Resource Providers - Filtered Resource Providers by Request

https://blueprints.launchpad.net/nova/+spec/resource-providers-get-by-request

This blueprint aims to modify the POST method of the resource_providers REST resource so that it returns a list of resource providers that can support the list of requested resource classes.

Problem description

There is currently no way to get a list of resource providers that can fulfill a set of requested resources by verifying that the respective inventories can support the existing allocation plus the requested overhead. That work is a necessary prerequisite for the scheduler being able to call the placement API in order to narrow the list of acceptable hosts before calling the filters.

Use Cases

None.

Proposed change

We propose to change the existing /resource_providers REST resource to support a method providing a request body that would describe a list of requested amounts of resource classes and would return a list of resource providers supporting those amounts.

To be clear, the math for knowing whether a resource provider is acceptable would be, for each resource class, take the related inventory, lookup the allocations against that inventory and make sure that the amount of free resource for the inventory is more or equal than the requested amount, with respect to the defined allocation ratio and the reserved size.

Alternatives

There can be many ways to provide a solution for getting a list of resource providers but given we prefer to review the implementation rather than nitpicking which HTTP method or which REST resource could be the best, I prefer to add a disclaimer below.

Data model impact

None.

REST API impact

Warning

The following REST API proposal is a possible solution that will be reviewed during the implementation. That means that the REST resource or the HTTP method could be eventually different in the Nova tree, implying that this spec would be amended in a later change.

The following new REST API call will be modified:

POST /resource_providers

The POST method for that /resource_providers REST resource will now accept a new query string in the URI called ‘request’ that will return a list of all the resource providers accepted a list of resource requirements.

Example:

POST /resource_providers?request

The body of the request must match the following JSONSchema document:

{
    "type": "object",
    "properties": {
       "resources": {
         "type": "object",
         "patternProperties": {
           "^[0-9a-fA-F-]+$": {
             "type": "object",
             "patternProperties": {
               "^[A-Z_]+$": {"type": "integer"}
             }
           },
           "additionalProperties": false
         }
    },
    "required": [
        "resources"
    ]
    "additionalProperties": False
}

For example, a request body asking for VCPUs and RAM would look like:

POST /resource_providers?request
{
   "resources": {
     "VCPU": 2,
     "MEMORY_MB": 1024
   }
}

The response would be:

200 OK
Content-Type: application/json

{
  "resource_providers": [
    {
      "uuid": "b6b065cc-fcd9-4342-a7b0-2aed2d146518",
      "name": "RBD volume group",
      "generation": 12,
      "links": [
         {
           "rel": "self",
           "href": "/resource_providers/b6b065cc-fcd9-4342-a7b0-2aed2d146518"
         },
         {
           "rel": "inventories",
           "href": "/resource_providers/b6b065cc-fcd9-4342-a7b0-2aed2d146518/inventories"
         },
         {
           "rel": "aggregates",
           "href": "resource_providers/b6b065cc-fcd9-4342-a7b0-2aed2d146518/aggregates"
         },
         {
           "rel": "usages",
           "href": "resource_providers/b6b065cc-fcd9-4342-a7b0-2aed2d146518/usages"
         }
      ]
    },
    {
      "uuid": "eaaf1c04-ced2-40e4-89a2-87edded06d64",
      "name": "Global NFS share",
      "generation": 4,
      "links": [
         {
           "rel": "self",
           "href": "/resource_providers/eaaf1c04-ced2-40e4-89a2-87edded06d64"
         },
         {
           "rel": "inventories",
           "href": "/resource_providers/eaaf1c04-ced2-40e4-89a2-87edded06d64/inventories"
         },
         {
           "rel": "aggregates",
           "href": "resource_providers/eaaf1c04-ced2-40e4-89a2-87edded06d64/aggregates"
         },
         {
           "rel": "usages",
           "href": "resource_providers/eaaf1c04-ced2-40e4-89a2-87edded06d64/usages"
         }
      ]
    }
  ]
}

In case a requested resource class doesn’t exist, a HTTP400 will be returned.

Security impact

None.

Notifications impact

None.

Other end user impact

None.

Performance Impact

None.

Other deployer impact

None.

Developer impact

None.

Implementation

Assignee(s)

Primary assignee:

bauzas

Other contributors:

cdent jaypipes

Work Items

• Write the math

• Expose the API change

Dependencies

None.

Testing

Gabbi functional tests will cover that.

Documentation Impact

Of course, we should amend the docs that we need to write anyway.

References

None.