Policy Types

Concept

A Policy Type is an abstract specification of the rules to be checked and/or enforced when an Action is performed on a cluster that contains nodes of certain Profile Type.

A registry of policy types is built in memory when the Senlin engine (senlin-engine) is started. In future, Senlin will allow users to provide additional policy type implementations as plug-ins to be loaded dynamically.

A policy type implementation dictates which fields are required, which fields are optional and sometimes the constraints on field values. When a Policy is created by referencing this policy type, the fields are assigned with concrete values. For example, a policy type senlin.policy.deletion conceptually specifies the properties required:

criteria: String # valid values - OLDEST_FIRST, YOUNGEST_FIRST, RANDOM
destroy_after_deletion: Boolean
grace_period: Integer
reduce_desired_capacity: Boolean

The specification of a policy object of this policy type may look like following:

type: senlin.policy.deletion
version: 1.0
properties:
  criteria: OLDEST_FIRST
  destroy_after_deletion: True
  grace_period: 120
  reduce_desired_capacity: True

Listing Policy Types

Senlin server comes with some built-in policy types. You can check the list of policy types using the following command:

$ openstack cluster policy type list
+--------------------------------+---------+----------------------------+
| name                           | version | support_status             |
+--------------------------------+---------+----------------------------+
| senlin.policy.affinity         | 1.0     | SUPPORTED since 2016.10    |
| senlin.policy.batch            | 1.0     | EXPERIMENTAL since 2017.02 |
| senlin.policy.deletion         | 1.0     | SUPPORTED since 2016.04    |
| senlin.policy.deletion         | 1.1     | SUPPORTED since 2018.01    |
| senlin.policy.health           | 1.0     | EXPERIMENTAL since 2017.02 |
| senlin.policy.loadbalance      | 1.0     | SUPPORTED since 2016.04    |
| senlin.policy.loadbalance      | 1.1     | SUPPORTED since 2018.01    |
| senlin.policy.region_placement | 1.0     | EXPERIMENTAL since 2016.04 |
|                                |         | SUPPORTED since 2016.10    |
| senlin.policy.scaling          | 1.0     | SUPPORTED since 2016.04    |
| senlin.policy.zone_placement   | 1.0     | EXPERIMENTAL since 2016.04 |
|                                |         | SUPPORTED since 2016.10    |
+--------------------------------+---------+----------------------------+

The output is a list of policy types supported by the Senlin server.

Showing Policy Details

Each Policy Type has a schema for its spec (i.e. specification) that describes the names and types of the properties that can be accepted. To show the schema of a specific policy type along with other properties, you can use the following command:

$ openstack cluster policy type show senlin.policy.deletion-1.1
support_status:
  '1.0':
  - since: '2016.04'
    status: SUPPORTED
  '1.1':
  - since: '2018.01'
    status: SUPPORTED
id: senlin.policy.deletion-1.1
location: null
name: senlin.policy.deletion-1.1
schema:
  criteria:
    constraints:
    - constraint:
      - OLDEST_FIRST
      - OLDEST_PROFILE_FIRST
      - YOUNGEST_FIRST
      - RANDOM
      type: AllowedValues
    default: RANDOM
    description: Criteria used in selecting candidates for deletion
    required: false
    type: String
    updatable: false
  destroy_after_deletion:
    default: true
    description: Whether a node should be completely destroyed after deletion. Default
      to True
    required: false
    type: Boolean
    updatable: false
  grace_period:
    default: 0
    description: Number of seconds before real deletion happens.
    required: false
    type: Integer
    updatable: false
  hooks:
    default: {}
    description: Lifecycle hook properties
    required: false
    schema:
      params:
        default: {}
        required: false
        schema:
          queue:
            default: ''
            description: Zaqar queue to receive lifecycle hook message
            required: false
            type: String
            updatable: false
          url:
            default: ''
            description: Url sink to which to send lifecycle hook message
            required: false
            type: String
            updatable: false
        type: Map
        updatable: false
      timeout:
        default: 0
        description: Number of seconds before actual deletion happens.
        required: false
        type: Integer
        updatable: false
      type:
        constraints:
        - constraint:
          - zaqar
          - webhook
          type: AllowedValues
        default: zaqar
        description: Type of lifecycle hook
        required: false
        type: String
        updatable: false
    type: Map
    updatable: false
  reduce_desired_capacity:
    default: true
    description: Whether the desired capacity of the cluster should be reduced along
      the deletion. Default to True.
    required: false
    type: Boolean
    updatable: false

Here, each property has the following attributes:

  • default: the default value for a property when not explicitly specified;

  • description: a textual description of the use of a property;

  • required: whether the property must be specified. Such kind of a property usually doesn’t have a default value;

  • type: one of String, Integer, Boolean, Map or List;

  • updatable: a boolean indicating whether a property is updatable.

The default output from the policy-type-show command is in YAML format. You can choose to show the spec schema in JSON format by specifying the -f json option as shown below:

$ openstack cluster policy type show -f json senlin.policy.deletion-1.0

For information on how to manage the relationship between a policy and a cluster, please refer to Cluster-Policy Bindings.

See Also

Check the list below for documents related to the creation and usage of Policy objects.