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This article explains how CLAMP Control Loop Runtime is implemented.

Terminology

• Broadcast message: a message for all participants (participantId=null and participantType=null)
• Message to a participant: a message only for a participant (participantId and participantType properly filled).
• ThreadPoolExecutor: ThreadPoolExecutor executes the given task, into SupervisionAspect class is configured to execute tasks in ordered manner, one by one.
• Spring Scheduling: into SupervisionAspect class, the the @Scheduled annotation invokes "schedule()" method every "runtime.participantParameters.heartBeatMs" milliseconds with a fixed delay
• MessageIntercept: "@MessageIntercept" annotation is used into SupervisionHandler class to intercept "handleParticipantMessage" method calls using spring aspect oriented programming. In details is used to into SupervisionHandler class to intercept "handleParticipantMessage" methods.

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• GUI: graphical user interface, Postman or a Front-End Application

Design of Rest Api

Create of a Control Loop Type

• GUI calls POST "/commission" endpoint with a Control Loop Type Definition (Tosca Service Template) as body
• CL-runtime receives the call by Rest-Api (CommissioningController)
• It saves to DB the Tosca Service Template using PolicyModelsProvider
• if there are participants registered, it triggers the execution to send a broadcast PARTICIPANT_UPDATE message
• the message is built by ParticipantUpdatePublisher using Tosca Service Template data (to fill the list of ParticipantDefinition).

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Delete of a Control Loop Type

• GUI calls DELETE "/commission" endpoint
• CL-runtime receives the call by Rest-Api (CommissioningController)
• if there are participants registered, it CL-runtime triggers the execution to send a broadcast PARTICIPANT_UPDATE message
• the message is built by ParticipantUpdatePublisher with a an empty list of ParticipantDefinition
• It deletes the Control Loop Type from DB

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Create of a Control Loop

• GUI calls POST "/instantiation" endpoint with a Control Loop as body
• CL-runtime receives the call by Rest-Api (InstantiationController)
• It validates the Control Loop
• It saves the Control Loop to DB

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Update of a Control Loop

• GUI calls PUT "/instantiation" endpoint with a Control Loop as body
• CL-runtime receives the call by Rest-Api (InstantiationController)
• It validates the Control Loop
• It saves the Control Loop to DB

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Delete of a Control Loop

• GUI calls DELETE "/instantiation" endpoint
• CL-runtime receives the call by Rest-Api (InstantiationController)
• It checks that Control Loop is in UNINITIALISED status
• It deletes the Control Loop from DB

Design of

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"issues control loop commands to control loops

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"

UNINITIALISED to PASSIVE

• GUI calls "/instantiation/command" endpoint with PASSIVE as orderedState
• CL-runtime checks if participants registered are matching with the list of control Loop Element
• It updates control loop and control loop elements to DB (orderedState = PASSIVE)
• It validates the status order issued
• It triggers the execution to send a broadcast CONTROL_LOOP_UPDATE message
• the message is built by ControlLoopUpdatePublisher using Tosca Service Template data and ControlLoop data. (with startPhase = 0)
• It updates control loop and control loop elements to DB (state = UNINITIALISED2PASSIVE)

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PASSIVE to UNINITIALISED

• GUI calls "/instantiation/command" endpoint with UNINITIALISED as orderedState
• CL-runtime checks if participants registered are matching with the list of control Loop Element
• It updates control loop and control loop elements to DB (orderedState = UNINITIALISED)
• It validates the status order issued
• It triggers the execution to send a broadcast CONTROL_LOOP_STATE_CHANGE message
• the message is built by ControlLoopStateChangePublisher with controlLoopId
• It updates control loop and control loop elements to DB (state = PASSIVE2UNINITIALISED)

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PASSIVE to RUNNING

• GUI calls "/instantiation/command" endpoint with RUNNING as orderedState
• CL-runtime checks if participants registered are matching with the list of control Loop Element.
• It updates control loop and control loop elements to DB (orderedState = RUNNING)
• It validates the status order issued
• It triggers the execution to send a broadcast CONTROL_LOOP_STATE_CHANGE message
• the message is built by ControlLoopStateChangePublisher with controlLoopId
• It updates control loop and control loop elements to DB (state = PASSIVE2RUNNING)

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RUNNING to PASSIVE

• GUI calls "/instantiation/command" endpoint with UNINITIALISED as orderedState
• CL-runtime checks if participants registered are matching with the list of control Loop Element.
• It updates control loop and control loop elements to db (orderedState = RUNNING)
• It validates the status order issued
• It triggers the execution to send a broadcast CONTROL_LOOP_STATE_CHANGE message
• the message is built by ControlLoopStateChangePublisher with controlLoopId
• It updates control loop and control loop elements to db (state = RUNNING2PASSIVE)

StartPhase

The startPhase is particularly important in control loop update and control loop state changes because sometime the user wishes to control the order in which the state changes in Control Loop Elements in a control loop.

How to define StartPhase

StartPhase is defined as shown below in the Definition of TOSCA fundamental Control Loop Types yaml file.

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    org.onap.domain.database.Http_PMSHMicroserviceControlLoopElement:
      # Consul http config for PMSH.
      version: 1.2.3
      type: org.onap.policy.clamp.controlloop.HttpControlLoopElement
      type_version: 1.0.1
      description: Control loop element for the http requests of PMSH microservice
      properties:
        provider: ONAP
        participant_id:
          name: HttpParticipant0
          version: 1.0.0
        participantType:
          name: org.onap.k8s.controlloop.HttpControlLoopParticipant
          version: 2.3.4
        uninitializedToPassiveTimeout: 180
        startPhase: 1

How StartPhase works

In state changes from UNITITIALISED → PASSIVE, control loop elements are started in increasing order of their startPhase.

