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This section describes the architecture of the model driven system used to develop policy templates, to derive concrete policies from those policy templates, and to parameterize concrete policies as executable policies. The output of Policy Design is deployment-ready artifacts in Maven and Policy metadata in the Policy Framework database.
2.1.1 Policy Template Design
Policy Template Design is the task of creating policy templates that capture the generic and vendor independent aspects of a policy for a particular domain use case. The policy template also specifies and publishes the model information, rules, and logic tasks that it requires to generate concrete policies.
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All policy templates must implement the ONAP Policy Framework PolicyTemplate interface. This interface allows the Policy Framework to manage policy templates and to generate concrete policies from policy templates in a uniform way regardless of the domain that the policy template is addressing or the PDP technology that will execute the policy. The interface is used by the Policy Framework to determine the PDP technology of the policy template, the structure, type, and definition of the model information that must be supplied to the policy template to generate a concrete policy, implementation specific rules or logictasks, the flow of the policy, and other relevant information.
The ONAP Policy Framework provides an API that the RESTful Policy Design API, which allows other components to query policy templates, to determine the model information, rules, or logic tasks that they require, to specialize policy flow, and to generate concrete policies from policy templates. This API is used by the ONAP Policy Framework and other components such as SDC to create concrete policies from policy templates.
Consider a policy template created for managing Consider a policy template created for managing faults on vCPE equipment in a vendor independent way. The policy template captures the generic logic required to manage the faults and specifies the vendor specific information that must be supplied to te template for specific vendor vCPE VFs. The actual concrete vCPE policy that is used for managing particular vCPE equipment is generated using the policy template together with the specific modeled information, rules and logic tasks for that vendor model of vCPE.
2.1.1.1 Programming Policy Templates
The most straightforward way to create a policy template is to program it. Programming a policy template might simply mean creating and editing text files and manually generating the Maven artifact for the policy template.
A more formal approach is preferred. Programmers use a specific Eclipse project type for developing each type of policy template, a Policy Template SDK. The project is under source control in git. This Eclipse project is structured correctly for creating policies for a specific type of PDP. It includes the correct POM files for generating the policy template as a Maven artifact. It has editors and perspectives that aid the programmer in their work.
2.1.1.2 Generating Policy Templates
It is also possible to generate policy templates using MDD (Model Driven Development) techniques. Policies are expressed using a DSL (Domain Specific Language) or a policy specification environment for a particular application domain. For example, policies for specifying SLAs could be expressed in a SLA DSL and policies 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 templates.
2.1.2 Policy Design
Policy Design is the task of creating creates a concrete policy from a policy template.
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The information expressed during policy design is used to specialize a policy template to create an executable policy.
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A number of mechanisms for policy design that are supported in ONAP. The process in the ONAP Policy Framework for generating a concrete policy is the same for all mechanisms. The most general mechanism for creating a concrete policy is using the RESTful Policy Design API, which provides a full interface to the templating and concrete policy generation support of the Policy Framework. This API may be exercised directly using utilities such as curl. The Policy Framework provides a command line tool that is a loose wrapper around the API. It also provides a general purpose client in the ONAP Portal for policy generation, which again is a general purpose wrapper around the Policy Design API.
A number of ONAP components use policy in manners which are specific to their particular needs. The manner in which the policy creation process is triggered and the way in which information required to specialize a policy template is specified and accessed is specialized for these ONAP components.
2.1.2.1 Model Driven VF (Virtual Function) Policy Design via VNF SDK Packaging
VF vendors express policies such as SLA, Licenses, hardware placement, run-time metric suggestions, etc. These details are captured within the VNF SDK and uploaded into the SDC Catalog. The SDC Distribution APIs are used to interact with SDC. For example, SLA and placement policies may be captured via TOSCA specification. License policies can be captured via TOSCA or XACML specification (TBD). Run-time metric vendor recommendations can be captured via VES Standard specification. The sequence diagram below is a high level view of SDC-triggered concrete policy generation for some arbitrary entity EntityA.
2.1.2.2 Model Driven Policy Design via SDC GUI
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). Service policies such as Optimization, Placement policies can also be captured via TOSCA model during design time.
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