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Subject: [OASIS Issue Tracker] Created: (TOSCA-3) Grouping Element for Policies

Grouping Element for Policies

                 Key: TOSCA-3
                 URL: http://tools.oasis-open.org/issues/browse/TOSCA-3
             Project: OASIS Topology and Orchestration Specification for Cloud Applications (TOSCA) TC
          Issue Type: Improvement
          Components: Spec
    Affects Versions: WD1
            Reporter: Frank Leymann 

A grouping element is missing that allows to assign policies to collections of node templates. For example, a policy specifies that the energy consumption of instances of a subset of node templates must not exceed a certain threshold; this is difficult to achieve by specifying a (lower) threshold of energy consumption to each member of the subset. Another policy specifies that instances of another subset of node templates must be of a certain availability class. These subsets might have a non-empty intersection. 

We have a group element already (i.e. <GroupTemplate>) the purpose of which is to define "subtrees" of topology templates for reuse. This purpose is different from the proposed grouping element for policy assignments. 

For example, Group Templates are instantiated (specifying their minimum and maximum number of instances) while the proposed grouping element for policy assignment is not separately instantiatable. The current spec does not explicitly exclude intersecting Group Templates, but it seems to be unclear what that means: E.g. a node template in two Group Templates is target of one relationship type the specifies cascading deletion, and target of another relationship type with no cascading deletion - what is the resulting behavior? Similarly, a node template is in two Group Templates each of which specifies a maximum number of instances - do the number of instances of the node templates in the intersection sum up?  N.B.: Maybe a clarification of this is worth a separate issue....

Thus, a new language element for collective policy assignment seems to be justified. 

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