[openstack-dev] [quantum] [LBaaS] Health monitors REST resource
Youcef Laribi
Youcef.Laribi at eu.citrix.com
Wed Nov 21 20:12:17 UTC 2012
Hi Salvatore,
Thank you for your thorough analysis and helping the team reconcile a good API design with an easy way to implement it.
I think we need to make a distinction between pool members and health monitors.
Indeed the former exist only within a pool [1], whereas the latter can be defined without any pool [2].
So for the pool members, I agree we probably don't want to specify them in API calls for 'pool' resources.
In particular [3] seems strange in my opinion, as it is assuming the members already exist. In another thread I think there was a suggestion to make the member's pool_id attribute optional, but my opinion is that probably we should remove the members attribute for the pool resource (at least on create/update calls). It is fine IMHO to return a list of member ids on GET operations for pools.
Yes today we have two ways of putting members into pools:
1. Create an empty pool, and then create members using the created pool_id
2. Create members (with no pool_id) and then create a pool containing those members
We can eliminate the second workflow to simplify as you suggested, so there would be only one way of creating members in pools.
The question after this, is how do I get the members of a pool (a very common operation). Here again, we have three possible ways:
1. Use filtering: GET /members?pool_id=1000
2. Have a dedicated REST API that reflects the fact the members belong to a pool: GET /pools/1000/members
3. Return the list of members of a pool in the pool response payload of: GET /pools/1000
I favor the second approach but I can settle for the 3rd one, even though this requires more work from a user to find the "members" attribute on the response. What is your opinion on this?
Instead the health monitors are slightly different, since they are in a n:m relationship with the pool resource. pool and pool members are instead on a 1:n relationship.
The approach currently adopted in the API specification [4] makes sense from a REST perspective. IMHO it makes more sense than having distinct member action such as:
PUT /pools/<pool-id>/associate_health_monitor and PUT /pools/<pool-id>/disassociate_health_monitor. As some contributors to this thread have pointed out, this can generate confusion in final users, as they might wonder whether an id or a full object definition is required. In that case I would consider the following:
{POST/DELETE} /pools/<pool-id>/health_monitor_ids
Sub-resources map very well onto a ORM model.
Yes we are on the same page here, although I favor calling the sub-resource simply "health_monitors" instead of "health_monitor_ids" or "health_monitor_references", purely from an aesthetic perspective, but I haven't got a strong opinion on this.
However, let's imagine you want to retrieve the list of pools which are using a health_monitor. How would you do that? In theory you could add that filter to the pools resource, so:
GET /pools?health_monitor_id=<your_health_monitor> would return you this kind of list.
With this approach it is important to keep in mind is that a GET /pools is supposed to look only into 'pool' resources. Adding this kind of capability would require us to do joins according to the type of filter specified (and we will also have to document it). No big deal, but still something to keep in mind.
Yes this call doesn't make sense since there is currently no attribute called "health_monitor_id" in a pool resource you can filter on. User can accomplish this themselves by retrieving all pool's health monitor associations, and filtering the ones that contain the health_monitor of interest
GET /pools/1000/health_monitors
GET /pools/2000/health_monitors
Etc.
After all, these kind of request "which pools use monitor X" are not very common or necessary for the workflow of the service. There would be a lot many more questions like this that cannot be directly mapped to an API call, and need the user to do some filtering and joining on their own.
An alternative is to regard the health_monitor as a 'template'. I am not sure if this is valid within the LB world, but I have the impression it is ok to assume that a health monitor does not actually exist until it is associated with a pool.
In NetScaler, F5 and similar products, health monitors are created beforehand just like in the API, and then they are "bound" to pools (our association API), so the mapping will be more natural.
In this case 'definitions' for health monitors could be managed in the following way:
{ GET/POST/PUT/DELETE } /health-monitor-templates
And association/disassociation with pools can be managed in the following way:
{GET/POST/DELETE} /health-monitors
The response here would look like the following:
{
"health_monitor_id": "uuid",
"health_monitor_template_id": "another-uuid",
"pool_id": "yet-another-uuid"
}
I think both approaches are equivalent. The first is represents a good mapping on the ORM model, while the second a mapping on the ER model.
The first will need work to the Quantum's framework, whereas the latter can be implemented using the framework as it is.
I have a slight preference for the second option, but no strong opinion, as I believe the first approach makes sense too.
I think adding a concept of health_monitor templates just complicate matters even more. The issue we have is not how to associate monitors and pools, these are simple API calls, but answering the following questions
1. What are the health_monitors associated with a pool?
2. What are the pools associated with a health monitor?
I propose when retrieving a pool, we simply return the list of health_monitors associated with it, and for a health_monitor the list of pools associated with it. These are only returned for GET (they are read-only attributes), they are not used for creation or update (we use the associate/dissociate APIs already there), so this would translate in answering the above questions to this:
1. Health monitors associated with a pool: GET /pools/{pool_id} (response contains a "health_monitors" (or health_monitor_ids :)) attribute)
2. Pools associated with a health_monitor: GET /health_monitors/{health_monitor_id} (response contains a "pools" attribute)
This way we avoid the issue of sub-resource modeling, and keep the API simple (at a cost of slightly more work for the API caller). What do you think?