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In that scenario the message CONTROL_LOOP_UPDATE has been sent two times.

Design of

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managing messages

PARTICIPANT_REGISTER

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• A Participant participant starts and send a PARTICIPANT_REGISTER message
• ParticipantRegisterListener collects the message from DMaap
• if not present, it saves participant reference with status UNKNOWN to DB
• if is present a Control Loop Type, it triggers the execution to send a PARTICIPANT_UPDATE message to the participant registered (message of Priming).
• the message is built by ParticipantUpdatePublisher using Tosca Service Template data (to fill the list of ParticipantDefinition).
• It triggers the execution to send a PARTICIPANT_REGISTER_ACK message to the participant registered
• MessageIntercept intercepts that event, if PARTICIPANT_UPDATE message has been sent, it will be add a task to handle PARTICIPANT_REGISTER in SupervisionScanner
• SupervisionScanner starts the monitoring for participantUpdate

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PARTICIPANT_UPDATE_ACK

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• Participants A participant sends PARTICIPANT_UPDATE_ACK messages message in response to a PARTICIPANT_UPDATE message
• ParticipantUpdateAckListener collects the message from DMaap
• MessageIntercept intercepts that event and adds a task to handle PARTICIPANT_UPDATE_ACK in SupervisionScanner
• SupervisionScanner removes the monitoring for participantUpdate
• It updates the status of the participant to DB

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PARTICIPANT_STATUS

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• A participant sends a scheduled PARTICIPANT_STATUS message
• ParticipantStatusListener collects the message from DMaap
• MessageIntercept intercepts that event and adds a task to handle PARTICIPANT_STATUS in SupervisionScanner
• SupervisionScanner clears and starts the monitoring for participantStatus

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CONTROLLOOP_UPDATE_ACK

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• Participants A participant sends CONTROLLOOP_UPDATE_ACK messages message in response to a CONTROLLOOP_UPDATE  message. It will send a CONTROLLOOP_UPDATE_ACK for each CL-elements moved to the ordered state as indicated by the CONTROLLOOP_UPDATE.
• ControlLoopUpdateAckListener collects the message from DMaap
• It checks the status of all control loop elements and checks if the control loop is primed
• It updates the CL to DB if it is changed
• MessageIntercept intercepts that event and adds a task to handle a monitoring execution in SupervisionScanner

CONTROLLOOP_STATECHANGE_ACK

Design of a CONTROLLOOP_STATECHANGE_ACK is similar to the design for CONTROLLOOP_UPDATE_ACK

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Monitoring is designed to process the follow operations:

• to determinate of determine the next startPhase in a CONTROLLOOP_UPDATE message. 
• to upgrade update CL state: in a scenario that CL state are in "ControlLoop.state" is in a kind of transitional state (example UNINITIALISED2PASSIVE), if all CL-elements are moved properly to the specific state, the CL "ControlLoop.state" will be upgrade updated to that .and saved to DB
• to retry CONTROLLOOP_UPDATE/CONTROL_LOOP_STATE_CHANGE messages. if there is a CL Element not in the proper state, it will retry a broadcast message.
• to retry PARTICIPANT_UPDATE message to the participant in a scenario that CL-runtime do not receive PARTICIPANT_UPDATE_ACT from it.
• to send PARTICIPANT_STATUS_REQ to the participant in a scenario that CL-runtime do not receive PARTICIPANT_STATUS from it,

The solution Design of retry, timeout, and reporting for all Participant message dialogues are implemented into the monitoring execution.

• Spring Scheduling inserts the task to monitor retry execution into ThreadPoolExecutor
• ThreadPoolExecutor executes the task
• a message will be retry if CL-runtime do no receive Act message before MaxWaitMs milliseconds

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Design of Exception handling

GlobalControllerExceptionHandler

If error occurred during the Rest Api call, CL-runtime responses with a proper status error code and a JSON message error. This class is implemented to intercept and handle ControlLoopException, PfModelException and PfModelRuntimeException if they are thrown during the Rest Ali calls.

All of those classes must implement ErrorResponseInfo that contains message error and status response code. So the Exception is converted in JSON message.

RuntimeErrorController

If wrong end-point is called or an Exception not intercepted by GlobalControllerExceptionHandler, CL-runtime responses with a proper status error code and a JSON message error.
This class is implemented to redirect the standard Web error page to a JSON message error.
Typically that happen when a wrong end-point is called, but also could be happen for not authorized call, or any other Exception not intercepted by GlobalControllerExceptionHandler.

Handle version and "X-ONAP-RequestID"

RequestResponseLoggingFilter class handles version and "X-ONAP-RequestID" during a Rest-Api call; it works as a filter, so intercepts the Rest-Api and adds to the header those information.

Media Type Support

CL-runtime Rest Api supports application/json, application/yaml and text/plain Media Types. The configuration is implemented in CoderHttpMesageConverter.

application/json

JSON format is a standard for Rest Api. For the conversion from JSON to Object and vice-versa will be used org.onap.policy.common.utils.coder.StandardCoder.

application/yaml

YAML format is a standard for Control Loop Type Definition. For the conversion from YAML to Object and vice-versa will be used org.onap.policy.common.utils.coder.StandardYamlCoder.

text/plain

Text format is used by Prometheus. For the conversion from Object to String  will be used StringHttpMessageConverter.

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