On 18.1.2016 19:49, Tzu-Mainn Chen wrote:
----- Original Message -----On Thu, 2016-01-14 at 16:04 -0500, Tzu-Mainn Chen wrote:----- Original Message -----On Wed, Jan 13, 2016 at 04:41:28AM -0500, 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.Actually, that whole capabilities map thing is a workaround for a missing feature in Heat, which I have proposed, but am having a hard time reaching consensus on within the Heat community: https://review.openstack.org/#/c/196656/ Given that is a large part of what's anticipated to be provided by the proposed TripleO API, I'd welcome feedback and collaboration so we can move that forward, vs solving only for TripleO.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?Actually, this is an argument for making the validation part of the deployment a workflow - then the interface with the storage mechanism becomes more easily pluggable vs baked into an opaque-to-operators API. E.g, in the long term, imagine the capabilities feature exists in Heat, you then have a pre-deployment workflow that looks something like: 1. Retrieve golden templates from a template store 2. Pass templates to Heat, get capabilities map which defines features user must/may select. 3. Prompt user for input to select required capabilites 4. Pass user input to Heat, validate the configuration, get a mapping of required options for the selected capabilities (nested validation) 5. Push the validated pieces ("plan" in TripleO API terminology) to a template store This is a pre-deployment validation workflow, and it's a superset of the getDeploymentOptions feature you refer to. Historically, TripleO has had a major gap wrt workflow, meaning that we've always implemented it either via shell scripts (tripleo-incubator) or python code (tripleo-common/tripleo-client, potentially TripleO API). So I think what Dan is exploring is, how do we avoid reimplementing a workflow engine, when a project exists which already does that.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 it's not about limiting TripleO code at all costs, it's about learning from past mistakes, where long-term TripleO specific workarounds for gaps in other projects have become serious technical debt. For example, the old merge.py approach to template composition was a workaround for missing heat features, then Tuskar was another workaround (arguably) for missing heat features, and now we're again proposing a long-term workaround for some missing heat features, some of which are already proposed (referring to the API for capabilities resolution).This is an important point, thanks for bringing it up! I think that I might have a different understanding of the lessons to be learned from Tuskar's limitations. There were actually two issues that arose. The first was that Tuskar was far too specific in how it tried to manipulated Heat pieces. The second - and more serious, from my point of view - was that there literally was no way for an API-based GUI to perform the tasks it needed to in order to do the correct manipulation (environment selection), because there was no Heat API in place for doing so. My takeaway from the first issue was that any potential TripleO API in the future needed to be very low-level, a light skimming on top of the OpenStack services it uses. The plan creation process that the tripleo-common library spec describes is that: it's just a couple of methods designed to allow a user to create an environment file, which can then be used for deploying the overcloud. My takeaway from the second issue was a bit more complicated. A required feature was missing, and although the proper functionality needed to enable it in Heat was identified, it was unclear (and remains unclear) whether that feature truly belonged in Heat. What does a GUI do then? The GUI could take a cycle off, which is essentially what happened here; I don't think that's a reasonable solution. We could hope that we arrive at a 100% foolproof and immutable deployment solution in the future, arriving at a point where no new features would ever be needed; I don't think that's a practical hope. The third solution that came to mind was the idea of creating the TripleO API. It gives us a place to add in missing features if needed. And I think it also gives us a useful layer of indirection. The consumers of TripleO want a stable API, so that a new release doesn't force them to do a massive update of their code; the TripleO API would provide that, allowing us to switch code behind the scenes (say, if the capabilities feature lands in Heat).I think the above example would work equally well in a generic workflow sort of tool. You could image that the inputs to the workflow remain the same... but rather than running our own code in some interim step we simply call Heat directly for the capabilities map feature. So regardless of whether we build our own API or use a generic workflow too I think we still have what I would call a "release valve" to let us inject some custom code (actions) into the workflow. Like we discussed last week on IRC I would like to minimize the number of custom actions we have (with an eye towards things living in the upstream OpenStack projects) but it is fine to do this either way and would work equally well w/ Mistral and TripleO API.I think I kinda view TripleO as a 'best practices' project. Using OpenStack is a confusing experience, with a million different options and choices to make. TripleO provides users with an excellent guide. But the problem is that best practices change, and I think that perceived instability is dangerous for adoption of TripleO. So having a TripleO library and its associated API be a 'best practices' library makes sense to me. It gives consumers a stable platform upon which to use TripleO, while allowing us to be flexible behind the scenes. The 'best practice' for Heat capabilities right now is a workaround, because it hasn't been judged to be suitable to go into Heat itself. If that changes, we get to shift as well - and all of these changes are invisible to the API consumer.I mentioned this in my "Driving workflows with Mistral" thread but with regards to stability I view say Heat's v1 API or Mistral's v2 API as both being way more stable that what we could ever achieve with TripleO API. The real trick to API stability with something like Heat or Mistral is how we manage the inputs and outputs to Stacks and Workflows themselves. So long as we are mindful of this I can't image an end user (say a GUI writer or whoever) would really care whether they POST to Mistral or something we've created. The nice thing about using other OpenStack projects like Heat or Mistral is that they very likely have better community and documentation around these things as well that we would ever have. The more I look at using Mistral for some of the cases that have been brought up the more it seems to make sense for a lot of the workflows we need. I don't believe we can achieve better stability by creating what sounds more and more like a shim/proxy API rather than using the versioned API's that OpenStack already provides. There may be some corner cases where a "GUI helper" API comes into play for some sort of caching or something. I'm not blocking anyone from creating these sorts of features if they need them. And again if it is something that could be added to an upstream OpenStack project like Heat or Mistral I would look there first. So perhaps Zaqar for websockets instead of rolling our own, this sort of thing. What does concern me is that we are overstating what TripleO API should actually contain should we choose to pursue it. Initially it was positioned as the "TripleO workflow API". I think we now agree that we probably shouldn't put all of our workflows behind it. So if our stance has changed would it make sense to compile a new list of what we believe belongs behind our own TripleO API vs. what we consider workflows.I wonder if it would be helpful to get operator feedback here - show them the advantages/disadvantages of both options and to get a sense of what might be useful/necessary for them to use TripleO effectively?