Youcef
On 20 November 2012 09:51, Oleg Bondarev <obondarev at mirantis.com<mailto:obondarev at mirantis.com>> wrote:
Hi Youcef, team,
AFAIK python clients (quantum, nova, etc.) usually expose both CLI and python API which I believe should be used in Horizon and other projects. So I still think that python-quantumclient is the right place for adding shortcuts.
A agree that improving api/v2 to support sub-resources is a good idea and will be useful. I also agree that "GET /v1.0/pools/{pool_id}/members" looks natural but only in case when member is an actual sub-resource of a pool. Resources and sub-resources in the Quantum extension framework are distinctly separated. In our case members and health monitors are top level resources - so adding them also as sub-resources is kind of hack, and may be misleading for those who reads the code - all for the sake of having shortcuts in REST.
>From my point of view it's clear enough from our REST API that members belong to a pool since they have pool_id field and pool in its turn has members field.
Hey we have a pretty long discussion here :), would be great to hear anybody else from the team and make a final decision.
Salvatore, could you please share your thoughts?
Thanks,
Oleg
From: Youcef Laribi [mailto:Youcef.Laribi at eu.citrix.com<mailto:Youcef.Laribi at eu.citrix.com>]
Sent: Tuesday, November 20, 2012 1:01 AM
To: OpenStack Development Mailing List
Subject: Re: [openstack-dev] [quantum] [LBaaS] Health monitors REST resource
Yes Oleg, some people will use the CLI to drive the LBaaS service, Horizon portal will use the API, and other applications will use mainly the API. Most people will understand the service by reading its APIs.
Yes, you can list the members of pool 1000 through query string filtering by doing:
GET /v1.0/members?pool_id=1000
But as I said before, it's more natural to use the following to get the pool's members:
GET /v1.0/pools/{pool_id}/members
Since members really belong to a pool. As you said, if we are improving Quantum to support REST sub-resources then this is the preferred approach I would advocate.
Youcef
From: Oleg Bondarev [mailto:obondarev at mirantis.com]<mailto:[mailto:obondarev at mirantis.com]>
Sent: Monday, November 19, 2012 1:23 AM
To: 'OpenStack Development Mailing List'
Subject: Re: [openstack-dev] [quantum] [LBaaS] Health monitors REST resource
I also surely agree that "/pools/{pool_id}/health_monitor_references" looks ugly and I don't want it to look like this.
My only concern is that treating health monitor references as a sub-resource (and hence changes in api/v2) brings additional complexity to the code when it can be done simpler: using filters for listing health monitors of a pool and member actions for associate/disassociate (as in l3 extension). But probably it is ok given that handling sub-resources may be useful in future anyway.
Another question I have is: where will these REST calls be used except python-quantumclient? I thought that only client api matters for end users. So the purpose of having kind of shortcuts for listing members and health monitors of a pool in REST API (instead of using filters) is not completely clear for me.
Thanks,
Oleg
From: Salvatore Orlando [mailto:sorlando at nicira.com]
Sent: Friday, November 16, 2012 9:32 PM
To: OpenStack Development Mailing List
Subject: Re: [openstack-dev] [quantum] [LBaaS] Health monitors REST resource
Hi Youcef,
Thanks for the clarification. I was pretty sure this was well thought in the API design, as I wrote in my previous post :)
The naming for the attribute on the pool which references health_monitors is a discussion worth having. I have very little data points for comparison with other parts of Quantum and Openstack APIs. The only similar bit is probably the network-subnet relationship. In the response for a GET /networks/<network-id> a list of subnet identifiers is returned. The name for the list attribute is just 'subnets'. However, as this is a read-only attribute there is no need for handling it as a sub-resource. Response sample is available at [1]
Between handling the collection of health monitor references as a sub-resource and having member actions for CRUD operations, I prefer the first solution. I am happy to offer any kind of supports for the relevant changes in the apiv2 modules. The other option is to regard health_monitors as a 'list' attribute. Which means that a POST/PUT will create/update the whole list. This is practical from server-side perspective, but has also drawbacks. Indeed it adds burden to the client; for instance, in order to add an element to the list you'll need a GET and then a PUT; and it also causes confusion because of the fact that our PUT actually implement patch semantics.
Salvatore
[1] http://docs.openstack.org/api/openstack-network/2.0/content/List_Networks_Detail.html#d6e858
On 16 November 2012 18:04, Youcef Laribi <Youcef.Laribi at eu.citrix.com<mailto:Youcef.Laribi at eu.citrix.com>> wrote:
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<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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