Abstract

This document describes the ONAP Policy Framework. It lays out the architecture of the framework and specifies the APIs provided to other components that interwork with the framework. It describes the implementation of the framework, mapping out the components, software strucure, and execution ecosystem of the framework. It goes on to provide examples that illustrate how to write, deploy, and run policies of various types using the framework.

1. Overview

The ONAP Policy Framework is a comprehensive policy design, deployment, and execution environment. The Policy Framework is the decision making component in an ONAP system. It allows you to specify, deploy, and execute the governance of the features and functions in your ONAP system, be they closed loop, orchestration, or more traditional open loop use case implementations. The Policy Framework is the component that is the source of truth for all policy decisions.

One of the most important goals of the Policy Framework is to support Policy Driven Operational Management during the execution of ONAP control loops at run time. In addition, use case implementations such as orchestration and control benefit from the ONAP policy Framework because they can use the capabilities of the framework to manage and execute their policies rather than embedding the decision making in their applications.

The Policy Framework is deployment agnostic, the Policy Framework manages Policy Execution (in PDPs) and Enforcement (in PEPs) regardless of how the PDPs and PEPs are deployed. This allows policy execution and enforcement can be deployed in a manner that meets the performance requirements of a given application or use case. In one deployment, policy execution could be deployed in a separate executing entity in a Docker container. In another, policy execution could be co-deployed with an application to increase performance.

The ONAP Policy Framework architecture separates policies from the platform that is supporting them. The framework supports development, deployment, and execution of any type of policy in ONAP. The Policy Framework is metadata (model) driven so that policy development, deployment, and execution is as flexible as possible and can support modern rapid development ways of working such as DevOps. A metadata driven approach also allows the amount of programmed support required for policies to be reduced or ideally eliminated.

We have identified five capabilities as being essential for the framework:

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 model driven policy design approach for policy type programming and specification of policies.

5. It must be extensible, allowing straightforward integration of new PDPs, policy formats, and policy development environments.

Another important aim of the architecture of a model driven policy framework is that it enables much more flexible policy specification. The ONAP Policy Framework complies with the TOSCA modelling approach for policies, see the TOSCA Policy Primer for more information on how policies are modelled in TOSCA.

1. A Policy Type is a general implementation of a policy for a feature. For example, a Policy Type could be written to manage Service Level Agreements for VPNs. The Policy Type is designed by a domain expert, who specifies the parameters, triggers, and actions that the Policy Type will have. The implementation (the logic, rules, and tasks of the Policy Type) is implemented by a skilled policy developer in consultation with domain experts.

   1. For example, the VPN Policy Type is used to create VPN policies for a bank network, a car dealership network, or a university with many campuses.

   2. In ONAP, specific ONAP Policy Types are used to create specific policies that drive the ONAP Platform and Components.

2. A Policy is created by configuring a Policy Type with parameters. For example, the SLA values in the car dealership VPN policy for a particular dealership are configured with values appropriate for the expected level of activity in that dealership.

The ONAP Policy Framework for building, configuring and deploying PDPs is extendable. It allows the use of ONAP PDPs as is, the extension of ONAP PDPs, and lastly provides the capability for users to create and deploy their own PDPs. The ONAP Policy Framework provides distributed policy management for all policies in ONAP at run time. Not only does this provide unified policy access and version control, it provides life cycle control for policies and allows detection of conflicts across all policies running in an ONAP installation.

2. Architecture

The diagram below shows the architecture of the ONAP Policy Framework at its highest level.

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. PolicyDevelopment interacts with ONAP design time components, and has no programmatic interface with PolicyAdministration, PolicyExecution or any other run-time ONAP components.

The diagram below shows a more detailed view of the architecture, as inspired by RFC-2753 and RFC-3198.

PolicyDevelopment provides a CRUD API for policy types and policies. The policy types and policy artifacts and their metadata (Information about policies, policy types, 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 types and policies.

