[OASIS Issue Tracker] Commented: (TOSCA-141) WD02 - Specifying Environment Constraints for Node Templates

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    [ http://tools.oasis-open.org/issues/browse/TOSCA-141?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=36713#action_36713 ] 

Thomas Spatzier  commented on TOSCA-141:
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I think this kind of semantics can be expressed with a grouping mechanism as we currently have in the document. My concern with the proposed change is that we are introducing a new top-level section for one specific use case, and we will probably introduce more such sections as we go on, making the overall TOSCA document structure overly complex.

The goal of the grouping mechanism was to have a simple to use way of expressing certain constraints on two or more nodes, which could be used for many use cases. One use case was anti-collocation. The current draft certainly needs some more work, but I would opt for trying to stick with one section and syntax that can be applied to many use cases instead of common up with potentially different top-level sections for specific use cases.

> WD02 - Specifying Environment Constraints for Node Templates
> ------------------------------------------------------------
>
>                 Key: TOSCA-141
>                 URL: http://tools.oasis-open.org/issues/browse/TOSCA-141
>             Project: OASIS Topology and Orchestration Specification for Cloud Applications (TOSCA) TC
>          Issue Type: Bug
>          Components: Profile-YAML
>            Reporter: Derek Palma
>            Assignee: Derek Palma
>
> In section 12 Grouping Node Templates, a membership construct is used to associate a TOSCA runtime constraint (a capability not provided by the nodes in the service template but by the environment that is processing it) to a set of node templates, the subjects of the constraint.
> The specific use cases is an anti-colocation constraint to ensure two SoftwareComponents are not placed on the same Compute node which is certainly a valid and common use case.
> My concern with the proposed syntax is that is that it is not able to support strong validation. This construct should capture the following semantics:
> 1)	The capability of the TOSCA Runtime to be applied (constrained)
> 2)	The subjects of the action implied by the declarative constraint

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