Support any traits in allocation_candidates query

Support any traits in allocation_candidates query

The GET /allocation_candidates request in Placement supports the required query parameter. If the caller specifies a list of traits in the required parameter then placement will limit the returned allocation candidates to those RP trees that fulfill every traits in that list. To support minimum bandwidth guarantees in Neutron + Nova we need to be able to query allocation candidates that fulfill at least one trait from a list of traits specified in the query. This is required for the case when a Neutron network maps to more than one physnets but the port’s bandwidth request can be fulfilled from any physnet the port’s network maps to.

Problem description

Neutron through Nova needs to be able to query Placement for allocation candidates that are matching to at least one trait from the list of traits provided in the query.

Use Cases

Neutron wants to use this any(traits) query to express that a port’s bandwidth resource request needs to be fulfilled by a Network device RP that is connected to one of the physnets the network of the given port is connected to. With Neutron’s multiprovider network extension a single Neutron network can consist of multiple network segments connected to different physnets.

Proposed change

Extend the GET /allocation_candidates and GET /resource_providers requests with a new required=in:TRAIT1,TRAIT2 query parameter syntax and change the placement implementation to support this new syntax.

The granular-resource-requests spec proposes support for multiple request groups in the Placement query identified by a positive integer postfix in the required query param. The new in:TRAIT1,TRAIT2 syntax is applicable to the required<N> query params as well.



Data model impact


REST API impact

Today the GET /allocation_candidates and GET /resource_providers query support the required query param in the form of required=TRAIT1,TRAIT2,!TRAIT3. This spec proposes to implement a new microversion to allow the format of required=in:TRAIT1,TRAIT2 as well as the old format.

Each resource provider returned from a request having required=in:TRAIT1,TRAIT2 should have at least one matching trait from TRAIT1 and TRAIT2.

required=in:TRAIT1,TRAIT2 used in a GET /allocation_candidates query means that the union of all the traits across all the providers in every allocation candidate must contain at least one of T1, T2.

requiredX=in:TRAIT1,TRAIT2 used in a GET /allocation_candidates query means that the resource provider that satisfies the requirement of the granular request group X must also has at least one of T1, T2.

The response body of the GET /allocation_candidates and GET /resource_providers query are unchanged.

A separate subsequent spec will propose to support repeating the required query param more than once to allow mixing the two formats.

Note that mixing required and forbidden trait requirements in the same required=in: query param, like required=in:TRAIT1,!TRAIT2 will not be supported and will result a HTTP 400 response.

Security impact


Notifications impact


Other end user impact

The osc-placement client plugin needs to be updated to support the new Placement API microversion. That plugin currently support the –required CLI parameter accepting a list of traits. So this patch propose to extend that parameter to accept in:TRAIT1,TRAIT2 format.

Performance Impact


Other deployer impact


Developer impact


Upgrade impact




Primary assignee:


Work Items

  • Extend the resource provider and allocation candidate DB query to support the new type of query

  • Extend the Placement REST API with a new microversion that supports the any trait syntax

  • Extend the osc-placement client plugin to support the new microversion


  • the osc-placement client plugin can only be extended with the new microversion support if every older microversion is already supported which is not the case today.


Both new gabbi and functional tests needs to be written for the Placement API change. Also the osc-placement client plugin will need additional functional test coverage.

Documentation Impact

The Placement API reference needs to be updated.


  • osc-placement review series adding support for latest Placement microversions



Release Name






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