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1. Most obviously, the framework must be capable of being triggered by an event or invoked, and making decisions at run time.
2. It must be deployment agnostic; capable of managing policies for various Policy Decision Points (PDPs) or policy engines.
3. It must be metadata driven, allowing policies to be deployed, modified, upgraded, and removed as the system executes.
4. It must provide a flexible template model driven policy design approach for template policy type programming and specification of policies.
5. It must be extensible, allowing straightforward integration of new PDPs, policy formats, and policy development environments.

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The PolicyDevelopment component implements the functionality for development of policy types and policies. PolicyAdministration is responsible for the deployment life cycle of policies as well as interworking with the mechanisms required to orchestrate the nodes and containers on which policies run. PolicyAdministration is also responsible for the administration of policies at run time; ensuring that policies are available to users, that policies are executing correctly, and that the state and status of policies is monitored. PolicyExecution is the set of PDPs running in the ONAP system and is responsible for making policy decisions and for managing the administrative state of the PDPs as directed by PolicyAdministration. 

PolicyDevelopment creates policy artifacts and supporting information in the policy database. PolicyAdministration reads those artifacts and the supporting information from the policy database whilst deploying policy artifacts. Once the policy artifacts are deployed, PolicyAdministration handles the run-time management of the PDPs on which the policies are running. PolicyDeveloment PolicyDevelopment interacts with ONAP design time components, and has no programmatic interface with PolicyAdministration, PolicyExecution or any other run-time ONAP components.

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PolicyDevelopment provides a CRUD API for policy types and policies. The policy types and policy artifacts and their metadata (Information about policies, policy templatestypes, and their interrelations ) are stored in the PolicyDB. The PolicyDevGUI, PolicyDistribution, and other applications such as Portal can use the PolicyDevelopment API to create, update, and delete policy templates types and policies.

PolicyAdministration has two important functions:

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The UML class diagram above shows the portion of the Policy Framework Object Model that applies to PolicyDeployment and PolicyExecution.

The UML class diagram above shows the portion of the Policy Framework Object Model that applies to PolicyDevelopment and PolicyDeployment.

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PolicyDevelopment provides the RESTful Policy Design API, which allows other components to query policy types and policy type implementations, to determine the model information, rules, or tasks that they require, to specialize policy flow, and to generate policies from policy types. This API is used by the ONAP Policy Framework and other components such as PolicyDistribution to create policies from policy types.

Consider a policy type created for managing faults on vCPE equipment in a vendor independent way. The policy type captures the generic logic required to manage the faults and specifies the vendor specific information that must be supplied to the template type for specific vendor vCPE VFs. The actual  vCPE policy that is used for managing particular vCPE equipment is created by setting the parameters specified in the policy type together with the specific modeled information, rules and tasks in the policy type implementation for that vendor model of vCPE.

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It is possible to generate policy types using MDD (Model Driven Development) techniques. Policy types are expressed using a DSL (Domain Specific Language) or a policy specification environment for a particular application domain. For example, policy types for specifying SLAs could be expressed in a SLA DSL and policy types for managing SON features could be generated from a visual SON management tool. The ONAP Policy framework provides an API that allows tool chains to create policy types. SDC uses this approach for generating Policy Types in the Policy Framework, see the Model driven Control Loop Design page.

The SDC GUI supports several types of policies that can be captured at design time. DCAE micro service configuration policies can be onboarded via the DCAE-DS (DCAE Design Studio).

The GUI implementation in another ONAP component such as SDC DCAE-DS uses the API_User API to create and edit ONAP policy types.

2.2.1.2 Programming Policy Type Implementations

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A more formal approach is preferred. For policy type implementations, programmers use a specific Eclipse project type for developing each type of implementation, a Policy Type Implementation SDK. The project is under source control in git. This Eclipse project is structured correctly for creating implementations for a specific type of PDP. It includes the correct POM files for generating the policy type implementation and has editors and perspectives that aid  programmers in their work.

2.2.2 Policy Design

The PolicyCreation function of PolicyDevelopment creates policies from a policy type.  The information expressed during policy type design is used to parameterize a policy type to create an executable policy. A service designer and/or operations team can use tooling that reads the TOSCA Policy Type specifications to express and capture a policy at its highest abstraction level. Alternatively, the parameter for the policy can be expressed in a raw JSON or YAML file and posted over the policy design API described on the Model driven Control Loop Design page.