PolicyAdministration has two important functions:

• Management of the life cycle of PDPs in an ONAP installation. PDPs register with PolicyAdministration when they come up. PolicyAdministration handles the allocation of PDPs to a PDP Groups and PDP Subgroups, so that they can be managed as microservices in Kubernetes.

• Management of the deployment of policies to PDPs in an ONAP installation. PolicyAdministration gives each PDP group a set of domain policies to execute.

PolicyAdministration handles PDPs and policy allocation to PDPs using asynchronous messaging over DMaaP.

PolicyAdministation provides three APIs:

• a CRUD API for policy groups and subgroups

• an API that allows the allocation of policies PDP groups and subgroups to be controlled

• an API allows policy execution to be managed, showing the status of policy execution on PDP Groups, subgroups, and individual PDPs as well as the life cycle state of PDPs

PolicyExecution is the set of running PDPs that are executing policies, logically partitioned into PDP groups and subgroups.

The figure above shows how PolicyExecution looks at run time with PDPs running in Kubernetes. A PDPGroup is a purely logical construct that collects all the PDPs that are running policies for a particular domain together. A PDPSubGroup is a group of PDPs of the same type that are running the same policies. A PDPSubGroup is deployed as a Kubernetes Deployment. PDPs are defined as Kubernetes Pods. At run time,  the actual number of PDPs in each PDPSubGroup is specified in the configuration of the Deployment of that PDPSubGroup in Kubernetes. This structuring of PDPs is required because, in order to simplify deployment and scaling of PDPs in Kubernetes, we gather all the PDPs of the same type that are running the same policies together for deployment.

For example, assume we have policies for the SON (Self Organizing Network) and ACPE (Advanced Customer Premises Service) domains. For SON, we have XACML, Drools, and APEX policies, and for ACPE we have XACML and Drools policies. The table below shows the resultingPDPGroup, PDPSubGroup, and PDP allocations:

2.1 Policy Framework Object Model

This section describes the structure of and relations between the main concepts in the Policy Framework. This model is implemented as a common model and is used by PolicyDevelopment, PolicyDeployment, and PolicyExecution.

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.

2.2 Policy Design Architecture

This section describes the architecture of the model driven system used to develop policy types and to create concrete policies using policy types. The output of Policy Design is deployment-ready artifacts and Policy metadata in the Policy Framework database.

Policies that are expressed via natural language or a model require some development work ahead of time for them to be translated into concrete runtime policies. Some Policy Domains will be setup and available in the platform during startup such as Control Loop Operational Policy Models, OOF placement Models, DCAE microservice models. Policy type implementation development is done by an experienced developer.

2.2.1 Policy Type Design

Policy Type Design is the task of creating policy types that capture the generic and vendor independent aspects of a policy for a particular domain use case. The policy type implementation specifies the model information, rules, and tasks that a policy type requires to generate concrete policies.

All policy types must implement the ONAP Policy Framework PolicyType interface. This interface allows PolicyDevelopment to manage policy types and to generate policies from these policy types in a uniform way regardless of the domain that the policy type is addressing or the PDP technology that will execute the policy. The interface is used by PolicyDevelopment to determine the PDP technology of the policy type, the structure, type, and definition of the model information that must be supplied to the policy type to generate a concrete policy.

A PolicyTypeImpl is developed for a certain type of PDP (for example XACML oriented for decision policies or Drools rules oriented for ECA policies). The design environment and tool chain for a policy type is specific for the type of policy being designed.

The PolicyTypeImpl  implementation (or raw policy) is the specification of the specific rules or tasks, the flow of the policy, its internal states and data structures and other relevant information. A PolicyTypeImpl is specific to a PDP technology, that is XACML, Drools, or APEX. A PolicyTypeImpl can be specific to a particular policy type, it can be more general, providing the implementation of a class of policy types, or the same policy type may have many implementations.

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 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.