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

    [ http://tools.oasis-open.org/issues/browse/TOSCA-3?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=29665#action_29665 ] 

Frank Leymann  commented on TOSCA-3:

A Policy Attachment is a separate entity.  The same is true for a Policy itself.  Thus, a Policy Attachment establishes a link between a separately defined Policy, and an element in a Service Template file.  This allows for easy reuse of Policies (e.g. policies defining payment methods, availability characteristics etc).  Such a Policy may be reused by simply referencing it in a Policy Attachment, and the Policy Attachment references an element (e.g. a Node Template) or a set of elements that are then associated with the referenced Policy.  This also allows to easily change policies assigned to elements in a Service Template without having to change the Service Template files accordingly, having to re-import them again in a TOSCA envronment etc. 

> 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
>            Reporter: Frank Leymann 
>            Assignee: 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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