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The sequence diagram below is a high level view of SDC-triggered concrete policy generation for some arbitrary entity EntityA. The parameters to create a policy are read from a TOSCA Policy specification read from a CSAR received from SDC.

PolicyDesign contains a uses the PolicyDistribution component PolicyDesignSDCHandler for managing SDC-triggered concrete triggered  policy creation and update requests. PolicyDesignSDCHandler PolicyDistribution is an API_User, it uses the Policy Design API to execution for policy creation and update. It reads the information it needs to populate the policy template type from a TOSCA specification in a CSAR received from SDC and then uses this information to automatically generate a policy.

Note that SDC provides a wrapper for the SDC API as a Java Client and also provides a TOSCA parser. See Policy Platform - SDC Service Distribution Software Architecture

In Step 4 above, the PolicyDesignSDCHandler the PolicyDesign must download the CSAR file. If the policy is to be composed from the TOSCA definition, it must also parse the TOSCA definition.

In Step 9 above, the PolicyDesignSDCHandler the PolicyDesign must send back/publish status events to SDC such as DOWNLOAD_OK, DOWNLOAD_ERROR, DEPOLYDEPLOY_OK, DEPOLYDEPLOY_ERROR, NOTIFIED.

2.2.2.

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4 Scripted Model Driven Policy Design

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The SDC GUI supports several types of policies that can be captured during design time. DCAE micro service configuration policies can be onboarded via the DCAE-DS (DCAE Design Studio).

The GUI implementation in another ONAP component such as SDC or the DCAE-DS uses the API_User API to create and edit ONAP policies. Note that this puts an impact on those components.

2.2.2.4 Scripted Model Driven Policy Design

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Service policies such as optimization and placement policies can be specified as a TOSCA Policy at design time. These policies use a TOSCA Policy Type specification as their schemas. Therefore, scripts can be used to create TOSCA policies using TOSCA Policy Types.

One straightforward way of generating concrete policies from Policy metadata in TOSCA, YAML, or other such modelling languages combined with types is to use directives specified in a script file is to use a command line utility. The command line utility is an API_User. It The script reads directives from a file. For each directive, it reads the policy model from the model file, and/or the directives from a script file and uses the information from those files to drive the concrete policy generation processtype using the Policy Type API, and uses the parameters of the directive to create a TOSCA Policy. It then uses the Policy API to create the policy.

2.2.3 Policy Design Process

All policies policy types must be certified as being fit for deployment prior to run time deployment. In the case of design-time via the SDC application, it is assumed the lifecycle being implemented by SDC will suffice for any policies policy types that are declared within the ONAP Service CSAR. For Policy Templates and raw policiesother policy types and policy type implementations, the lifecycle associated with software development process will suffice. Since models, templates and raw policies will be deployed to a Nexus repository, policy types and their implementations will be designed and implemented using software development best practices, they can be utilized and configured for various environments (eg. development, testing, production) as desired.

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In the ONAP Policy Framework, the interfaces to the PDP are designed to be as streamlined as possible. Because the PDP is the main unit of scalability in the Policy Framework, the PF is designed to allow PDPs in a PDP group to arbitrarily appear and disappear and for policy consistency across all PDPs in a PDP group to be easily maintained. Therefore, PDPs have just two interfaces; an interface that users can use to execute policies and interface to the PAP for administration, life cycle management and monitoring. The PAP is responsible for controlling the state across the PDPs in a PDP group. The PAP interacts with Nexus the Policy database and transfers policy sets to PDPs, and may cache the policy sets for PDP groups. If PDPs individually interact directly with Nexus, then a complex three-way consistency between the PDPs, PAP, and Nexus must be maintained. it is much more difficult to maintain consistency across all the PDPs in the PDP group as PDPs spontaneously appear and disappear

See also Sectino 2 of the TO BE DELETED - refer to Dublin Documentation page, where the mechanisms for PDP Deployment and Registration with PAP are explained.

2.3.1 Policy Framework Services

The ONAP Policy Framework follows the architectural approach for micro services recommended by the ONAP Architecture Subcommittee.

