POLICY is a subsystem of ONAP that maintains, distributes, and operates on the set of rules that underlie ONAP’s control, orchestration, and management functions. 

POLICY provides a logically centralized environment for the creation and management of policies, including conditional rules.  This provides the capability to create and validate policies/rules, identify overlaps, resolve conflicts, and derive additional policies as needed.  Policies are used to control, influence, and help ensure compliance with goals.  Policies can support infrastructure, products and services, operation automation, and security.  Users, including network and service designers, operations engineers, and security experts, can easily create, change, and manage policy rules from the POLICY Manager in the ONAP Portal.

The figure below represents the target POLICY Architecture.

The figure below represents the current POLICY Architecture.

A policy is defined to create a condition, requirement, constraint, decision, or a need that must be provided, evaluated, maintained, and/or enforced.  The policy is validated and corrected for any conflicts, and then placed in the appropriate repository, and made available for use by other subsystems and components.  Alternately, some policies are directly distributed to policy decision engines such as Drools or XACML.   In this manner, the constraints, decisions and actions to be taken are distributed.

System Architecture

ONAP POLICY is composed of several subcomponents: the Policy Administration Point (PAP), which offers interfaces for policy creation, and two types of Policy Decision Point (PDP), each based on a specific rules technology.  PDP-X is based on XACML technology and PDP-D is based on Drools technology.  PDP-X is stateless and can be deployed as a resource pool of PDP-X servers.  The number of servers can be grown to increase both capacity (horizontal scalability) and to increase availability.  The PDP-D is stateful, as it utilizes Drools in its native, stateful way and transactions persist so long as the PDP-D is active.  Persistent Drools sessions, state management, local and geo-redundancy have been deactivated for the initial release of ONAP POLICY and can be turned on in a future release.  Additional instances of XACML/Drools engines and assigned roles/purposes may also be added in the future to provide a flexible, expandable policy capability.

As illustrated in the Figure below, the POLICY components are supported by a number of interfaces and subsystems.  The ONAP Portal provides a human interface for the creation, management and deployment of policies.  It is a web-based system that utilizes POLICY APIs provided by the PAP.

The PAP provides interfaces for the management of policies.  It utilizes the XACML database to store policies, which are then distributed to the PDPs.

The XACML and Drools databases are hosted in a MariaDB cluster.  The XACML database is used to persist policies and policy dictionaries and provide a point for PDPs to retrieve policies.  The XACML database also has tables used for node state management, detection of node failure and failover. As indicated above, the state management tables will only include entries for the PAP and PDP-X as the testing is not yet complete for the PDP-D.

The PDP-X receives deployed policies and has interfaces to handle XACML policy transactions.  These transactions are stateless and once complete, they are removed from memory.  If a policy that is deployed to the PDP-X is of an operational nature it will contain Drools rules and Java executables.  These artifacts are processed into Maven artifacts and pushed to the Maven repository.  The PDP-D is then notified a new policy has been deployed.

When the PDP-D is notified a new policy has been deployed, it downloads it from the Maven repository and assigns it to an internal controller.  This controller provides the external Closed Loop interfaces to the DMaaP message bus over which events and messages are exchanged with external systems.  As events or messages arrive at the PDP-D, they are assigned to the appropriate controller and a Drools session is either created or retrieved from memory.  The events, messages or facts are passed to the Drools session and the corresponding rule is fired, resulting in a change of internal session state and possibly actions taken in response to the rule processing. Response messages and requests are passed by the controller back over the DMaaP message bus to the appropriate system.  The Drools session can also have timers and autonomous events. In a future release the PDP-D can enable the node state management and session persistence in the Drools DB.

Policy Creation

The Policy Creation component of the Policy subsystem enables creation of new policies and modification of existing polices, both during the design phase and during runtime.  Policy Creation is targeted to be integrated to a unified Service Design and Creation (SDC) environment.

A policy can be defined at a high level to create a condition, requirement, constraint, decision or a need that must be provided, evaluated, maintained, and/or enforced. A policy can also be defined at a lower or functional level, such as a machine-readable rule or software condition/assertion which enables actions to be taken based on a trigger or request, specific to particular selected conditions in effect at that time. 

Some examples of types of policies are:

• VNF placement — rules governing where VNFs should be placed, including affinity rules
• Data and feed management — what data to collect and when, retention periods, and when to send alarms about issues
• Access control — who (or what) can have access to which data
• Trigger conditions and actions — what conditions are actionable, and what to do under those conditions
• Interactions — how interactions between change management and fault/performance management are handled (for example, should closed loops be disabled during maintenance?)

Policy Decision and Enforcement

Run-time policy enforcement is performed by ONAP subsystems that are policy-enabled or can respond to commands from a policy-enabled element such as a PDP.  For example, policy rules for data collection are enforced by the data collection functionality of DCAE. Analytic policy rules, identification of anomalous or abnormal conditions, and publication of events signaling detection of such conditions are enforced by DCAE analytic applications.  Policy rules for associated remedial actions, or for further diagnostics, are enforced by the correct component in a control loop such as the MSO, a Controller, or DCAE.  Policy engines such as XACML and Drools also enforce policies and can trigger other components as a result (for example, causing a controller to take specific actions specified by the policy).  Additionally, some policies (“Guard Policies”) may enforce checks against decided actions.