A Control Loop Type is defined in a TOSCA service template. A TOSCA Service Template has two parts: a definition part in the service template itself, which contains the definitions of concepts that can be used to define the types of concepts that can appear on a Toplogy Template and a Topology Template that defines a topology. See the Oasis Open TOSCA web page for more details on TOSCA.

Unsurprisingly, to define a Control Loop Type in TOSCA, we must first define a number of Control Loop related concepts that we can use in all control loops .

Fundamental TOSCA Concepts for Control Loops

The following TOSCA concepts are the fundamental concepts in a TOSCA Service Template for defining control loops.

exist. They are described in Section 1. Section 2 describes how properties are managed. Properties are the configuration parameters that are provided to Control Loops and the Control Loop Elements they use. Section 3 describes how to define a Control Loop using the predefined Control Loop concepts.

1 Standard TOSCA Service Template Concepts for Control Loops

These concepts are the base concepts available to users who write definitions for control loops in TOSCA. TOSCA control loop definitions are written using these concepts.

1.1 Fundamental TOSCA Concepts for Control Loops

The following TOSCA concepts are the fundamental concepts in a TOSCA Service Template for defining control loops.

The TOSCA concepts above may be declared in the TOSCA Service Template of a control loop. If the concepts already exist in the Design Time Catalogue or the Runtime Inventory, they may be omitted from a TOSCA service template that defines a control loop type.

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The Yaml file that holds the  Definition of TOSCA fundamental Control Loop Types is available in Github and is the canonical definition of the Control Loop concepts.

Property: Metadata defined in TOSCA that is associated with a Control Loop, a Control Loop Element, or a Participant.

TOSCA Property Type: The TOSCA defintion of the type of a property. A property can have a generic type such as string or integer or can have a user defined TOSCA data type.

TOSCA Property Value: The value of a Property Type. Property values are assigned at run time in CLAMP.

Common Property Type: Property Types that apply to all instances of a Control Loop Type.

Common Property Value: The value of a Property Type. It is assigned at run time once for all instances of a Control Loop Type.

Instance Specific Property Type: Property Types that apply to an individual instance of a Control Loop Type.

Instance Specific Property Value: The value of a Property Type that applies to an individual instance of a Control Loop Type. The value is assigned at run time for each control loop instance.

is made up of several components, those which represent applications, those which represent dynamic config schemas, and the actual node_templates which makes up the loop itself.

Applications can be a DCAE microservice, an operational policy, or any other application as long as it can be modeled, and the targeted ecosystem to has a participant client waiting for the event distributions from CLAMP via DMaaP Message Router.

Dynamic config on the other hand can be a monitoring policy, or any other resource that provides config to parts of the loop, can be updated after the run time phase has started and is supported by the components hosting the applications in the control loop.

1. Control Loop TOSCA file definition

1.1 Control Loop Component Definition 

A Control Loop Component that can be part of a control loop, it defines the components that partake in a control loop, and are implemented at run time by participants. The control loop component definition is truly dynamic and, as long as the participant that the control loop component definition relates to understands its definition, it can be anything. However, we have designed a base control loop component attribute that's generic and that can act as a good starting point.

node_types:
  org.onap.CL_Component:
    properties:
      component_name:
        type: string
        description: Human readable name for the component.
        required: true
      provider:
        type: string
        description: Provider of the component and of the descriptor.
        required: true
      component_version:
        type: string
        description: Software version of the component.
        required: true
      resource_id:
        type: string
        description: >The ID of the resource, 
          should be provided if the resource was uploaded to the entity's inventory already.
        required: false
      resource_content:
        type: string
        description: the contents of the component resource, to be uploaded during commssioning phase of loop.
        required: false
      monitoring_policy:
        type: string
        description: A reference to the monitoring policy if applicable.
        required: false
    version: 0.0.1
    derived_from: tosca.nodes.Root

1.2 Loop Definition

The loop definition is explicit in the node_templates within the topology_template,  a Control Loop node template is specified and any node tempalte specified in the Control Loop node tepolcate is part of the control loop managed by CLAMP.

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1.2 TOSCA Concepts for Control Loop Elements delivered by ONAP

1.2.1 Policy Control Loop Element

The Policy Participant runs Policy Control Loop Elements. Each Policy Control Loop Element manages the deployment of the policy specified in the Policy Control Loop Element definition. The Yaml file that holds the  Policy Control Loop Element Type definition is available in Github and is the canonical definition of the Policy Control Loop Element type. For a description of the Policy Control Loop Element and Policy Participant, please see The CLAMP Policy Framework Participant page.

