[openstack-dev] [quantum] [LBaaS] Health monitors REST resource
Youcef Laribi
Youcef.Laribi at eu.citrix.com
Fri Nov 16 17:04:51 UTC 2012
Changing the subject line...
Health monitors "/health_monitors/" are a top resource in the API and are retrieved/added/removed/updated through their CRUD operations on this top resource.
The subresource "/pools/{pool_id}/health_monitors" is used for associating already existing health monitors (created above) with an existing pool, or for retrieving the health monitors associated with a pool. It is a collection (list) that only contain IDs of health monitors not the health monitors themselves. We can call this resource "/pools/{pool_id}/health_monitor_references" or "/pools/{pool_id}/pool_health_monitors" if we like, but I felt this was ugly and I think there is no issue or ambiguity in the definition of API itself as all operations are clearly described. But if you think changing its name helps, I can do that :) Would like to hear what others in the team think.
Youcef
From: Oleg Bondarev [mailto:obondarev at mirantis.com]
Sent: Friday, November 16, 2012 1:12 AM
To: Youcef Laribi; 'OpenStack Development Mailing List'
Subject: RE: [openstack-dev] [quantum] Quantum extension framework issue
Hi guys,
I just want to clarify some things regarding health monitors in LBaaS API: actually it is not completely a sub-resource of pool objects.
According to the API it is a separate resource which can be added/showed/updated/deleted (with GET/POST.. "/v1.0/health_monitors/.." rest calls) in order to be reusable in different pools and probably anywhere else as Sasha mentioned. Youcef please correct me if I am wrong here.
Speaking about sub-resources I think following rest call:
POST /v1.0/pools/{pool_id}/health_monitors
is intended to create a sub-resource of health monitor for the pool and not to add an existing health monitor to the pool.
Also I think having health monitors as a separate resource and as a sub-resource of a pool at the same time is not correct.
So my vision is to leave health monitors as a separate resource and to use member actions for the purpose of getting/associating/disassociating health monitors with a pool:
Get health monitors of a pool:
GET /v1.0/pools/{pool_id}/get_health_monitors
Associate health monitors with a pool:
PUT /v1.0/pools/{pool_id}/add_health_monitors
{
"health_monitors" : [
"f3eeab00-8367-4524-b662-55e64d4cacb5"
]
}
Disassociate health monitors from a pool:
PUT /v1.0/pools/{pool_id}/delete_health_monitors
{
"health_monitors" : [
"f3eeab00-8367-4524-b662-55e64d4cacb5"
]
}
Please share your thoughts.
Thanks,
Oleg
From: Sasha Ratkovic [mailto:sasharatkovic at juniper.net]
Sent: Friday, November 16, 2012 3:38 AM
To: OpenStack Development Mailing List
Subject: Re: [openstack-dev] [quantum] Quantum extension framework issue
One comment: even though health_monitor is introduced as part of LB effort, it has more general applicability. So having it under LB specific resource may pose usability problems down the road when new services are introduced, if health monitor is to be re-used for that purpose. One solution is to make it "first class" citizen with relationship to "pool" and/or make "pool" assume more abstract pooling semantics, reusable as well across multiple services in the future. (yes, I am talking about "groups" here :) ).
From: Salvatore Orlando <sorlando at nicira.com<mailto:sorlando at nicira.com>>
Reply-To: OpenStack Development Mailing List <openstack-dev at lists.openstack.org<mailto:openstack-dev at lists.openstack.org>>
Date: Thursday, November 15, 2012 7:40 AM
To: OpenStack Development Mailing List <openstack-dev at lists.openstack.org<mailto:openstack-dev at lists.openstack.org>>
Subject: Re: [openstack-dev] [quantum] Quantum extension framework issue
Hi Oleg,
This is exactly what I was talking about.
One thing you might want to consider before choosing for one direction or the other is that at the moment Quantum API does not use sub resources at all.
There was a long discussion on this regard while designing the v2 API. The gist of the discussion was that if a resource needed sub-resources then there was a case for a sub-resource to become a 'first citizen' in the API. I am pretty sure you already have mulled over whether health_monitors should be a resource of their own, a sub resource of the pool, or a multi-valued attribute of the pool, but I wanted to give you a heads-up anyway.
On your technical questions I have some answers inline.
Salvatore
On 15 November 2012 15:40, Oleg Bondarev <obondarev at mirantis.com<mailto:obondarev at mirantis.com>> wrote:
Hi folks,
As Salvatore said there is a way to specify parent for a resource (see quantum.extensions.extensions.ResourceExtension) which allows route mapping for rest calls like:
POST /v1.0/pools/{pool_id}/health_monitors
DELETE /v1.0/pools/{pool_id}/health_monitors/{id}
...
In this case corresponding resource controller should be aware of resource parent and be able to handle CRUD operations with an additional parent_id parameter. Currently it doesn't. Actually I am speaking about quantum.api.v2.base.Controller - so, Salvatore, do you think it is the right place to include sub-resource/parent handling?
Working on controllers in quantum.api.v2 is the best option in my opinion.
This however depends on how the route mapper associates controllers with sub resources. Currently, the extension framework and the core API use two distinct code paths: the former uses quantum.extensions.extensions.ExtensionMiddleware whereas the latter uses quantum.api.v2.router.APIRouter (this is for historical reasons only; as far as I can recall, there's no technical reason for this). The Extension Middleware has a mechanism for mapping associating parent resources to a mapped resource, whereas the APIRouter does not have such mechanism.
