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https://issues.apache.org/jira/browse/ARIA-334?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16117291#comment-16117291
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Tal Liron commented on ARIA-334:
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The reason is to allow for future expansion of the base type without breaking
the base. There might be other things we'd like to set up for operation policy
in the future that is not just a map of arbitrary configuration strings.
> Policy for operation execution configuration
> --------------------------------------------
>
> Key: ARIA-334
> URL: https://issues.apache.org/jira/browse/ARIA-334
> Project: AriaTosca
> Issue Type: Story
> Reporter: Tal Liron
> Assignee: Tal Liron
>
> Our support for [using dependencies to configure operation
> execution|https://cwiki.apache.org/confluence/display/ARIATOSCA/Execution+Configuration]
> solves the technical problem, but it is very cumbersome to use in large
> templates.
> One solution is to use YAML macros (in the {{dsl_definitions}} section of the
> TOSCA template). But this is still awkward and ugly to have to insert the
> macro for every operation.
> The TOSCA way to do this is by policy. I suggest we support a new policy for
> operation execution, while *also* lettings user override those values locally
> per operation.
> Here's how it can be defined in the ARIA profile:
> {code}
> policy_types:
> aria.Operation:
> derived_from: tosca.policies.Root
> targets: [ tosca.nodes.Root, tosca.groups.Root ]
> properties:
> configuration:
> type: map
> entry_schema: string
> {code}
> You could then use it like so:
> {code}
> topology_template:
> policies:
> ssh:
> type: aria.Operation
> targets: [ bono, sprout, ralf, homer, homestead, vellum ]
> properties:
> configuration:
> ssh.user: { get_property: [ HOST, host, ssh.user ] }
> ssh.password: { get_property: [ HOST, host, ssh.password ] }
> ssh.address: { get_attribute: [ HOST, public_address ] }
> {code}
> What the above means is that for *all* operations on *all* interfaces of the
> target nodes (or groups) the above configuration parameters would be
> automatically applied (though local use of {{dependencies}} could override
> these values).
> The nice thing about this is that 1) it just needs to be defined once, and 2)
> it avoids our hacky {{dependencies}} notation.
> It might also make sense to add more properties to the policy for applying
> the policy only to specific interfaces or even specific operations and the
> target nodes. But that could possibly wait for a followup JIRA task.
> Note that the above example would also require us to fix intrinsic functions.
> As it stands, the parser would fail the above, because using the {{HOST}}
> keyword can only be used for properties inside a node or relationship. We
> would thus also need to allow for policies to use {{HOST}}, and assume it
> applies to the target node.
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