1.2.2 HTTP Control Loop Element

The HTTP Participant runs HTTP Control Loop Elements. Each HTTP Control Loop Element manages REST communication towards a REST endpoint using the REST calls a user has specified in the configuration of the HTTP Control Loop Element. The Yaml file that holds the  HTTP Control Loop Element Type definition is available in Github and is the canonical definition of the HTTP Control Loop Element type. For a description of the HTTP Control Loop Element and HTTP Participant, please see The CLAMP HTTP Participant page.

1.2.3 Kubernetes Control Loop Element

The Kubernetes Participant runs Kubernetes Control Loop Elements. Each Kubernetes Control Loop Element manages a Kubernetes microservice using Helm. The user defines the Helm chart for the Kubernetes microservice as well as other properties that the microservice requires in order to execute. The Yaml file that holds the Kubernetes Control Loop Element Type defintion is available in Github and is the canonical definition of the Kubernetes Control Loop Element type. For a description of the Kubernetes Control Loop Element and Kubernetes Participant, please see The CLAMP Kubernetes Participant page.

2 Common and Instance Specific Properties

Properties are used to define the configuration for Control Loops and Control Loop Elements. At design time, the types, constraints, and descriptions of the properties are specified. The values for properties are specified in the CLAMP GUI at runtime. TOSCA provides support for defining properties, see Section 3.6.10: TOSCA Property Definition in the TOSCA documentation.

2.1 Terminology for Properties

Property: Metadata defined in TOSCA that is associated with a Control Loop, a Control Loop Element, or a Participant.

TOSCA Property Type: The TOSCA definition of the type of a property. A property can have a generic type such as string or integer or can have a user defined TOSCA data type.

TOSCA Property Value: The value of a Property Type. Property values are assigned at run time in CLAMP.

Common Property Type: Property Types that apply to all instances of a Control Loop Type.

Common Property Value: The value of a Property Type. It is assigned at run time once for all instances of a Control Loop Type.

Instance Specific Property Type: Property Types that apply to an individual instance of a Control Loop Type.

Instance Specific Property Value: The value of a Property Type that applies to an individual instance of a Control Loop Type. The value is assigned at run time for each control loop instance.

Control Loop Properties can be common or instance specific. See Section 2 of TOSCA Defined Control Loops: Architecture and Design for a detailed description of the usage of common and instance specific properties.

2.2 Common Properties

Common properties apply to all instances of a control loop. Common properties are identified by a special metadata flag in Control Loop and Control Loop Element definitions. For example, the startPhase parameter on any Control Loop Element has the same value for any instance of that control loop element, so it is defined as shown below in the Definition of TOSCA fundamental Control Loop Types yaml file.

startPhase:
  type: integer
  required: false
  constraints:
  - greater-or-equal: 0
  description: A value indicating the start phase in which this control loop element will be started, the
               first start phase is zero. Control Loop Elements are started in their start_phase order and stopped
               in reverse start phase order. Control Loop Elements with the same start phase are started and
               stopped simultaneously
  metadata:
    common: true

The "common: true" value in the metadata of the startPhase property identifies that property as being a common property. This property will be set on the CLAMP GUI during control loop commissioning.

2.3 Instance Specific Properties

Instance Specific  properties apply to individual instances of a Control Loop and/or Control Loop Element and must be set individually for Control Loop and Control Loop Element instance. Properties are instance specific by default, but can be identified by a special metadata flag in Control Loop and Control Loop Element definitions. For example, the chart parameter on a Kubernetes Control Loop Element has a different value for every instance of a Kubernetes Control Loop Element, so it can be defined as shown below in the  Kubernetes Control Loop Type definition yaml file.

# Definition that omits the common flag metadata
chart:
  type: org.onap.datatypes.policy.clamp.controlloop.kubernetesControlLoopElement.Chart
  typeVersion: 1.0.0
  description: The helm chart for the microservice
  required: true

# Definition that specifies the common flag metadata
chart:
  type: org.onap.datatypes.policy.clamp.controlloop.kubernetesControlLoopElement.Chart
  typeVersion: 1.0.0
  description: The helm chart for the microservice
  required: true
  metadata:
    common: false

The "common: false" value in the metadata of the chart property identifies that property as being an instance specific property. This property will be set on the CLAMP GUI during control loop instantiation.

