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@@ -21,6 +21,64 @@ PDP group to arbitrarily appear and disappear and for policy consistency across
maintained. The PAP is responsible for controlling the state across the PDPs in a PDP group. The PAP interacts with the
policy database and transfers policies to PDPs.
+The unit of execution and scaling in the Policy Framework is a *PolicyImpl* entity. A *PolicyImpl* entity runs on a PDP.
+As is explained above, a *PolicyImpl* entity is a *PolicyTypeImpl* implementation parameterized with a TOSCA *Policy*.
+
+.. image:: images/PolicyImplPDPSubGroup.svg
+
+In order to achieve horizontal scalability, we group the PDPs running instances of a given *PolicyImpl* entity logically
+together into a *PDPSubGroup*. The number of PDPs in a *PDPSubGroup* can then be scaled up and down using Kubernetes. In
+other words, all PDPs in a subgroup run the same *PolicyImpl*, that is the same policy template implementation (in
+XACML, Drools, or APEX) with the same parameters.
+
+The figure above shows the layout of *PDPGroup* and *PDPSubGroup* entities. The figure shows examples of PDP groups for
+Control Loop and Monitoring policies on the right.
+
+The health of PDPs is monitored by the PAP in order to alert operations teams managing policies. The PAP manages the life
+cycle of policies running on PDPs.
+
+The table below shows the deployment methods in which *PolicyImpl* entities can be deployed to PDP Subgroups.
+
+========== =========================================== ============================== ==================================
+**Method** **Description** **Advantages** **Disadvantages**
+========== =========================================== ============================== ==================================
+Cold The *PolicyImpl* (*PolicyTypeImpl* and No run time configuration Very restrictive, no run time
+ TOSCA *Policy*) are predeployed on the PDP. required and run time configuration of PDPs is possible.
+ PDP is fully configured and ready to administration is simple.
+ execute when started.
+
+ PDPs register with the PAP when they
+ start, providing the *pdpGroup* they
+ have been preconfigured with.
+
+Warm The *PolicyTypeImpl* entity is predeployed The configuration, parameters, Administration and management is
+ on the PDP. A TOSCA *Policy* may be loaded and PDP group of PDPs may be required. The configuration and
+ at startup. The PDP may be configured or changed at run time by loading life cycle of the TOSCA policies
+ reconfigured with a new or updated TOSCA or updating a TOSCA *Policy* can change at run time and must be
+ *Policy* at run time. into the PDP. administered and managed.
+
+ PDPs register with the PAP when they start, Support TOSCA *Policy* entity
+ providing the *pdpGroup* they have been life cycle managgement is
+ predeployed with if any. The PAP may update supported, allowing features
+ the TOSCA *Policy* on a PDP at any time such as *PolicyImpl* Safe Mode
+ after registration. and *PolicyImpl* retirement.
+
+Hot The *PolicyImpl* (*PolicyTypeImpl* and The policy logic, rules, Administration and management is
+ TOSCA *Policy*) are deployed at run time. configuration, parameters, and more complex. The *PolicyImpl*
+ The *PolicyImpl* (*PolicyTypeImpl* and PDP group of PDPs may be itself and its configuration and
+ TOSCA *Policy*) may be loaded at startup. changed at run time by loading life cycle as well as the life
+ The PDP may be configured or reconfigured or updating a TOSCA *Policy* cycle of the TOSCA policies can
+ with a new or updated *PolicyTypeImpl* and *PolicyTypeImpl* into the change at run time and must be
+ and/or TOSCA *Policy* at run time. PDP. administered and managed.
+
+ PDPs register with the PAP when they Lifecycle management of TOSCA
+ start, providing the *pdpGroup* they have *Policy* entities and
+ been preconfigured with if any. The PAP may *PolicyTypeImpl* entites is
+ update the TOSCA *Policy* and supported, allowing features
+ *PolicyTypeImpl* on a PDP at any time after such as *PolicyImpl* Safe Mode
+ registration and *PolicyImpl* retirement.
+========== =========================================== ============================== ==================================
+
1 APIs
======