The ONAP Policy Framework defines Kubernetes Services to manage the life cycle of Policy Framework executable components at runtime. A Kubernetes service allows, among other parameters,  the number of instances (pods in Kubernetes terminology) that should be deployed for a particular service to be specified and a common endpoint for that service to be defined. Once the service is started in Kubernetes, Kubernetes ensures that the specified number of instances is always kept running. As requests are received on the common endpoint, they are distributed across the service instances. More complex call distribution and instance deployment strategies may be used; please see the Kubernetes Services documentation for those details.

If, for example, a service called policy-pdpd-control-loop is defined that runs 5 PDP-D instances. The service has the end point https://policy-pdpd-control-loop.onap/<service-specific-path>. When the service is started, Kubernetes spins up 5 PDP-Ds. Calls to the end point https://policy-pdpd-control-loop.onap/<service-specific-path> are distributed across the 5 PDP-D instances. Note that the .onap part of the service endpoint is the namespace being used ans and is specified for the full ONAP Kuberentes installation.

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The following diagram captures the relationship between Policy Framework concepts at run time.Image Removed

There is a one to one relationship between a policy service a PDP SubGroup, a Kubernetes PDP service, and the policies for a certain domainset of policies assigned to run in the PDP subgroup. Each PDP service is used for a particular policy domain, runs a single PDP group subgroup with multiple PDPs, which executes a specific Policy Set containing a number of policies that have been assigned to that PDP subgroup. Having and maintaining this principle makes policy deployment and administration much more straightforward than it would be if complex relationships between PDP services, groupsPDP subgroups, and policy sets.

The topology of the PDPs and their policy sets is held in the Policy Framework database and is administered by the PAP service.Image Removed

The diagram above outlines the gives an indicative structure of the run time topology information in the Policy Framework database. Note that the PDP_GROUPSUBGROUP_STATE and PDP_STATE fields hold state information for life cycle management of PDP groups and PDPs. The POLICY_MAVEN_ARTIFACT field holds a reference that a PAP can use to fetch the policy artifact from Maven.

2.3.3 Startup, Shutdown and Restart

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The PAP is the run time point of coordination for the ONAP Policy Framework. When it is started, it initializes itself using data from the database.  It then waits for periodic PDP status updates and for administration requests.

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The sequence diagram below shows the actions of the PDP at startup. See also Section 4 of the TO BE DELETED - refer to Dublin Documentation page for the API used to implement this sequence.

At startup, the PDP initializes itself.  At this point it is in PASSIVE mode. The PDP begins sending periodic Status messages to the PAP.

The first Status message initializes the process of loading the correct Policy Set on the PDP in the PAP (see Section 2.2.5.1).

On receipt or a shutdown request, the PDP completes or aborts any ongoing policy executions and shuts down gracefully.

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Policy execution can be synchronous or asynchronous. In synchronous policy execution, the component requesting a policy decision requests a policy decision and waits for the result. The PDP-X uses and PDP-A use synchronous policy execution. In asynchronous policy execution, the component that requests a policy decision does not wait for the decision. Indeed, the decision may be passed to another component. The PDP-D uses and PDP-A use asynchronous policy execution.

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Policy lifecycle management manages the deployment and life cycle of policies in PDP groups at run time. Policy sets can be deploy at run time without restarting PDPs or stopping policy execution. PDPs preserve state for minor/patch version upgrades and rollbacks.

2.3.5.1

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Load/Update Policies on PDP

The sequence diagram below shows how a Policy Set is loaded into policies are loaded or updated on a PDP.

This sequence can be initiated in three two ways; from the PDP , from Nexus, or from a user action.