3. Writing a Control Loop Type Definition

The TOSCA definition of a control loop contains a TOSCA Node Template for the control loop itself, which contains TOSCA Node Templates for each Control Loop Element that makes up the Control Loop.

To create a control loop, a user creates a TOSCA Topology Template. In the Topology Template, the user creates a TOSCA Node Template for each Control Loop Element that will be in the Control Loop Definition. Finally, the user creates the Node Template that defines the Control Loop itself, and references the Control Loop Element definitions that make up the Control Loop Definition.

3.1 The Gentle Guidance Control Loop

The best way to explain how to create a Control Loop Definition is by example.

The example Gentle Guidance control loop is illustrated in the diagram above. The domain logic for the control loop is implemented in a microservice running in Kubernetes, a policy, and some configuration that is passed to the microservice over a REST endpoint. We want to manage the life cycle of the domain logic for our Gentle Guidance control loop using our TOSCA based Control Loop Life Cycle Management approach. To do this we create four Control Loop Element definitions, one for the Kubernetes microservice, one for the policy and one or the REST configuration.

3.2 The TOSCA Control Loop Definition

We use a TOSCA Topology Template to specify a Control Loop definition and the definitions of its Control Loop Elements. Optionally, we can specify default parameter values in the TOSCA Topology Template. The actual values of Control Loop common and instance specific parameters are set at run time in the CLAMP GUI.

In the case of the Gentle Guidance control loop, we define a Control Loop Element Node Template for each part of the domain logic we are managing. We then define the Control Loop Node Template for the control loop itself.

The code fragment below shows the TOSCA Topology Template for the Gentle Guidance domain when no parameters are defined. Please refer to the Yaml file in Github for the definitive Yaml specification. 

tosca_definitions_version: tosca_simple_yaml_1_3
topology_template:
  node_templates:
    org.onap.domain.gentleguidance.KubernetesControlLoopElementDefinition:
      version: 1.0.0
      type: org.onap.policy.clamp.controlloop.KubernetesControlLoopElement
      type_version: 1.0.1
      description: Control loop element for the Gentle Guidance Kubernetes Microservice
    org.onap.domain.gentleguidance.RestControlLoopElementDefinition:
      version: 1.0.0
      type: org.onap.policy.clamp.controlloop.HttpControlLoopElement
      type_version: 1.0.1
      description: Control loop element for the Gentle Guidance Microservice REST configuration
    org.onap.domain.gentleguidance.PolicyControlLoopElementDefinition:
      version: 1.0.0
      type: org.onap.policy.clamp.controlloop.Participant:PolicyControlLoopElement
      type_version: 1.0.1
    derived_from: tosca.nodetypes.Root
      propertiesdescription: Control loop element for the Gentle provider:Guidance Operational Policy
 blueprint
    typeorg.onap.domain.gentleguidance.ControlLoopDefinition:
string      version: 1.0.0
   requred: false  type: org.onap.policy.clamp.controlloop.ControlLoopElement:ControlLoop
      type_version: 1.0.1
      derived_from: tosca.nodetypes.Root
    properties:description: Control loop definition for the Gentle Guidance domain
      providerproperties:
        typeelements:
string         requred: false- org.onap.domain.gentleguidance.KubernetesControlLoopElementDefinition:1.0.0
         participant_id:- org.onap.domain.gentleguidance.RestControlLoopElementDefinition:1.0.0
         type: onap.datatypes.ToscaConceptIdentifier
        requred: true
  org.onap.policy.clamp.controlloop.ControlLoop:
    version: 1.0.1
    derived_from: tosca.nodetypes.Root
    properties:
      provider:
        type: string- org.onap.domain.gentleguidance.PolicyControlLoopElementDefinition:1.0.0

The code fragment below shows the TOSCA Topology Template for the Gentle Guidance domain when the default values of  parameters are defined. Please refer to the Yaml file in Github for the definitive Yaml specification.