(I'm going off on a tangent a bit, but please bear with me, i'm using all that to support the point in the end. The implications of building a TripleO API touch on various topics.)
Yes i think we should gather operator feedback. We already got some, but we should gather more whenever possible.
One kind of (negative) feedback i've heard is that overcloud management is too much of a "blackbox" compared to what operators are used to. The feedback i recall was that it's hard to tell what is going to happen when running an overcloud stack update, and that we cannot re-execute the software config management independently.
Building another umbrella API to rule the already largely umbrella-like deployment process (think what all responsibilities lie within the tripleo-heat-templates codebase, and within the single 'overcloud' Heat stack) would probably make matters more blackboxy and go further in the direction of "i feel like i don't know what's happening to my cloud when i use the management tool".
What i think could improve the situation for operators is trying to chunk up what we already have into smaller, more independently operable parts. The split-stack approach already discussed on the TripleO meeting and on #tripleo could help with this. Essentially separating our hardware management from our software config management. Being able to re-apply software configuration without being afraid of having nodes accidentally re-provisioned from scratch.
In general i think TripleO could be a little more "UNIXy" - composed of smaller parts that make sense on their own, transparent to the operator, more modular and modifiable, and in effect more receptive of how varying are the real world deployment environments (various Neutron and Cinder plugins, Keystone backends, composable set of services, custom node types etc.).
Workflow persisted in a data-like fashion is probably more modifiable by the operator than Python code of a REST API. We've seen hard assumptions cause problems in the past. (Think the unoverridable CLI parameters issue we used to have, and how we had to move to a model of "CLI provides its values, but you can always override them or provide additional ones with an environment file if needed", which we now use extensively). I'm a bit concerned that building a new REST API on top of everything would impose new rigid assumptions that could cause more harm than good in the end. I'm concerned that it would be usable only for very basic deployments, while the world of real deployments has its own pace and requirements not fitting the "best practices" as defined by the API, having to bypass the API far too often and slowly pushing it into abandonment over time.
My mind is probably biased towards the the operator feedback that resonated with me the most, i've heard pro-blackbox opinions too (though not from operators yet IIRC). So take what i wrote just as my 2 cents, but i think it's necessary to consider the above issues when thinking about the implications of building a TripleO API.
Regarding the non-workflow kind of features we need for empowering GUI, wouldn't those be useful for normal (tenant) Heat stack deployments in the overcloud too? It sounds to me that features like "driving a Heat stack deployment with the same powers from CLI or GUI", "updating a CLI-created stack from GUI and vice versa", "understanding/parsing what are the configuration options of my Heat templates" are all features that are not specific to TripleO, and could be useful for tenant Heat stacks too. So perhaps these should be implemented in Heat? If that can't happen fast enough, then we might need to put some workarounds in place for now, but it might be better if we didn't advertise those as a stable solution.
Jirka
MainnDanMainnI 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.What may help is if we can work through the proposed API spec, and identify which calls can reasonably be considered workflows vs those where it's really just proxying an API call with some logic? When we have a defined list of "not workflow" API requirements, it'll probably be much easier to rationalize over the value of a bespoke API vs mistral? Steve ___________________________________________________________________ _______ OpenStack Development Mailing List (not for usage questions) Unsubscribe: openstack-dev-requ...@lists.openstack.org?subject:unsu bscribe http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev_____________________________________________________________________ _____ OpenStack Development Mailing List (not for usage questions) Unsubscribe: openstack-dev-requ...@lists.openstack.org?subject:unsubs cribe http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev__________________________________________________________________________ OpenStack Development Mailing List (not for usage questions) Unsubscribe: openstack-dev-requ...@lists.openstack.org?subject:unsubscribe http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev__________________________________________________________________________ OpenStack Development Mailing List (not for usage questions) Unsubscribe: openstack-dev-requ...@lists.openstack.org?subject:unsubscribe http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
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