Re: [openstack-dev] [horizon] REST and Django

Wed, 10 Dec 2014 10:43:06 -0800


I think we're arguing for the same thing, but maybe slightly different approach. I think we can both agree that a middle-layer is required, whether we intend to use it as a proxy or REST endpoints. Regardless of the approach, the client needs to relay what API it wants to invoke, and you can do that either via RPC or REST. I personally prefer the REST approach because it shields the client. Client just needs to know which URL to hit in order to invoke a certain API, and does not need to know the procedure name or parameters ordering. Having said all of that, I do believe we should keep it as thin as possible. I do like the idea of having separate classes for different API versions. What we have today is a thin REST layer that acts like a proxy. You hit a certain URL, and the middle layer forwards the API invokation. The only exception to this rule is support for batch deletions.

-----Tihomir Trifonov <t.trifo...@gmail.com> wrote: -----
To: "OpenStack Development Mailing List (not for usage questions)" <openstack-dev@lists.openstack.org>
From: Tihomir Trifonov <t.trifo...@gmail.com>
Date: 12/10/2014 03:04AM
Subject: Re: [openstack-dev] [horizon] REST and Django

Richard, thanks for the reply,


I agree that the given example is not a real REST. But we already have the REST API - that's Keystone, Nova, Cinder, Glance, Neutron etc, APIs. So what we plan to do here? To add a new REST layer to communicate with other REST API? Do we really need Frontend-REST-REST architecture ? My opinion is that we don't need another REST layer as we currently are trying to go away from the Django layer, which is the same - another processing layer. Although we call it REST proxy or whatever - it doesn't need to be a real REST, but just an aggregation proxy that combines and forwards some requests with adding minimal processing overhead. What makes sense for me is to keep the authentication in this layer as it is now - push a cookie to the frontend, but the REST layer will extract the auth tokens from the session storage and prepare the auth context for the REST API request to OS services. This way we will not expose the tokens to the JS frontend, and will have strict control over the authentication. The frontend will just send data requests, they will be wrapped with auth context and forwarded.

Regarding the existing issues with versions in the API - for me the existing approach is wrong. All these fixes were made as workarounds. What should have been done is to create abstractions for each version and to use a separate class for each version. This was partially done for the keystoneclient in api/keystone.py, but not for the forms/views, where we still have if-else for versions. What I suggest here is to have different(concrete) views/forms for each version, and to use them according the context. If the Keystone backend is v2.0 - then in the Frontend use keystone2() object, otherwise use keystone3() object. This of course needs some more coding, but is much cleaner in terms of customization and testing. For me the current hacks with 'if keystone.version == 3.0' are wrong at many levels. And this can be solved now. The problem till now was that we had one frontend that had to be backed by different versions of backend components. Now we can have different frontends that map to specific backend. That's how I understand the power of Angular with it's views and directives. That's where I see the real benefit of using full-featured frontend. Also imagine how easy will be then to deprecate a component version, compared to what we need to do now for the same.

Otherwise we just rewrite the current Django middleware with another DjangoRest middleware and don't change anything, we don't fix the problems. We just move them to another place.

I still think that in Paris we talked about a new generation of the Dashboard, a different approach on building the frontend for OpenStack. What I've heard there from users/operators of Horizon was that it was extremely hard to add customizations and new features to the Dashboard, as all these needed to go through upstream changes and to wait until next release cycle to get them. Do we still want to address these concerns and how? Please, correct me if I got things wrong.


On Wed, Dec 10, 2014 at 11:56 AM, Richard Jones <r1chardj0...@gmail.com> wrote:
Sorry I didn't respond to this earlier today, I had intended to.

What you're describing isn't REST, and the principles of REST are what have been guiding the design of the new API so far. I see a lot of value in using REST approaches, mostly around clarity of the interface.

While the idea of a very thin proxy seemed like a great idea at one point, my conversations at the summit convinced me that there was value in both using the client interfaces present in the openstack_dashboard/api code base (since they abstract away many issues in the apis including across versions) and also value in us being able to clean up (for example, using "project_id" rather than "project" in the user API we've already implemented) and extend those interfaces (to allow batched operations).

We want to be careful about what we expose in Horizon to the JS clients through this API. That necessitates some amount of code in Horizon. About half of the current API for keysone represents that control (the other half is docstrings :)


     Richard


On Tue Dec 09 2014 at 9:37:47 PM Tihomir Trifonov <t.trifo...@gmail.com> wrote:
Sorry for the late reply, just few thoughts on the matter.

IMO the REST middleware should be as thin as possible. And I mean thin in terms of processing - it should not do pre/post processing of the requests, but just unpack/pack. So here is an example:

instead of making AJAX calls that contain instructions:

​​
POST --json --data {"action": "delete", "data": [ {"name": "item1"}, {"name": "item2"}, {"name": "item3" ]}

I think a better approach is just to pack/unpack batch commands, and leave execution to the frontend/backend and not middleware:


​​
POST --json --data {"
​batch
":
​[ 
{​
"
​
action"
​ : "delete"​
,
​"payload": ​
{"name": "item1"}
​, 
{​
"
​
action"
​ : "delete"​
,
​
"payload": 
​
{"name": "item
​2
"}
​, 
{​
"
​
action"
​ : "delete"​
,
​
"payload": 
​
{"name": "item
​3
"}
​ ] ​
​
​
}

​The idea is that the middleware should not know the actual data. It should ideally just unpack the data:

​​responses = []
 
for cmd in
​ ​
​
​
request.POST['batch']:​
   
​
​​responses
​.append(​
​
getattr(controller, cmd['action']
​)(**
cmd['​payload']
​)​)
 
​return responses​


​and the frontend(JS) will just send batches of simple commands, and will receive a list of responses for each command in the batch. The error handling will be done in the frontend​(JS) as well.
 
