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

Ryan Brady rbrady at redhat.com
Fri Jan 22 18:30:44 UTC 2016

On Fri, Jan 22, 2016 at 12:24 PM, Ben Nemec <openstack at nemebean.com> 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.
The UI for is the CLI or the GUI right?  The typical method for interacting
with TripleO seems defined that way.  If we're worried about it being
friendly enough to integrate with I'm sure it could be easily explained in
a doc.  Underneath the difference is calling to :8989/v2/executions instead
of :8585/v1/deploy.  I'm not convinced there's a large enough difference
here to say that one is more user-friendly or not than the other.

> 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.
> 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.
> 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.

And an additional 14 or so active projects TripleO created, right?

> 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).

The original vision statement [1] for TripleO has not changed in some
time.  "TripleO is a program aimed at installing, upgrading and operating
OpenStack clouds using OpenStack's own cloud facilities as the
foundations".  I'm not disagreeing that TripleO *could* be a deployment
API, but that's not the language used in the wiki and if the goal is an API
then maybe this needs to be formalized to get everyone in the project on
the same page.  Following along with the statement as it stands, using
existing OpenStack services sounds like a mandate.  How do we decide as a
project when something within OpenStack can be improved or when we just
create something new?  How do we convey that justification to both
developers and users?

> 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.

So workflows are in yaml, but the actions are still in python.  The actions
have an __init__ and a run method which looks testable to me.

> 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.
> 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?  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.
If a workflow is composed of one or more actions, is it enough to test the
actions?  When I compare that to how we test now I think it does.

> 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.
> -Ben
I don't think you're late here at all.  I think more folks should weigh in
so we can get to the bottom of this.

- Ryan

[1] https://wiki.openstack.org/wiki/TripleO

> 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
> > 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/2016-January/083757.html
> > [2]
> https://github.com/openstack/tripleo-heat-templates/blob/master/capabilities_map.yaml
> >
> >
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Ryan Brady
Cloud Engineering
rbrady at redhat.com
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