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Subject: [OASIS Issue Tracker] Commented: (TOSCA-115) Requirements Capabilities to provide interfaces
[ http://tools.oasis-open.org/issues/browse/TOSCA-115?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=36122#action_36122 ]
Derek Palma commented on TOSCA-115:
-----------------------------------
It's important to clearly delineate between the purposes of Node Types and Capability Types in the context of the current intent of the specification.
Node Types represent kinds of deployable entities with lifecycles and stateful interdependencies among other Node Types (deployable entities). These interdependencies are expressed with Relationship Types.
Capability Types represent the ability of a Node Type to support a specific behavior, feature, or mode of operation. Capability Types are standalone types and thus can be used by multiple Node Types.
This proposal tries to implement composition, e.g. a Node Type can be a web server or a database or both by specifying the web server and database semantics through Capability Types. This is incorrect assuming the objective is to deploy software components which realize web server and database functionality because:
1) The web server and database both have lifecycles states they must transition through
2) Both require different deployment artifacts for the materialization of the respective Node Instances
3) Correct operation of these components requires their orchestration consider their interdependencies
4) You may want to control the scalability, e.g. horizontally scale the Web Servers
These are very fundamental requirements. The intent of TOSCA is that the web server and database are most appropriately modeled as Node Types. I.e. Capability Types should not be used to compose entities at the "meta" level. The correct approach is explicitly supported with the hostedOn Relationship Type, where a container such as a compute node or operating system can "host" web servers and databases. In modeling, this is typically referred as hierarchical composition. Moreover, since the web servers and databases could be collocated in the same containers or placed in separate containers because the complete deployment semantics around interdependencies are sufficiently captured and generalized.
> Requirements Capabilities to provide interfaces
> -----------------------------------------------
>
> Key: TOSCA-115
> URL: http://tools.oasis-open.org/issues/browse/TOSCA-115
> Project: OASIS Topology and Orchestration Specification for Cloud Applications (TOSCA) TC
> Issue Type: New Feature
> Affects Versions: V1.1_CSD01
> Reporter: Kevin Wilson
>
> Requirements and capabilities should provide specific interface definitions. So that the designer of a app can depend on a contract set of public properties that are to be provided and a contracted set method/interfaces that are provided by the requirement.
> For example:
> If I have a dependency on a DB Server, and need to run SQL on that server, at design time, I would like to know the methods supported by the DBServer requirement so that I can leverage that in my component scripting.
> On the implementation side providing the component, the script/method to execute the script may be different for each DBServer type. IE commands to run SQL on MySQL are not the same commands that would be used for Oracle. However, the SQL may the same in some cases.
> Similar methods/use cases exist for J2EE server deploy methods etc.
> By providing a interface on the Requirement/Capability we can leverage the workflows specific to the capability in a generic way. And the designer would be able to identify the contracted calls that are made available.
> https://www.oasis-open.org/apps/org/workgroup/tosca/document.php?document_id=49635
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