tacker/doc/source/user/placement_policy_usage_guide.rst

VDU Placement policy

OpenStack nova server groups can be used to control the affinity and anti-affinity scheduling policy for a group of VDU's. Below placement policies are supported:

Affinity:
    The policy that forces Nova to hosts the concerned VDUs in a same
    hypervisor.

Anti-Affinity:
    The policy that forces Nova to hosts the concerned VDUs each
    in a different hypervisor.

Soft-Affinity:
    The policy that forces nova about if it is not possible to
    schedule some VDUs to the same host then the subsequent VDUs will be
    scheduled together on another host. In this way operator can express a
    good-to-have relationship between a group of VDUs.

Soft-Anti-Affinity:
    The policy that forces nova about if it is not
    possible to schedule VDUs on different hosts then VDUs might get
    scheduled on a same host where another VDUs are running from the same
    group.

TOSCA schema for placement policy

Tacker defines TOSCA schema for the placement policy as given below:

tosca.policies.tacker.Placement:
  derived_from: tosca.policies.Placement
  description: Defines policy for placement of VDU's.
  properties:
    policy:
      type: string
      required: false
      default: affinity
      constraints:
        - valid_values: [ affinity, anti-affinity ]
      description: Placement policy for target VDU's.
    strict:
      type: boolean
      required: false
      default: true
      description: If the policy is not mandatory, set this flag to
      'false'. Setting this flag to 'false' allows the VDU deployment
      request to continue even if the nova-scheduler fails to assign
      compute hosts under the policy.
  targets:
      type: list
      entry_schema:
        type: string
      required: true
      description: List of VDU's on which placement policy will be applied.

Sample TOSCA with placement policy

Following TOSCA snippet shows the placement policy used in VNFD, in which vdu1 and vdu2 are already defined VDUs.

Affinity policy

policies:
   - my_compute_placement_policy:
       type: tosca.policies.tacker.Placement
       properties:
         policy: affinity
         strict: true
       description: Apply my placement policy to my applications servers
       targets: [ VDU1, VDU2 ]

Anti-Affinity policy

policies:
   - my_compute_placement_policy:
       type: tosca.policies.tacker.Placement
       properties:
         policy: anti-affinity
         strict: true
       description: Apply my placement policy to my applications servers
       targets: [ VDU1, VDU2 ]

Soft-Affinity policy

policies:
   - my_compute_placement_policy:
       type: tosca.policies.tacker.Placement
       properties:
         policy: affinity
         strict: false
       description: Apply my placement policy to my applications servers
       targets: [ VDU1, VDU2 ]

Soft-Anti-Affinity policy

policies:
   - my_compute_placement_policy:
       type: tosca.policies.tacker.Placement
       properties:
         policy: anti-affinity
         strict: false
       description: Apply my placement policy to my applications servers
       targets: [ VDU1, VDU2 ]

The soft flag defines the softness of the placement policy.

Deploying placement TOSCA template using Tacker

Once OpenStack/Devstack along with Tacker has been successfully installed, deploy a sample placement policy template from location given below: https://opendev.org/openstack/tacker/src/branch/master/samples/tosca-templates/vnfd/tosca-placement-policy-anti-affinity.yaml

Refer the 'Getting Started' link below on how to create a VNFD and deploy a VNF: https://docs.openstack.org/tacker/latest/install/getting_started.html