tosca_definitions_version: tosca_simple_yaml_1_3
topology_template:
  node_templates:
    org.onap.domain.gentleguidance.KubernetesControlLoopElementDefinition:
        requredversion: false1.0.0
      elementstype:  org.onap.policy.clamp.controlloop.KubernetesControlLoopElement
      type_version: list1.0.1
        requireddescription: trueControl loop element for the Gentle Guidance Kubernetes Microservice
entry_schema:      properties:
    type: onap.datatypes.ToscaConceptIdentifier   org.onap.policy.clamp.controlloop.DCAEMicroserviceControlLoopElementprovider:  Ericsson
  version: 1.0.1     derived_fromparticipantType: org.onap.policy.clamp.controlloop.ControlLoopElement
    properties:.controlloop.participant.Kubernetes:1.0.0
        dcae_blueprint_id:startPhase: 2
        typeuninitializedToPassiveTimeout: onap.datatypes.ToscaConceptIdentifier180
        requredchart:
true   org.onap.policy.clamp.controlloop.PolicyTypeControlLoopElement:     version: 1.0.1     derived_from: org.onap.policy.clamp.controlloop.ControlLoopElement
    properties:chartId: GentleGuidance:1.0.0
       policy_type_id:     releaseName: Istanbul
  type: onap.datatypes.ToscaConceptIdentifier         requred: truenamespace: org.onap.policy.controlloop.gentleguidance
    org.onap.policydomain.clampgentleguidance.controlloop.CDSControlLoopElementRestControlLoopElementDefinition:
      version: 1.0.10
      derived_fromtype: org.onap.policy.clamp.controlloop.ControlLoopElement.HttpControlLoopElement
      type_version: 1.0.1
      propertiesdescription: Control loop element for the Gentle  cds_blueprint_id:
 Guidance Microservice REST configuration
      typeproperties: onap.datatypes.ToscaConceptIdentifier
        provider: Ericsson
   requred: true topology_template:   node_templatesparticipantType: org.onap.policy.controlloop.participant.Http:1.0.0
   org.onap.dcae.controlloop.DCAEMicroserviceControlLoopParticipant:     startPhase: 1
version: 2.3.4       typebaseUrl: org.onap.policy.clamp.controlloop.Participant
https://10.10.10.10:12345/gentleguidancemicroservice
     type_version: 1.0.1  httpHeaders:
    description: Participant for DCAE microservices  "Content-Type": "application/json"
   properties:         provider"Accept": ONAP"application/json"
    org.onap.policy.controlloop.MonitoringPolicyControlLoopParticipant:    configurationEntities:
  version: 2.3.1       type: org.onap.policy.clampcontrolloop.controlloop.Participant
      type_version: gentleguidance.setGentleGuidanceConfig:1.0.1
   0:
  description: Participant for DCAE microservices       properties:
 configurationEntityId: org.onap.policy.controlloop.gentleguidance.setGentleGuidanceConfig:1.0.0
      provider: ONAP     org.onap.policy.controlloop.OperationalPolicyControlLoopParticipantrestSequence:
      version: 3.2.1     -  typerestRequestId: org.onap.policy.clamp.controlloop.Participant.controlloop.gentleguidance.setGentleGuidanceConfig.CreateGentle:1.0.0
      type_version: 1.0.1       descriptionhttpMethd: ParticipantPOST
for DCAE microservices       properties:     path: "gentle/create"
  provider: ONAP     org.onap.ccsdk.cds.controlloop.CdsControlLoopParticipant:       versionbody:
2.2.1       type: org.onap.policy.clamp.controlloop.Participant       type_version gentleLevel: 1.0.1veryGentle
      description: Participant for DCAE microservices      gentleType: properties:softAndFurry
        provider: ONAP     org.onap.domain.pmsh.PMSH_DCAEMicroserviceexpectedResponse: 200
     version: 1.2.3      - typerestRequestId: org.onap.policy.clamp.controlloop.DCAEMicroserviceControlLoopElement.controlloop.gentleguidance.setGentleGuidanceConfig.CreateGuidance:1.0.0
              type_versionhttpMethd: 1.0.0 POST
         description: Control loop element for the DCAE microservice for Performance Management Subscription Handlingpath: "guidance/create"
            properties:  body:
      provider: Ericsson         participant_idguidanceLevel: high
          name: org.onap.dcae.controlloop.DCAEMicroserviceControlLoopParticipant     guidanceType: subtle
    version: 2.3.4         dcae_blueprint_idexpectedResponse: 200
         name: org.onap.dcae.blueprints.PMSHBlueprint.policy.controlloop.gentleguidance.updateGentleGuidanceConfig:1.0.0:
            versionconfigurationEntityId: org.onap.policy.controlloop.gentleguidance.updateGentleGuidanceConfig:1.0.0
            org.onap.domain.pmsh.PMSH_MonitoringPolicyControlLoopElementrestSequence:
      version: 1.2.3     -  typerestRequestId: org.onap.policy.controlloop.clampgentleguidance.controlloop.PolicyTypeControlLoopElement
      type_version: updateGentleGuidanceConfig.CreateGentle:1.0.0
      description: Control loop element for the monitoring policy for Performance Management Subscription HandlinghttpMethd: PUT
      properties:         providerpath: Ericsson
   "gentle/update]"
    participant_id:           namebody:
org.onap.policy.controlloop.PolicyControlLoopParticipant           version: 2.3.1    gentleLevel: robust
   policy_type_id:           name: onap.policies.monitoring.pm-subscription-handler
   gentleType: hardAndGritty
       version: 1.0.0     org.onap.domain.pmsh.PMSH_OperationalPolicyControlLoopElement expectedResponse: 200
     version: 1.2.3      - typerestRequestId: org.onap.policy.clampcontrolloop.gentleguidance.controlloop.PolicyTypeControlLoopElement
      type_version: updateGentleGuidanceConfig.CreateGuidance:1.0.0
      description: Control loop element for the operational policy forhttpMethd: PerformancePUT
Management Subscription Handling       properties:         provider: Ericssonpath: "guidance/update"
         participant_id:     body:
     name: org.onap.policy.controlloop.PolicyControlLoopParticipant          guidanceLevel: version: 2.3.1low
         policy_type_id:       guidanceType: terse
  name: onap.policies.operational.pm-subscription-handler           versionexpectedResponse: 1.0.0200
    org.onap.domain.pmsh.PMSH_CDS_ControlLoopElementgentleguidance.PolicyControlLoopElementDefinition:
      version: 1.20.30
      type: org.onap.policy.clamp.controlloop.ControlLoopElementPolicyControlLoopElement
      type_version: 1.0.01
      description: Control loop element for CDSthe forGentle PerformanceGuidance ManagementOperational Subscription HandlingPolicy
      properties:
       