1. A PDP sends regular status update messages to the PAP. If this message indicates that the PDP has no Policy Set policies or an outdated Policy Set policies loaded, then this sequence is initiated
2. Nexus triggers the PAP when a new policy set becomes available. The PAP initiates this sequence to upgrade the policy set on all PDPs running that policy set.
3. A user may explicitly trigger this sequence to load a policy set A user may explicitly trigger this sequence to load policies on a PDP

The PAP controls the entire process. The PAP reads the current  current PDP metadata from the database and reads the required policy and policy set artifacts from Nexusthe database. It then uses a PDP Plugin builds the policy set for the specific type of PDP to unpack the artifacts and build the policy set for the PDP in whatever form this type of PDP requires. The PAP supports a Java API that allows plugins to be developed for unpacking and building policies for arbitrary PDPs.Once the Policy Set has been unpacked and built, the PAP sets the mode of the PDP to PASSIVE. The Policy Set is transparently passed to the PDP by the PAP. The PDP PDP. Once the policies are ready, the PAP sets the mode of the PDP to PASSIVE. The Policy Set is transparently passed to the PDP by the PAP. The PDP loads all the policies in the policy set including any models, rules, tasks, or flows in the policy set in the policy implementations.

Once the Policy Set is loaded, the PAP orders the PDP to enter the life cycle mode that has been specified for it (ACTIVE/SAFE/TEST). The PDP beings to execute policies in the specified mode (see section 2.23.4).

2.3.5.2 Policy Rollout

A policy set steps through a number of life cycle modes when it is rolled out.

The user rolls out a policy setdefines the set of policies for a PDP group. It is deployed to a PDP group and is initially in PASSIVE mode. The user sets the PDP Group into TEST mode. The policies are run in a test or sandboxed environment for a period of time. The test results are passed back to the user. The user may revert the policy set to PASSIVE mode a number of times and upgrade the policy set during test operation.

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2.3.7 PEP Registration and Enforcement Guidelines

In ONAP there are several applications outside the Policy Framework that enforce policy decisions based on models provided to the Policy Framework. These applications are considered Policy Enforcement Engines (PEP) and roles will be provided to those applications using AAF/CADI to ensure only those applications can make calls to the Policy Decision API's. Some example PEP's are: DCAE, OOF, and SDNC.

See Section 3.

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• Should Policy Management Protocol/Policy Deployment Protocol/Policy Monitoring Protocol/Policy Persistence Protocol use DMaaP?

3.1 Policy Design APIs

Policy framework provides various APIs for users to create, update, delete (CRUD) various types of policies which include configuration (CONFIG) policies, XACML policies, Drools policies, APEX policies, etc. as well as CRUD of event schemas which are closed tied to policies in an event-driven fashion. CONFIG policies are the ones that contain detailed configurations of policy-enabled components in particular domains, which are basically in the format of key-value pairs. They will be subscribed by DCAE Micro-Services or other policy-enabled components. It is an important area the framework should provide backwards compatibility support when APIs are redesigned and evolving. XACML policies are typically access/admission control policies thus can be seamlessly specified for policy guard. Drools/APEX policies are action policies which will make runtime decisions reacting to particular network events via concrete actions or action guidance. They play a critical role in control loop implementation and management. Event schemas are as important as policies since all the policies are event-driven. Context/situation information are embedded in the input events. By knowing the semantics of events, policy rules can capture the logic of parsing the events, decide what reaction to come up with and how. Changing event schema will somehow impact policy logic. Hence, CRUD of event schemas are taken into account along with policy design.

Policy framework provides multiple options of creating policies to various types of users. Some users might be domain experts with proficient programming skills. They would probably like to compose the policies from scratch (a.k.a. raw policies) and are able to write templates for parametrized policies in particular domains. Providing policy CRUD option for such users is inevitable. There is another type of users who are not capable of writing raw policies and templates but have good understanding of existing templates and know what template they should use and what data to populate into the template in order to support real-world use cases. Hence, exposing APIs for CRUDing template-based policies to such users should also be considered. In addition, designing APIs for CRUDing event schemas is needed as well given event schema design can also be taken as a part of policy design. When user designs a policy, they also design the input and output events to/from the policy. Hence, event schemas will be included in policy payload. To ease re-usability of event schema, in each policy payload, user just needs to specify the names of new/existing schemas they want to use in current policy. Eligibility of specified schemas will be validated by the framework before the policy is being processed. 

3.1.1 Data Model for APIs

The very first step of API design is to come up with data models for various API objects. Hence, data models for policy, policy template and event schema are in our scope here.

