Symmetric GET and PUT of allocations in Placement

Symmetric GET and PUT of allocations in Placement

https://blueprints.launchpad.net/nova/+spec/symmetric-allocations

When support for placement allocations was added on the nova-side (initially in the resource tracker) the formats of the representations used in GET and PUT diverged. GET took on a dict oriented style, and PUT a list oriented style. Since then this disparity has caused confusion. A dict style is considered easier to work with, so a new microversion will be created to support that form.

Problem description

The Generic Resource Pools specification describes the representations used in the response and request bodies of GET and PUT /allocations/{consumer_uuid}. Not only are these not the same (usually desirable) they are fundamentally different: one is based on a dict, the other uses items in a list.

This came about because when support for GET was added in change I69fbc4e9834ec6dc80dacf43f8fd9dc6ec139006 it was built to address the specific needs of the caller, where inspecting the data by key was most useful. Since then this format has been declared the most usable and it has been discovered that retrieving allocations, manipulating them, and sending them back is relatively common. So we should fix it.

This problem was initially registered in bug 1708204 and has become more relevant with the desire to resolve the post-allocations blueprint, which expresses a preference to use the dict-based format, and we should be consistent.

Use Cases

As a user of the Placement API, I would like representations to be consistent for read and write, and formatted for most effective use.

Proposed change

The JSON schema for the request body to PUT /allocations/{consumer_uuid} will be versioned (in a new Placement service microversion) to expect data to be input in the same form as retrieved from GET /allocations/{consumer_uuid}. The format is described below.

Because writing allocations requires project_id and user_id information, the response body of GET /allocations/{consumer_uuid} will be extended to include those fields.

Similarly, because the response to a GET /allocation_candidates includes an allocation_requests property that includes a series of JSON objects that are designed to be opaquely sent as bodies in PUT /allocations/{consumer_uuid}, the format of that response will be updated in the same microversion to reflect the dict-based format. See example below.

Alternatives

The main alternative is to do nothing.

Data model impact

None.

REST API impact

The existing JSON schema for the request body to PUT /allocations/{consumer_uuid} will be updated to expect data in the following form:

{
    "allocations": {
        "RP_UUID_1": {
            "generation": GENERATION,
            "resources": {
                "DISK_GB": 4,
                "VCPU": 2
            }
        },
        "RP_UUID_2": {
            "generation": GENERATION,
            "resources": {
                "DISK_GB": 6,
                "VCPU": 3
            }
       }
     },
     "project_id": "PROJECT_ID",
     "user_id": "USER_ID"
}

generation is optional and if present will be ignored. It is allowed to preserve symmetry. To further preserve symmetry the response to a GET on the same URL will include the project_id and user_id fields.

The response body for GET /allocation_candidates will be updated so that the allocation_requests object will change from the following list-based format (the surrounding JSON, including provider summaries has been excluded, see the list allocation candidates docs for more detail on the full response body):

"allocation_requests": [
    {
        "allocations": [
            {
                "resource_provider": {
                    "uuid": "RP_UUID_1"
                },
                "resources": {
                    "MEMORY_MB": 512
                }
            },
            {
                "resource_provider": {
                    "uuid": "RP_UUID_2"
                },
                "resources": {
                    "DISK_GB": 1024
                }
            }
        ]
    },
    {
        "allocations": [
            {
                "resource_provider": {
                    "uuid": "RP_UUID_3"
                },
                "resources": {
                    "MEMORY_MB": 512,
                    "DISK_GB": 1024
                }
            }
        ]
    }
],

to the new dict based format:

"allocation_requests": [
    {
        "allocations": {
            "RP_UUID_1": {
                "resources": {
                    "MEMORY_MB": 512
                }
            },
            "RP_UUID_2": {
                "resources": {
                    "DISK_GB": 1024
                }
            }
        }
    },
    {
        "allocations": {
            "RP_UUID_3": {
                "resources": {
                    "MEMORY_MB": 512,
                    "DISK_GB": 1024
                }
            }
        }
    }
],

Security impact

None.

Notifications impact

None.

Other end user impact

None.

Performance Impact

None.

Other deployer impact

None.

Developer impact

Developers will now have a choice of formats (by specifying the appropriate microversion) when sending allocations to the Placement service.

At some point, either during the implementation of this spec, or later as people find it worth doing, the microversion used when sending allocations from the scheduler report client should be updated.

Implementation

Assignee(s)

Primary assignee:

cdent

Other contributors:

you

Work Items

  • Write JSON schema representing the desired format.

  • Add support for a new microversion which validates PUT /allocations/{consumer_uuid} bodies against that new schema.

  • Modify GET /allocations/{consumer_uuid} to include project_id and user_id.

  • Modify GET /allocation_candidates to send the dict-based format.

  • Integrate processing that data to compose a call to AllocationList.create_all().

  • Add gabbi tests exercising the new microversion.

  • Add placement-api-ref documentation for the new microversion.

Dependencies

None.

Testing

Care should be taken to insure that tests cover the boundary cases of microversion handling.

Documentation Impact

The main documentation impact is in the placement api-ref where a new microversion will need to be described for PUT /allocations/{consumer_uuid}.

References

History

Revisions

Release Name

Description

Queens

Introduced

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