This page gives a short overview of how Policy is modelled in the TOSCA Simple Profile in YAML.
TOSCA defines three concepts for Policy: Policy Type, Policy, and Trigger.
1. Policy Type
A Policy Type is used to specify the types of policies that may be used in a service. The parameters of a policy of this type, the entity types to which it applies, and what triggers policies of this type are specified.
The types of policies that are used in a service are defined in the policy_types section of the TOSCA service template as a Policy Type. More formally, TOSCA defines a Policy Type as an artifact that "defines a type of requirement that affects or governs an application or service’s topology at some stage of its lifecycle, but is not explicitly part of the topology itself". In the definition of a Policy Type in TOSCA, you specify:
- its properties, which define the configuration parameters that the policy takes
- its targets, which define the node types and/or groups to which the policy type applies
- its triggers, which specify the conditions in which policies of this type are fired
2. Policy
A Policy is used to specify the actual instances of policies that are used in a service. The parameters of a policy, the entity types to which it applies, and what triggers the policy are specified.
The types of policies that are used in a service are defined in the policy_types section of the TOSCA service template as a Policy Type. More formally, TOSCA defines a Policy Type as an artifact that "defines a type of requirement that affects or governs an application or service’s topology at some stage of its lifecycle, but is not explicitly part of the topology itself". In the definition of a Policy Type in TOSCA, you specify:
- its properties, which define the configuration parameters that the policy takes
- its targets, which define the node types and/or groups to which the policy type applies
- its triggers, which specify the conditions in which policies of this type are fired