Support Consumer Types

Support Consumer Types

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This spec aims at providing support for services to model consumer types in placement. While placement defines a consumer to be an entity consuming resources from a provider it does not provide a way to identify similar “types” of consumers and henceforth allow services to group/query them based on their types. This spec proposes to associate each consumer to a particular type defined by the service owning the consumer.

Problem description

In today’s placement world each allocation posted by a service is against a provider for a consumer (ex: for an instance or a migration). However a service may want to distinguish amongst the allocations made against its various types of consumers (ex: nova may want to fetch allocations against instances alone). This is currently not possible in placement and hence the goal is to make placement aware of “types of consumers” for the services.

Use Cases

  • Nova using placement as its quota calculation system: Currently this approach uses the nova_api database to calculate the quota on the “number of instances”. In order for nova to be able to use placement to count the number of “instance-consumers”, there needs to be a way by which we can differentiate “instance-consumers” from “migration-consumers”.

  • Ironic wanting to differentiate between “standalone-consumer” versus “nova-consumer”.

Note that it is not within the scope of placement to model the coordination of the consumer type collisions that may arise between multiple services during their definition. Placement will also not be able to identify or verify correct consumer types (eg, INTANCE versus INSTANCE) from the external service’s perspective.

Proposed change

In order to model consumer types in placement, we will add a new consumer_types table to the placement database which will have two columns:

  1. an id which will be of type integer.

  2. a name which will be of type varchar (maximum of 255 characters) and this will have a unique constraint on it. The pattern restrictions for the name will be similar to placement traits and resource class names, i.e restricted to only ^[A-Z0-9_]+$ with length restrictions being {1, 255}.

A sample look of such a table would be:

id

name

1

UNKNOWN

2

INSTANCE

3

MIGRATION

A new column called consumer_type_id would be added to the consumers table to map the consumer to its type.

The POST /allocations and PUT /allocations/{consumer_uuid} REST API’s will gain a new (required) key called consumer_type which is of type string in their request body’s through which the caller can specify what type of consumer it is creating or updating the allocations for. If the specified consumer_type key is not present in the consumer_types table, a new entry will be created. Also note that once a consumer type is created, it lives on forever. If this becomes a problem in the future for the operators a tool can be provided to clean them up.

In order to maintain parity between the request format of PUT /allocations/{consumer_uuid} and response format of GET /allocations/{consumer_uuid}, the consumer_type key will also be exposed through the response of GET /allocations/{consumer_uuid} request.

The external services will be able to leverage this consumer_type key through the GET /usages REST API which will have a change in the format of its request and response. The request will gain a new optional key called consumer_type which will enable users to query usages based on the consumer type. The response will group the resource usages by the specified consumer_type (if consumer_type key is not specified it will return the usages for all the consumer_types) meaning it will gain a new consumer_type key. Per consumer type we will also return a consumer_count of consumers of that type.

See the API impact section for more details on how this would be done.

The above REST API changes and the corresponding changes to the /reshaper REST API will be available from a new microversion.

The existing consumers in placement would be mapped to a default consumer type called UNKNOWN (which will be the default value while creating the model schema) which means we do not know what type these consumers are and the service to which the consumers belong to needs to update this information if it wants to avail the consumer_types feature.

Alternatives

We could create a new REST API to allow users to create consumer types explicitly but it does not make sense to add a new API for a non-user facing feature.

Data model impact

The placement database will get a new consumer_types table that will have a default consumer type called UNKNOWN and the consumers table will get a new consumer_type_id column that by default will point to the UNKNOWN consumer type. The migration is intended to solely be an alembic migration although a comparision can be done for this versus having a seperate online data migration to update null values to “UNKNOWN” to pick the faster one.

API impact

The new POST /allocations request will look like this:

