Disclaimer: I swear I'll stop posting this sort of thing soon, but I'm
new to the project. I only mention it again because it's relevant in
that I missed any of the discussion on why proxying from tuskar API to
other APIs is looked down upon. Jiri and I had been talking yesterday
and he mentioned it to me when I started to ask these same sorts of
questions.
On 12/11/2013 07:33 AM, Jiří Stránský wrote:
Hi all,
TL;DR: I believe that "As an infrastructure administrator, Anna
wants a
CLI for managing the deployment providing the same fundamental
features
as UI." With the planned architecture changes (making tuskar-api
thinner
and getting rid of proxying to other services), there's not an obvious
way to achieve that. We need to figure this out. I present a few
options
and look forward for feedback.
Previously, we had planned Tuskar arcitecture like this:
tuskar-ui <-> tuskarclient <-> tuskar-api <-> heat-api|ironic-api|etc.
My biggest concern was that having each client call out to the
individual APIs directly put a lot of knowledge into the clients that
had to be replicated across clients. At the best case, that's simply
knowing where to look for data. But I suspect it's bigger than that
and there are workflows that will be implemented for tuskar needs. If
the tuskar API can't call out to other APIs, that workflow
implementation needs to be done at a higher layer, which means in each
client.
Something I'm going to talk about later in this e-mail but I'll
mention here so that the diagrams sit side-by-side is the potential
for a facade layer that hides away the multiple APIs. Lemme see if I
can do this in ASCII:
tuskar-ui -+ +-tuskar-api
| |
+-client-facade-+-nova-api
| |
tuskar-cli-+ +-heat-api
The facade layer runs client-side and contains the business logic that
calls across APIs and adds in the tuskar magic. That keeps the tuskar
API from calling into other APIs* but keeps all of the API call logic
abstracted away from the UX pieces.
* Again, I'm not 100% up to speed with the API discussion, so I'm
going off the assumption that we want to avoid API to API calls. If
that isn't as strict of a design principle as I'm understanding it to
be, then the above picture probably looks kinda silly, so keep in mind
the context I'm going from.
For completeness, my gut reaction was expecting to see something like:
tuskar-ui -+
|
+-tuskar-api-+-nova-api
| |
tuskar-cli-+ +-heat-api
Where a tuskar client talked to the tuskar API to do tuskar things.
Whatever was needed to do anything tuskar-y was hidden away behind the
tuskar API.
This meant that the "integration logic" of how to use heat, ironic and
other services to manage an OpenStack deployment lied within
*tuskar-api*. This gave us an easy way towards having a CLI - just
build
tuskarclient to wrap abilities of tuskar-api.
Nowadays we talk about using heat and ironic (and neutron? nova?
ceilometer?) apis directly from the UI, similarly as Dashboard does.
But our approach cannot be exactly the same as in Dashboard's case.
Dashboard is quite a thin wrapper on top of python-...clients, which
means there's a natural parity between what the Dashboard and the CLIs
can do.
When you say python- clients, is there a distinction between the CLI
and a bindings library that invokes the server-side APIs? In other
words, the CLI is packaged as CLI+bindings and the UI as GUI+bindings?
We're not wrapping the APIs directly (if wrapping them directly
would be
sufficient, we could just use Dashboard and not build Tuskar API at
all). We're building a separate UI because we need *additional
logic* on
top of the APIs. E.g. instead of directly working with Heat templates
and Heat stacks to deploy overcloud, user will get to pick how many
control/compute/etc. nodes he wants to have, and we'll take care of
Heat
things behind the scenes. This makes Tuskar UI significantly thicker
than Dashboard is, and the natural parity between CLI and UI vanishes.
By having this logic in UI, we're effectively preventing its use from
CLI. (If i were bold i'd also think about integrating Tuskar with
other
software which would be prevented too if we keep the business logic in
UI, but i'm not absolutely positive about use cases here).
I see your point about preventing its use from the CLI, but more
disconcerting IMO is that it just doesn't belong in the UI. That sort
of logic, the "Heat things behind the scenes", sounds like the
jurisdiction of the API (if I'm reading into what that entails
correctly).
Now this raises a question - how do we get CLI reasonably on par with
abilities of the UI? (Or am i wrong that Anna the infrastructure
administrator would want that?)
To reiterate my point above, I see the idea of getting the CLI on par,
but I also see it as striving for a cleaner design as well.
Here are some options i see:
1) Make a thicker python-tuskarclient and put the business logic
there.
Make it consume other python-*clients. (This is an unusual approach
though, i'm not aware of any python-*client that would consume and
integrate other python-*clients.)
-1 in favor of #3 below (spoiler: I'm -1 to that too, I suppose this
is a -2)
2) Make a thicker tuskar-api and put the business logic there.
(This is
the original approach with consuming other services from
tuskar-api. The
feedback on this approach was mostly negative though.)
A tentative +1. Tentative until I dig up the feedback on intra-API
calls and see why it was negative, in which case I may buy into those
arguments too.
3) Keep tuskar-api and python-tuskarclient thin, make another library
sitting between Tuskar UI and all python-***clients. This new project
would contain the logic of using undercloud services to provide the
"tuskar experience" it would expose python bindings for Tuskar UI and
contain a CLI. (Think of it like traditional python-*client but
instead
of consuming a REST API, it would consume other python-*clients. I
wonder if this is overengineering. We might end up with too many
projects doing too few things? :) )
This is the sort of thing I was describing with the facade image
above. Rather than beefing up python-tuskarclient, I'd rather we have
a specific logic layer that isn't the CLI nor is it the bindings, but
is specifically for the purposes of coordination across multiple APIs.
That said, I'm -1 to my own facade diagram. I think that should live
service-side in the API.
4) Keep python-tuskarclient thin, but build a separate CLI app that
would provide same integration features as Tuskar UI does. (This would
lead to code duplication. Depends on the actual amount of logic to
duplicate if this is bearable or not.)
I don't know the level of logic duplication that would happen, but the
design feels wrong from the start.
Which of the options you see as best? Did i miss some better
option? Am
i just being crazy and trying to solve a non-issue? Please tell me :)
I'm not saying you're not crazy. I'm saying you're not alone in being
crazy if you are :)
Please don't consider the time aspect of this, focus rather on what's
the right approach, where we want to get eventually. (We might want to
keep a thick Tuskar UI for Icehouse not to set the hell loose, there
will be enough refactoring already.)
Thanks
Jirka
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