API".
>>>>>> I would actually argue this is less of a deployers thing and
>>>>>> more
>>>>>> of a
>>>>>> development tool choice. IMO most deployers will use python-
>>>>>> tripleoclient or some UI and not mistralclient directly. The
>>>>>> code
>>>>>> I've
>>>>>> posted this week shows a prototype of just this, Mistral is
>>>>>> swapped
>>>>>> in
>>>>>> such that you would never know it was involved because
>>>>>> python-
>>>>>> tripleoclient works like it always did. Deployers use our CLI
>>>>>> and
>>>>>> UI
>>>>>> tools like they always have, and developers gain a community
>>>>>> of
>>>>>> Mistral
>>>>>> developers (and documentation) which they can interact with
>>>>>> on
>>>>>> common
>>>>>> problems. Sounds like a win/win to me.
>>>>>>> 5) What does reimplementing all of our tested, well-
>>>>>>> understood
>>>>>>> Python
>>>>>>> into a new YAML format gain us?  This is maybe the biggest
>>>>>>> thing
>>>>>>> I'm
>>>>>>> missing from this whole discussion.  We lose a bunch of
>>>>>>> things
>>>>>>> (ease
>>>>>>> of
>>>>>>> transition from other Python projects, excellent existing
>>>>>>> testing
>>>>>>> framework, etc.), but what are we actually gaining other
>>>>>>> than the
>>>>>>> ability to say that we use N + 1 OpenStack
>>>>>>> services?  Because
>>>>>>> we're
>>>>>>> way
>>>>>>> past the point where "It's OpenStack deploying OpenStack"
>>>>>>> is
>>>>>>> sufficient
>>>>>>> reason for people to pay attention to us.  We need less
>>>>>>> "Ooh,
>>>>>>> neat"
>>>>>>> and
>>>>>>> more "Ooh, that's easy to use and works well."  It's still
>>>>>>> not
>>>>>>> clear
>>>>>>> to
>>>>>>> me that Mistral helps in any way with the latter.
>>>>>> Nobody suggested we reimplement everything. Much of the plan
>>>>>> to
>>>>>> move
>>>>>> code into tripleo-common would stay. Instead of building our
>>>>>> own
>>>>>> API
>>>>>> we'd just skip all that and focus on the code that is
>>>>>> actually
>>>>>> about
>>>>>> our deployments in the form of custom Mistral actions and
>>>>>> YAML
>>>>>> workflows.
>>>>>> The YAML workflows just ties together actions which are
>>>>>> actually
>>>>>> all
>>>>>> written in Python. YAML works quite well for this and is a
>>>>>> whole
>>>>>> lot
>>>>>> less verbose than writting everything we have in Python.
>>>>>> There is a
>>>>>> reason Heat, Ansible, and Mistral use YAML for these
>>>>>> things... and
>>>>>> I
>>>>>> think it works well. Understood you have an opinion on this,
>>>>>> but I
>>>>>> don't share the view that everything works better when
>>>>>> written in
>>>>>> Python. Take Puppet for example, we interface with that via
>>>>>> Hiera.
>>>>>> People will pay attention because we'll be able to add
>>>>>> features
>>>>>> faster.
>>>>>> By not having to build our own API and plumbing we can focus
>>>>>> on
>>>>>> actual
>>>>>> problems rather than boilerplate Python API code.
>>>>>>> 6) On the testing note, how do we test these workflows?  Do
>>>>>>> we
>>>>>>> know
>>>>>>> what
>>>>>>> happens when step X fails?  How do we test that they handle
>>>>>>> it
>>>>>>> properly
>>>>>>> in an automated and repeatable way?  In Python these are
>>>>>>> largely
>>>>>>> easy
>>>>>>> questions to answer: unit tests.  How do you unit test
>>>>>>> YAML?
>>>>>> The actions are all unit testable Python.
>>>>>> The workflows themselves would all get tested as part of our
>>>>>> CI.
>>>>>> With
>>>>>> Mistral workflows and the integration I'm proposing with both
>>>>>> the
>>>>>> CLI
>>>>>> and UI we'd have the same API driven workflows tested in both
>>>>>> cases. We
>>>>>> don't short circuit the API and call into a library like we
>>>>>> are
>>>>>> doing
>>>>>> today for tripleo-common.