Data models for the APIs can be downloaded from here:  API-MODEL-Policy.json, API-MODEL-Policy_Template.json, API-MODEL-Event_Schema.json

It is worth noting that above listed models are generic ones to support CRUD of various types of policies by various types of users (i.e. DEV users who know how to program policies/templates and know how to package/generate maven artifact and do maven deployment; GUI users who will CRUD template-based policies via GUI only), and have backwards compatibility with existing CONFIG policies and XACML guard policies.

3.1.2 Raw Policy Creation

An important API is to support CRUD of raw policy. The "raw" here means the policy is composed from scratch, not based on any template. We assume such API users are all DEV users who master policy programming using native policy language provided by each policy engine and know how to do maven compilation, artifact generation and deployment given policy will be stored as maven artifact. The sequence diagram is shown below.

The first step is for DEV user to wrap up policy artifact with details included in the note below, submit it to governance process for validation, then deploy it to nexus repository. Next, POST /policy/raw is invoked to create raw policy with payload populated (payload format is in the note below). It is worth noting that since policy contents/rules are already included in the artifact which has been deployed to nexus, there is no need to put them again in the payload "data" field. Hence, only "metadata" is meaningful for the payload here.

After the API is invoked, the first thing is to check the eligibility of event schemas specified in the payload, checking whether each event schema name has one matching entry in DB SCHEMA table. If yes, save policy metadata to Database to keep a record.

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3.1.3 Policy Template Creation

DEV users are capable of not only programming raw policies, but programming policy templates which expose several parameters to be populated by GUI users. In other words, we assume templates are being created by only DEV users. The sequence diagram is shown below. Given DEV users know programming and maven deployment, similarly, we require them to deploy template archetype artifact to nexus by themselves as the first step. It is worth noting that template contents would be different for various types of policy. It is also noted below. For example, Drools policy template would be Drools rules with configurable parameters in .drl file; XACML policy template would be xacml policies/rules with configurable parameters in .xml file; APEX policy template would be APEX policy model with configurable parameters in .apex file; CONFIG policy template can be defined as a JSON file with configurable parameters.

Different from policy artifact, in addition to template metadata and contents, template archetype artifact also contains the descriptor of configurable parameters to populate the template, which is stored in archetype.xml, noted below. Also, a new field called "populateDataSchema" is specified in payload which is used to indicate the schema type such as JSON, YAML, TOSCA and so on. TOSCA is referred to existing TOSCA policy schema for backwards compatibility with CONFIG policy.

The rest of the flows are similar. After POST /template API is invoked, event schema eligibility will be checked first. Then template metadata will be saved to Database as a record.

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3.1.4 Template-Based Policy Creation by DEV user

Given template archetype artifact is created and deployed to nexus, for the users who want to base the template to create concrete policies, the first step is to review existing templates and select one to work on. The key to create policy based upon a template is to populate the template by required parameter values. It can be done by maven archetype plugin - archetype:generate given template is stored as archetype artifact. Here, we design different flows for different types of users. The sequence diagram for DEV users is shown below. For DEV users who master maven and would like to do programming, they can do API calls GET /templates and GET /template/{template-id} to review existing templates and select one to work on, then use maven archetype generate plugin to populate the template by their own. After wrapping up the policy artifact, DEV users should deploy it to nexus as before, followed by invoking template-based policy creation API to save policy metadata to Database.

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3.1.5 Template-Based Policy Creation by GUI user

TBD - No Resources to work on the GUI

Another type of users who prefer to manipulate template-based policies through GUI. Thus, we call them GUI users here, without loss of generality. The sequence diagram is shown below. Basically, all such users' operations are through GUI, including reviewing/selecting existing templates and populating selected template by providing values to fill out configurable parameters in the template. The options to fill configurable parameters should be rendered by GUI. The configurable parameters here include those embedded in the template and the ones in policy metadata like "artifactId", "version" and so on. GUI backend will invoke corresponding API calls and pass in API arguments upon users' input in the GUI. It is worth noting that, in this scenario, all parameter values used to populate the template are specified in the "data" field of the payload and passed in to the API call. PAP will call maven archetype generation plugin to package a policy artifact on top of a populated template and do nexus deployment.