​

For the more complex example of 'put()' where we have dependent objects:

project = api.keystone.tenant_get(request, id)
kwargs = self._tenant_kwargs_from_DATA(request.DATA, enabled=None)
api.keystone.tenant_update(request, project, **kwargs)


In practice the project data should be already present in the frontend(assuming that we already loaded it to render the project form/view), so 

​
​
POST --json --data {"
​batch
": 
​[ 
{​
"
​
action"
​ : "tenant_update"​
, 
​"payload": ​
{"project": js_project_object.id, "name": "some name", "prop1": "some prop", "prop2": "other prop, etc."}
​
​ ] ​
​
​
}​

So in general we don't need to recreate the full state on each REST call, if we make the Frontent full-featured application. This way - the frontend will construct the object, will hold the cached value, and will just send the needed requests as single ones or in batches, will receive the response from the API backend, and will render the results. The whole processing logic will be held in the Frontend(JS), while the middleware will just act as proxy(un/packer). This way we will maintain just the logic in the frontend, and will not need to duplicate some logic in the middleware.


 

On Tue, Dec 2, 2014 at 4:45 PM, Adam Young <ayo...@redhat.com> wrote:
On 12/02/2014 12:39 AM, Richard Jones wrote:
On Mon Dec 01 2014 at 4:18:42 PM Thai Q Tran <tqt...@us.ibm.com> wrote:

I agree that keeping the API layer thin would be ideal. I should add that having discrete API calls would allow dynamic population of table. However, I will make a case where it might be necessary to add additional APIs. Consider that you want to delete 3 items in a given table.

If you do this on the client side, you would need to perform: n * (1 API request + 1 AJAX request)
If you have some logic on the server side that batch delete actions: n * (1 API request) + 1 AJAX request

Consider the following:
n = 1, client = 2 trips, server = 2 trips
n = 3, client = 6 trips, server = 4 trips
n = 10, client = 20 trips, server = 11 trips
n = 100, client = 200 trips, server 101 trips

As you can see, this does not scale very well.... something to consider...

 This is not something Horizon can fix.  Horizon can make matters worse, but cannot make things better.

If you want to delete 3 users,   Horizon still needs to make 3 distinct calls to Keystone.

To fix this, we need either batch calls or a standard way to do multiples of the same operation.

The unified API effort it the right place to drive this.







Yep, though in the above cases the client is still going to be hanging, waiting for those server-backend calls, with no feedback until it's all done. I would hope that the client-server call overhead is minimal, but I guess that's probably wishful thinking when in the land of random Internet users hitting some provider's Horizon :)

So yeah, having mulled it over myself I agree that it's useful to have batch operations implemented in the POST handler, the most common operation being DELETE.

Maybe one day we could transition to a batch call with user feedback using a websocket connection.


     Richard

Richard Jones ---11/27/2014 05:38:53 PM---On Fri Nov 28 2014 at 5:58:00 AM Tripp, Travis S <travis.tr...@hp.com> wrote:

From: Richard Jones <r1chardj0...@gmail.com>
To: "Tripp, Travis S" <travis.tr...@hp.com>, OpenStack List <openstack-dev@lists.openstack.org>
Date: 11/27/2014 05:38 PM
Subject: Re: [openstack-dev] [horizon] REST and Django




On Fri Nov 28 2014 at 5:58:00 AM Tripp, Travis S <travis.tr...@hp.com> wrote:

    Hi Richard,

    You are right, we should put this out on the main ML, so copying thread out to there.  ML: FYI that this started after some impromptu IRC discussions about a specific patch led into an impromptu google hangout discussion with all the people on the thread below.

Thanks Travis!

 
    As I mentioned in the review[1], Thai and I were mainly discussing the possible performance implications of network hops from client to horizon server and whether or not any aggregation should occur server side.   In other words, some views  require several APIs to be queried before any data can displayed and it would eliminate some extra network requests from client to server if some of the data was first collected on the server side across service APIs.  For example, the launch instance wizard will need to collect data from quite a few APIs before even the first step is displayed (I’ve listed those out in the blueprint [2]).

    The flip side to that (as you also pointed out) is that if we keep the API’s fine grained then the wizard will be able to optimize in one place the calls for data as it is needed. For example, the first step may only need half of the API calls. It also could lead to perceived performance increases just due to the wizard making a call for different data independently and displaying it as soon as it can.

Indeed, looking at the current launch wizard code it seems like you wouldn't need to load all that data for the wizard to be displayed, since only some subset of it would be necessary to display any given panel of the wizard.

 
    I tend to lean towards your POV and starting with discrete API calls and letting the client optimize calls.  If there are performance problems or other reasons then doing data aggregation on the server side could be considered at that point.

I'm glad to hear it. I'm a fan of optimising when necessary, and not beforehand :)

 
    Of course if anybody is able to do some performance testing between the two approaches then that could affect the direction taken.

I would certainly like to see us take some measurements when performance issues pop up. Optimising without solid metrics is bad idea :)


    Richard
 
      Thanks for the great summary, Travis.

      I've completed the work I pledged this morning, so now the REST API change set has:

      - no rest framework dependency
      - AJAX scaffolding in openstack_dashboard.api.rest.utils
      - code in openstack_dashboard/api/rest/
      - renamed the API from "identity" to "keystone" to be consistent
      - added a sample of testing, mostly for my own sanity to check things were working

      https://review.openstack.org/#/c/136676


            Richard

      On Wed Nov 26 2014 at 12:18:25 PM Tripp, Travis S <travis.tr...@hp.com> wrote:
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--
Regards,
Tihomir Trifonov
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--
Regards,
Tihomir Trifonov
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