>>>>>>>    This is a
>>>>>>> big reason I'm not even crazy about having Mistral on the
>>>>>>> back
>>>>>>> end of
>>>>>>> a
>>>>>>> TripleO API.  We'd be going from code that we can test and
>>>>>>> prove
>>>>>>> works
>>>>>>> in a variety of scenarios, to YAML that is tested and
>>>>>>> proven to
>>>>>>> work
>>>>>>> in
>>>>>>> exactly the three scenarios we run in CI.  This is
>>>>>>> basically the
>>>>>>> same
>>>>>>> situation we had with tripleo-incubator, and it was bad
>>>>>>> there
>>>>>>> too.
>>>>>>> I dunno.  Maybe I'm too late to this party to have any
>>>>>>> impact on
>>>>>>> the
>>>>>>> discussion, but I very much do not like the direction we're
>>>>>>> going
>>>>>>> and
>>>>>>> I
>>>>>>> would be remiss if I didn't at least point out my concerns
>>>>>>> with
>>>>>>> it.
>>>>>> You aren't late to the party. But I would encourage you to
>>>>>> look
>>>>>> closely
>>>>>> at the Mistral demos and examples that have been posted to
>>>>>> openstack-
>>>>>> dev before commenting further. Try them out, try Ansible
>>>>>> (tower),
>>>>>> try
>>>>>> Mistral, and then come back and have a hard look at what we
>>>>>> are
>>>>>> trying
>>>>>> to do by building our own TripleO API.
>>>>>> To me the crux of the problem isn't that we should expect
>>>>>> other
>>>>>> projects to build our APIs for us. Rather it is using the
>>>>>> right
>>>>>> tools
>>>>>> for the right jobs. TripleO has gotten off on the wrong path
>>>>>> a few
>>>>>> times. We tried to roll our own config manage tooling and
>>>>>> that
>>>>>> didn't
>>>>>> work out so well. I hate to see us go down the path of trying
>>>>>> to
>>>>>> write
>>>>>> our own deployment/workflow API when in fact we've already
>>>>>> got what
>>>>>> exactly what we need in OpenStack already. And a community
>>>>>> already
>>>>>> exists around it as well...
>>>>>> Dan
>>>>>>> -Ben
>>>>>>> On 01/13/2016 03:41 AM, Tzu-Mainn Chen wrote:
>>>>>>>> Hey all,
>>>>>>>> I realize now from the title of the other TripleO/Mistral
>>>>>>>> thread
>>>>>>>> [1] that
>>>>>>>> the discussion there may have gotten confused.  I think
>>>>>>>> using
>>>>>>>> Mistral for
>>>>>>>> TripleO processes that are obviously workflows - stack
>>>>>>>> deployment,
>>>>>>>> node
>>>>>>>> registration - makes perfect sense.  That thread is
>>>>>>>> exploring
>>>>>>>> practicalities
>>>>>>>> for doing that, and I think that's great work.
>>>>>>>> What I inappropriately started to address in that thread
>>>>>>>> was a
>>>>>>>> somewhat
>>>>>>>> orthogonal point that Dan asked in his original email,
>>>>>>>> namely:
>>>>>>>> "what it might look like if we were to use Mistral as a
>>>>>>>> replacement
>>>>>>>> for the
>>>>>>>> TripleO API entirely"
>>>>>>>> I'd like to create this thread to talk about that; more
>>>>>>>> of a
>>>>>>>> 'should we'
>>>>>>>> than 'can we'.  And to do that, I want to indulge in a
>>>>>>>> thought
>>>>>>>> exercise
>>>>>>>> stemming from an IRC discussion with Dan and
>>>>>>>> others.  All,
>>>>>>>> please
>>>>>>>> correct me
>>>>>>>> if I've misstated anything.
>>>>>>>> The IRC discussion revolved around one use case:
>>>>>>>> deploying a
>>>>>>>> Heat
>>>>>>>> stack
>>>>>>>> directly from a Swift container.  With an updated patch,
>>>>>>>> the
>>>>>>>> Heat
>>>>>>>> CLI can
>>>>>>>> support this functionality natively.  Then we don't need
>>>>>>>> a
>>>>>>>> TripleO
>>>>>>>> API; we
>>>>>>>> can use Mistral to access that functionality, and we're
>>>>>>>> done,
>>>>>>>> with
>>>>>>>> no need
>>>>>>>> for additional code within TripleO.  And, as I understand
>>>>>>>> it,
>>>>>>>> that's the
>>>>>>>> true motivation for using Mistral instead of a TripleO
>>>>>>>> API:
>>>>>>>> avoiding custom
>>>>>>>> code within TripleO.