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3.1.6 Event Schema Creation

Since all the policies are event-driven, which means they will be triggered by input events and generate necessary output events to downstream actioning systems that will enforce the policies. Thus, designing event schemas is a part of policy design. Corresponding API is provided to CRUD event schema. Sequence diagram is shown below. Note that event schemas need to be specified during policy creation, and their eligibility will be checked. Thus, for the users who want to create a new policy, it is preferred that they know what event schemas are existing and ready to be used or they can create new event schemas to support particular policies and user cases. It is worth noting that before saving new schema to Database, it will be checked if it is a new schema that has not been created before so that it is guaranteed every event schema stored in Database is unique and will not cause ambiguity.

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3.1.7 Policy Query via API

Policy query design is still WIP. Initial thoughts are collected in the sequence diagram shown below.

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3.1.8 Policy Query via GUI

WIP. Initial results are shown below.

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3.2 Policy Deployment APIs

PAP to all PDPs in PDP group

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• Update of policies across PDPs in a PDP group use "eventually consistent" semantics, transactions or ACID semantics will not be supported
• Event though PDPs could listen or monitor Nexus for updates to policies, the PAP should be the component responsible for deciding if and what policy upgrades are propagated to the entire PDP group.

PDP Group Admin in PAP

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PAP to all PDPs in PDP group

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• *A policy may be parameterized. There are two ways to handle this
  • Combine a raw policy into a parameterized policy and deploy the parameterized policy at run time
  • Have the raw policy and its parameters as separate artifacts and deploy them separately
  • Do not consider the parameters as an artifact but allow them to be modified directly by users setting them using an interface towards the PAP at run time

Policy Execution (Users to PDP Group pr PDP)

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• **Applications using the Policy Framework should not be aware of specific PDPs, we should only support this behaviour for existing users and deprecate this usage.
• Load Balancing across PDP group......Stateless PDPs no problem.....set up stateful transfer between PDPs if supported....Address specific PDPs

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4. The Policy Framework Implementation

• Database off PAP (PDPs report back to PAP, don’t access database directly)
• Database could be replaced by/interchangeable with some ONAP persistence system (DMaaP or DCAE)?

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Observations

• Policy-core has definitions of the Policy protocols and the interfaces for all the interactions between the policy components. It doesn’t have much functional code, it’s mainly the model of the system and to enforce the overall structure and interactions in the system. Some of the current engine goes in there. Implementation of the protocols is in this modules including the Inter-PDP protocol and the generic parts of the Intra-PDP protocol
• PAP functionality extended to do life cycle monitoring and run time monitoring of PDPs, moves out of engine to separate git repository. The Deployment and Monitoring could be separate modules
• Generic PDP functionality is in a separate PDP module, the current generic PDP functionality moves there and is extended to provide generic model driven PDP support for arbitrary PDPs
• PDP-X specific functionality goes to the PDP-X module
• PDP-D and BRMSGW combined in PDP-D (PDP-D related functions in engine and the current drools-pdp combined)
• The drools-applications module generalized to provide interfaces for all the Policy Framework including arbitrary PDPs towards the other ONAP components in the Policy Interactions module. This must have a mechanism to allow model-driven interactions, in other words define interfaces at run time rather than at design time in Java or JAXB.
• All persistence is In the Policy Persistence module in order to keep persistence nastiness out of the other modules, state from PDPs can be persisted by reading state over the Policy Management Protocol. The Policy Management Protocol could use Distributed Hash Maps to share state with Persistence.
• All PDP implementations specialize the generic interfaces from Policy-core and PDP and can extend the Intra-PDP protocol with PDP-specific support, for example for state and context sharing
• Not much thought gone into the Portal as yet except that it will use REST interfaces for interactions.

4.1 Policy Design Implementation

• The Policy GUI Dashboard is created from the ONAP Portal SDK to create a consistent user experience
• The Policy GUI Designer is created from the ONAP SDC SDK to create a consistent user experience

4.2 Policy Deployment Implementation

4.3 Policy Execution Implementation

4.4 Policy Repository Layout

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Unused in Casablanca

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The XACML PDP implementation

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This repo will hold the next generation Apex PDP engine

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4 of the TO BE DELETED - refer to Dublin Documentation for more information on the Decision APIs.

3. APIs Provided by the Policy Framework

See the TO BE DELETED - refer to Dublin Documentation page.

4. Terminology

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