proxied runtime properties #134
Description
Runtime properties are a bad idea when they are copies of any information that might change over time. This invites consistency problems. I suggest an enhancement to the DSL that allows the definition of runtime properties that are functions rather than simple map values (or some other scheme with the equivalent effect). This could be accomplished either with a dict subclass or a new API. Plugin defined types could define valid runtime properties (as required by TOSCA anyway), and in that definition be able to associate a plugin function or functions (essentially getters and setters).
This feature would be useful both for underlying Cloud providers, and also for "deployment proxy" types of scenarios. For example, rather than copying outputs from a target deployment, the deployment proxy would actually "proxy" the values in lazy fashion from the target deployment.