>>>>>>>> That's definitely a worthy goal... except from my
>>>>>>>> perspective,
>>>>>>>> the
>>>>>>>> story
>>>>>>>> doesn't quite end there.  A GUI needs additional
>>>>>>>> functionality,
>>>>>>>> which boils
>>>>>>>> down to: understanding the Heat deployment templates in
>>>>>>>> order
>>>>>>>> to
>>>>>>>> provide
>>>>>>>> options for a user; and persisting those options within a
>>>>>>>> Heat
>>>>>>>> environment
>>>>>>>> file.
>>>>>>>> Right away I think we hit a problem.  Where does the code
>>>>>>>> for
>>>>>>>> 'understanding
>>>>>>>> options' go?  Much of that understanding comes from the
>>>>>>>> capabilities map
>>>>>>>> in tripleo-heat-templates [2]; it would make sense to me
>>>>>>>> that
>>>>>>>> responsibility
>>>>>>>> for that would fall to a TripleO library.
>>>>>>>> Still, perhaps we can limit the amount of TripleO
>>>>>>>> code.  So to
>>>>>>>> give
>>>>>>>> API
>>>>>>>> access to 'getDeploymentOptions', we can create a Mistral
>>>>>>>> workflow.
>>>>>>>>     Retrieve Heat templates from Swift -> Parse
>>>>>>>> capabilities map
>>>>>>>> Which is fine-ish, except from an architectural
>>>>>>>> perspective
>>>>>>>> 'getDeploymentOptions' violates the abstraction layer
>>>>>>>> between
>>>>>>>> storage and
>>>>>>>> business logic, a problem that is compounded because
>>>>>>>> 'getDeploymentOptions'
>>>>>>>> is not the only functionality that accesses the Heat
>>>>>>>> templates
>>>>>>>> and
>>>>>>>> needs
>>>>>>>> exposure through an API.  And, as has been discussed on a
>>>>>>>> separate
>>>>>>>> TripleO
>>>>>>>> thread, we're not even sure Swift is sufficient for our
>>>>>>>> needs;
>>>>>>>> one
>>>>>>>> possible
>>>>>>>> consideration right now is allowing deployment from
>>>>>>>> templates
>>>>>>>> stored in
>>>>>>>> multiple places, such as the file system or git.
>>>>>>>> Are we going to have duplicate 'getDeploymentOptions'
>>>>>>>> workflows
>>>>>>>> for
>>>>>>>> each
>>>>>>>> storage mechanism?  If we consolidate the storage code
>>>>>>>> within a
>>>>>>>> TripleO
>>>>>>>> library, do we really need a *workflow* to call a single
>>>>>>>> function?  Is a
>>>>>>>> thin TripleO API that contains no additional business
>>>>>>>> logic
>>>>>>>> really
>>>>>>>> so bad
>>>>>>>> at that point?
>>>>>>>> My gut reaction is to say that proposing Mistral in place
>>>>>>>> of a
>>>>>>>> TripleO API
>>>>>>>> is to look at the engineering concerns from the wrong
>>>>>>>> direction.  The
>>>>>>>> Mistral alternative comes from a desire to limit custom
>>>>>>>> TripleO
>>>>>>>> code at all
>>>>>>>> costs.  I think that is an extremely dangerous attitude
>>>>>>>> that
>>>>>>>> leads
>>>>>>>> to
>>>>>>>> compromises and workarounds that will quickly lead to a
>>>>>>>> shaky
>>>>>>>> code
>>>>>>>> base
>>>>>>>> full of design flaws that make it difficult to implement
>>>>>>>> or
>>>>>>>> extend
>>>>>>>> any
>>>>>>>> functionality cleanly.
>>>>>>>> I think the correct attitude is to simply look at the
>>>>>>>> problem
>>>>>>>> we're
>>>>>>>> trying to solve and find the correct architecture.  For
>>>>>>>> these
>>>>>>>> get/set
>>>>>>>> methods that the API needs, it's pretty simple: storage
>>>>>>>> -> some
>>>>>>>> logic ->
>>>>>>>> a REST API.  Adding a workflow engine on top of that is
>>>>>>>> unneeded,
>>>>>>>> and I
>>>>>>>> believe that means it's an incorrect solution.
>>>>>>>> Thanks,
>>>>>>>> Tzu-Mainn Chen
>>>>>>>> [1] http://lists.openstack.org/pipermail/openstack-dev/20
>>>>>>>> 16-Jan
>>>>>>>> uary
>>>>>>>> /083757.html
>>>>>>>> [2] https://github.com/openstack/tripleo-heat-templates/b
>>>>>>>> lob/ma
>>>>>>>> ster
>>>>>>>> /capabilities_map.yaml
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>>>>>>>> ev
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