Rudder

The chosen format, as documented in http://www.rudder-project.org/doc-3.1/_using_properties.html, is the following:

${node.properties[datacenter]}

We must use the same in directive, at least for the data access.

Question: do we want to let the possiblity to have in a directive parameter

${node.properties[datacenter]}

${rudder.node.properties[datacenter]}

Personnaly, I don't think it is a good idea, because it's extremelly surprising (vastly different behaviour for almost the same thing). And a work around can certainly be used by calling the full CFEngine variable name (i.e:
${properties.property__var_rudder_cfengine_community_inputs_properties_d_properties_json[properties][datacenter]} - this one won't be changed at generation time).

I think replace a perfectly regular cfengine variable is also surprising for the user knowing cfengine and knowing how to use it.

A different argument would be that we want to be as much as possible independent of the underlying agent, so things from the user in the interface must be as much as possible processed before being sent to the agent.

For other comments on the directive part, please use: http://www.rudder-project.org/redmine/issues/9057