{
  "30328d13-e299-4a93-a102-61e4ccabe474": {
    "consumer_generation": 1,
    "project_id": "131d4efb-abc0-4872-9b92-8c8b9dc4320f",
    "user_id": "131d4efb-abc0-4872-9b92-8c8b9dc4320f",
    "consumer_type": "INSTANCE", # This is new
    "allocations": {
      "e10927c4-8bc9-465d-ac60-d2f79f7e4a00": {
        "resources": {
          "VCPU": 2,
          "MEMORY_MB": 3
        },
        "generation": 4
      }
    }
  },
  "71921e4e-1629-4c5b-bf8d-338d915d2ef3": {
    "consumer_generation": 1,
    "project_id": "131d4efb-abc0-4872-9b92-8c8b9dc4320f",
    "user_id": "131d4efb-abc0-4872-9b92-8c8b9dc4320f",
    "consumer_type": "MIGRATION", # This is new
    "allocations": {}
  },
  "48c1d40f-45d8-4947-8d46-52b4e1326df8": {
    "consumer_generation": 1,
    "project_id": "131d4efb-abc0-4872-9b92-8c8b9dc4320f",
    "user_id": "131d4efb-abc0-4872-9b92-8c8b9dc4320f",
    "consumer_type": "UNKNOWN", # This is new
    "allocations": {
      "e10927c4-8bc9-465d-ac60-d2f79f7e4a00": {
        "resources": {
          "VCPU": 4,
          "MEMORY_MB": 5
        },
        "generation": 12
      }
    }
  }
}

The new PUT /allocations/{consumer_uuid} request will look like this:

{
  "allocations": {
    "4e061c03-611e-4caa-bf26-999dcff4284e": {
      "resources": {
        "DISK_GB": 20
      }
    },
    "89873422-1373-46e5-b467-f0c5e6acf08f": {
      "resources": {
        "MEMORY_MB": 1024,
        "VCPU": 1
      }
    }
  },
  "consumer_generation": 1,
  "user_id": "66cb2f29-c86d-47c3-8af5-69ae7b778c70",
  "project_id": "42a32c07-3eeb-4401-9373-68a8cdca6784",
  "consumer_type": "INSTANCE" # This is new
}

Note that consumer_type is a required key for both these requests at this microversion.

The new GET /usages response will look like this for a request of type GET /usages?project_id=<project id>&user_id=<user id> or GET /usages?project_id=<project id> where the consumer_type key is not specified:

{
    "usages": {
      "INSTANCE": {
          "consumer_count": 5,
          "DISK_GB": 5,
          "MEMORY_MB": 512,
          "VCPU": 2
      }
      "MIGRATION": {
          "consumer_count": 2,
          "DISK_GB": 5,
          "MEMORY_MB": 512,
          "VCPU": 2
      }
      "UNKNOWN": {
          "consumer_count": 1,
          "DISK_GB": 5,
          "MEMORY_MB": 512,
          "VCPU": 2
      }
    }
}

The new GET /usages response will look like this for a request of type GET /usages?project_id=<id>&user_id=<id>&consumer_type="INSTANCE" or GET /usages?project_id=<id>&consumer_type="INSTANCE" where the consumer_type key is specified:

{
    "usages": {
      "INSTANCE": {
          "consumer_count": 5,
          "DISK_GB": 5,
          "MEMORY_MB": 512,
          "VCPU": 2
      }
    }
}

A special request of the form GET /usages?project_id=<project id>&consumer_type=all will be allowed to enabled users to be able to query for the total count of all the consumers. The response for such a request will look like this:

{
  "usages": {
      "all": {
          "consumer_count": 3,
          "DISK_GB": 5,
          "MEMORY_MB": 512,
          "VCPU": 2
      }
  }
}

Note that consumer_type is an optional key for the GET /usages request.

The above REST API changes and the corresponding changes to the /reshaper REST API will be available from a new microversion.

Security impact

None.

Other end user impact

The external services using this feature like nova should take the responsibility of updating the consumer type of existing consumers from “UNKNOWN” to the actual type through the PUT /allocations/{consumer_uuid} REST API.

Performance Impact

None.

Other deployer impact

None.

Developer impact

None.

Upgrade impact

The placement-manage db sync command has to be run by the operators in order to upgrade the database schema to accommodate the new changes.

Implementation

Assignee(s)

Primary assignee:

<tssurya>

Other contributors:

<None>

Work Items

  • Add the new consumer_types table and create a new consumer_type_id column in the consumers table with a foreign key constraint to the id column of the consumer_types table.

  • Make the REST API changes in a new microversion for:

    • POST /allocations,

    • PUT /allocations/{consumer_uuid},

    • GET /allocations/{consumer_uuid},

    • GET /usages and

    • /reshaper

Dependencies

None.

Testing

Unit and functional tests to validate the feature will be added.

Documentation Impact

The placement API reference will be updated to reflect the new changes.

References

History

Revisions

Release Name

Description

Train

Introduced

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