provider: Ericsson         participant_Id:
          name: org.onap.ccsdk.cds.controlloop.CdsControlLoopParticipant   provider: Ericsson
      version  participantType: 3.2.1org.onap.policy.controlloop.participant.Policy:1.0.0
        cds_blueprint_idstartPhase: 0
         namepolicyType: org.onap.ccsdk.cds.PMSHCdsBlueprintonap.policies.controlloop.operational.common.Apex:1.0.0
           version: policyId: org.onap.domain.gentleguidance.policy.GentleGuidanceAssertive:1.0.0
    org.onap.domain.pmshgentleguidance.PMSHControlLoopDefinitionControlLoopDefinition:
      version: 1.20.30
      type: org.onap.policy.clamp.controlloop.ControlLoop
      type_version: 1.0.01
      description: Control loop definition for Performancethe ManagementGentle SubscriptionGuidance Handlingdomain
      properties:
        provider: Ericsson
  provider: Ericsson      elements:
        - org.onap.domain.gentleguidance.KubernetesControlLoopElementDefinition:1.0.0
         elements:- org.onap.domain.gentleguidance.RestControlLoopElementDefinition:1.0.0
        - name: org.onap.domain.pmsh.PMSH_DCAEMicroservice
          version: 1.2.3
        - name: org.onap.domain.pmsh.PMSH_MonitoringPolicyControlLoopElement
          version: 1.2.3
        - name: org.onap.domain.pmsh.PMSH_OperationalPolicyControlLoopElement
          version: 1.2.3
        - name: org.onap.domain.pmsh.PMSH_CDS_ControlLoopElement
          version: 1.2.3

2.2: Modelling from TOSCA to Commissioned Data in Run Time Inventory

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org.onap.domain.gentleguidance.PolicyControlLoopElementDefinition:1.0.0

4. Creating Custom Control Loop Elements

Any organization can include their own component in the framework and use the framework and have the Policy Framework CLAMP manage the lifecycle of domain logic in their component as part of a Control Loop. To do this, a participant for the component must be developed that allows Control Loop Elements for that component to be run. To develop a participant, the participant must comply with the CLAMP Participants framework and in particular comply with The CLAMP Automation Composition Participant Protocol. The organization must also specify a new Control Loop Element type definition in TOSCA similar to those supplied in ONAP and described in Section 1.2. This Control Loop Element type tells the CLAMP Control Loop Lifecycle management that the Control Loop Element exists and can be included in control loops. It also specifies the properties that can be specified for the Control Loop Element.

An organization can supply the code for the Participant (for example as a Java jar file) and a TOSCA artifact with the Control Loop Element definition and it can be added to the platform. In future releases, support will be provided to include participants and their Control Loop Element definitions as packaged plugins that can be installed on the platform.