Open Stack

> On Wed, 2016-01-27 at 09:36 -0500, 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/77ffd2
> > > > > > fa
> > > > > > 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
> > > (GUI/CLI
> > >  > 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
> > 
> > 
> > >  The Mistral workflow needs to notify
> > > (e.g. via Zaqar) or get polled for a result of the Workflow
> > > execution.
> 
> I think I misread your request here. For now polling is required. I'd
> just create a common Python and/or Javascript function to do this for
> python-tripleoclient and the UI. That way you can call a workflow and
> wait on the result in a synchronous manner if you want a convenient way
> to do it.
>

Just a quick observation: a Python function is unusable by non-Python
GUIs, and client-side Javascript is unusable by the CLI and would require
duplicated code across GUIs, so I don't think either solution is ideal.

> 
> Lets do proceed with looking at Zaqar integration and see if that
> helps. That seems like the best long term solution. I don't think it
> would be very hard to integrate with Zaqar within our workflows...
> 

If we go the Mistral route, then this sounds like the only good
solution.


Mainn

>
> Dan
> 
> 
> > > 
> > > 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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> > > > > > > > > tack-d
> > > > > > > > > ev
> > > > > > > > > 
> > > > > > > > 
> > > > > > > > _________________________________________________________
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