As the controller does not care about how URI paths are mapped on its methods, the only thing we probably need to worry about is how to make sure that the parent resource id is passed to the controller for the sub-resource. To this aim, I would probably define a new controller which extends the base one rather than modifying quantum.api.v2.base.Controller.
Btw, there is of course the hackish way of skipping base.create_resource and passing to ResourceExtension an object providing implementation for the appropriate methods. I am totally sure you're aware of this option too, but I would consider it only a last resort.
And also how do you guys think should this improvement be done as a separate patch?
Separate patches in these cases are always preferred.
Thanks,
Oleg
From: Youcef Laribi [mailto:Youcef.Laribi at eu.citrix.com<mailto:Youcef.Laribi at eu.citrix.com>]
Sent: Wednesday, November 14, 2012 11:03 PM
To: OpenStack Development Mailing List
Subject: Re: [openstack-dev] [quantum] Quantum extension framework issue
Oleg,
The "/pools/{pool_id}/health_monitors" REST resource is intended to be a collection sub-resource of the "/pools/{pool_id}" resource, so if the Quantum WSGI framework can be improved to support REST sub-resources that would be better and cleaner.
Youcef
From: Salvatore Orlando [mailto:sorlando at nicira.com]<mailto:[mailto:sorlando at nicira.com]>
Sent: Wednesday, November 14, 2012 10:00 AM
To: OpenStack Development Mailing List
Subject: Re: [openstack-dev] [quantum] Quantum extension framework issue
Hi Oleg,
When I read your first email, I had the same impression as Dan.
health_monitors look more like a subresource than an action.
The WSGI framework at the moment is not able to manage subresources; this does not mean we cannot improve it though. Nevertheless, in this case the route mapping is not performed by the API classes in quantum/api, but by the extension manager. I think there should already be a way for specifying parent resources with extensions, but that needs to be explored.
It seems however that you are now trying to map operations on health monitors using distinct member actions (add_health_monitor, get_health_monitors). This is similar to what happens with the L3 API for router interfaces.
However, it seems the original idea behind the API design was to treat health_monitors as an explicit collection, which would also be probably a more 'restful' way of doing it. I think ultimately the question should be directed to Youcef and the team which contributed to the design of the LBaaS API.
On 14 November 2012 17:18, Oleg Bondarev <obondarev at mirantis.com<mailto:obondarev at mirantis.com>> wrote:
Hi Dan,
Thanks for your comment here.
Just wanted to correct a mistake in my first email: of course there can't be a dict with duplicate keys. The idea was to use list of pairs, like:
member_actions = [{"health_monitors": "GET"},
{"health_monitors": "POST"}]
to have an ability of using same function name with different request actions. Initially I thought that the framework provides such ability but does not dispatch requests correctly. I was wrong.
Actually there is no issue with the framework as it assumes using unique action names for different request methods.
I believe we should update LBaaS REST API doc and use "get_health_monitors", "add_health_monitors", etc. to fit in the framework.
Thanks,
Oleg
From: Dan Wendlandt [mailto:dan at nicira.com<mailto:dan at nicira.com>]
Sent: Wednesday, November 14, 2012 7:27 PM
To: OpenStack Development Mailing List
Subject: Re: [openstack-dev] [quantum] Quantum extension framework issue
Hi Oleg,
Folks from the API-subteam can correct me, but I believe this use model is outside of what the API framework was trying to enable with "actions". The idea is that you use POST/DELETE to create an delete API "resources" (which actually have UUIDs, for example, the "pool" in your example below) and then do a PUT to an "action" to cause some kind of change that you can affect on a resource (e.g., "add_health_monitor" or "remove_health_monitor"). It sounds like what you are proposing is more treating "health_monitors" almost as a "sub-resource", which is not really what the "actions" stuff was designed for.
I haven't been deeply involved in the LBaaS api design discussion though, so I'd also like to hear from Salvatore, et al. on the API sub-team.
Dan
On Wed, Nov 14, 2012 at 6:05 AM, Oleg Bondarev <obondarev at mirantis.com<mailto:obondarev at mirantis.com>> wrote:
Hi guys,
While working on the API extension for LBaaS I didn't find a way to use custom member actions if they have the same name and differ only by request method, for example
List all health monitors of a specific pool: GET /pool/pool_id/health_monitors
Associate health monitors with a pool: POST /pool/pool_id/health_monitors
In quantum extension framework we pass "health_monitors" as member actions for a controller (quantum.api.v2.base.create_resource())
member_actions = {'health_monitors': 'GET',
'health_monitors': 'POST'}
controller = base.create_resource(collection_name,
resource_name,
plugin, params,
member_actions=member_actions)
According to the Controller implementation it dispatches all custom member actions to its plugin attr:
def __getattr__(self, name):
if name in self._member_actions:
def _handle_action(request, id, body=None):
return getattr(self._plugin, name)(request.context, id, body)
return _handle_action
else:
raise AttributeError
Where request.context is of type quantum.context.Context and does not contain info about request method.
As a result there is no way to distinguish two custom actions in the plugin.
Is it an issue in the framework?
Possible solution may be in concatenation of request method and action name ("get_health_monitors", "post_health_monitors") in a controller before dispatching them to a plugin.
What do you think?
Thanks,
Oleg
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